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Saturday 29 October 2011

Seputar Bateray Notebook

Setelah sekian lama g pernah posting lg,,,,,

Perangkat notebook jaman sekarang kebanyakan menggunkan Baterai jenis Lithium (Li-On). Berikut ini adalah karakteristik dari baterai tersebut:

Jika package battere Li-Ion dibuka, sebetulnya didalamnya mengandung beberapa buah battere kecil yang disebut sebagai CELL. Semakin banyak CELL-nya (artinya semakin banyak battere-nya), akan membuat daya tahan-nya lebih lama. Saat ini jumlah CELL pada Baterai Notebook berkisar antara 4, 6 dan 8 Cell.
Jumlah CELL juga akan mempengaruhi berat battere-nya, dan berimbas pada berat notebook secara keseluruhan. Inilah yang menjelaskan kenapa notebook ringan juga menggunakan Baterai dengan jumlah cell sedikit. Misalnya : Notebook ORIS menggunakan Baterai 4-cell.
  • Baterai Li-Ion TIDAK mengenal “Memory Effect”, yaitu suatu kondisi dimana jika battere tidak di-charge sampai full (100%) maka kemampuannya akan berkurang. Jadi tidak ada istilah bahwa jumlah pemakaian charge akan mempengaruhi kondisi Baterai tsb.
  • Jika di-charge 100% dan disimpan pada suhu rata-rata 25? maka kemampuan / umur Baterai Li-Ion akan berkurang 20% setiap tahunnya. Ini dalam pemakaian normal.
  • Pada saat notebook tidak digunakan, maka charge Baterai sebaiknya rata-rata 40% saja (jangan sampai di-charge penuh). Karena jika keadaan full charge, kondisi itu akan membuat battere lebih banyak kehilangan daya tahannya. Ini juga menjelaskan kenapa jika kita membeli notebook / HP baru, battere selalu TIDAK DALAM KEADAAN PENUH.
  • Battere Li-Ion juga akan berkurang kemampuannya apabila suhu menjadi semakin panas. Ini yang menjelaskan kenapa pada notebook Celeron M, daya tahan Baterai semakin berkurang. Celeron M itu tidak memiliki fitur SpeedStep Technology seperti pada Pentium M / Core Duo, sehingga clock speed tidak bisa diturunkan dan membuat notebook semakin panas.
  • Teknologi kimia Li-Ion sebetulnya aman apabila digunakan secara wajar dan sesuai petunjuk. Tapi baterai ini juga dapat MELEDAK / TERBAKAR pada kondisi tertentu, seperti pada kondisi panas yang ekstrim dan berlebihan. Sebaiknya jangan meletakkan notebook pada mobil yang terparkir terbuka pada siang hari yg terik !
  • Berbeda dengan tipe Baterai lainnya seperti Ni-Cd, Li-Ion dapat di-charged berulang kali tanpa kehilangan kualitasnya. Pada saat Notebook tidak digunakan dalam waktu lama, sebaiknya charge Baterai jangan melebihi 40% agar pengurangan umur Baterai tidak terlalu cepat.
  • Life cycle baterai Lithium (Li-On) adalah sekitar 400-600 cycle charge dan recharge dimana setelah cycle tersebut maka akan terjadi penurunan kualitas Baterai. Karena lithium saat di charge dari kondisi 1% ke 100% itu dianggapnya sama saja dengan charge dari 99% ke 100%, yakni 1x life cycle. Saat life cyclenya semakin banyak, kapasitas baterai akan semakin berkurang jadi perhatikan metoda cycle recharge anda.


Pertanyaan umum dan problem yang sering terjadi pada baterai Notebook:


Saya baru pakai 3 bulan/1tahun kok baterai sudah tidak bisa dipakai :

    Baterai dipakai BUKAN BERDASARKAN WAKTU (hari, bulan, tahun), tetapi di-DIHITUNG berdasarkan CYCLE CHARGE-DISCHARGE, setiap satu cycle kemampuan berdasarkan kalkulasi BOARD BATTERY akan berkurang, bukan kemampuan cell baterai. Dimana BOARD BATTERY ada batasan minimum kemampuan baterai yang diperbolehkan. Pada umumnya baterai bisa sampai 400-600 cycle. Jadi kalau dalam satu hari melakukan 30 cycle, kurang lebih baterai dalam 10 hari akan drop

  1. Baterai saya charge kok tidak penuh2x hanya sampai xx% :
  2. Kenapa tidak penuh2x, karena Current Capacity di BOARD BATTERY tidak sinkron/SAMA dengan perhitungan Arus dan Voltage CELL BATTERY (CELL IMPEDANCE). Ada beberapa type yang bisa di kalibrasi ada yang di LOCK oleh MANUFACTURE BATTERY (Bukan Manufacture laptop).

  3. Lampu charge baterai menyala tetapi kalau adaptor di cabut laptop ikut mati / baterai tidak berfungsi normal :
  4. Kondisi ini biasanya karena SAFETY CIRCUIT di BOARD BATTERY sudah rusak, bisa di akibatkan over current (I), over voltage (V) maupun heat atau panas. Dan didalam BOARD BATTERY terdapat safety circuit 3 lapis dan CUKUP CERDAS

  5. Baterai saya simpan (tidak dipasang di laptop) setelah beberapa waktu kok tidak bisa dipakai lagi. Karena KATA ORANG kalau baterai mau awet lebih baik dicabut :
  6. Didalam BOARD BATTERY terdapat “self discharge/day” parameter dimana apabila battery tidak dipakai akan mengurangi “Current Capacity” di BOARD BATTERY , dimana ada minimum CURRENT CAPACITY yang di ijinkan oleh BOARD BATTERY. Apabila terlalu rendah maka BOARD BATTERY akan mengaktifkan SAFETY CIRCUIT, alias bunuh diri.


Tips dalam penggunaan Baterai notebook

  • Saat mengunakan baterai atau notebook baru discharge sampai kosong daya bawaan dari pabrik kemudia charge penuh dalam kondisi mati dalam waktu 4-8 jam agar cell baterai optimal.
  • Battere Li-Ion tidak boleh dikosongkan sampai 0% terlalu sering.
  • Gunakan baterai dengan optimal artinya manfaatkan life cycle dengan baik jangan ketika baterai masih 90% atau 80% langsung di charge.
  • Jangan di charge sampai 100% kemudia melepas baterai dari notebook, bila ingin meyimpan baterai dengan melepas dari notebook pastikan kondisi baterai dalam kapasitas 40-60%.
  • Metode melepas baterai ketika menggunakan listrik AC tidak serta merta membuat baterai menjadi awet dibalik itu ada resiko notebook mengalami kerusakan lain saat hanya mengunakan listrik AC dan terjadi pemadaman listrik.
  • Usahakan gunakan notebook dalam kondisi temperature ruangan yg baik jangan terlalu panas Karena panas merupakan musuh utama baterai Lithium (Li-On) ada baiknya menggunakan perangkat pendingin notebook seperti external cooling notebook.
  • Lakukan kalibrasi secara berkala terhadap baterai dengan cara melakukan satu kali discharge penuh (dari kapasitas 100% menjadi sekitar 3%) kemudian diikuti pengisian penuh baterai dengan mematikan notebook.
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Wednesday 24 August 2011

Cisco: How to configure NAT - Network Address Translation

This brief tutorial will let you configure NAT overload, or how to enable Internet access to multiple PCs of your LAN using only 1 public IP address. This type of NAT can easily be used at home when you have a Cisco 800 series xDSL router.


The first step is to define the addresses that will need to be NAT’d, this is done using a standard access-list:

access-list 1 permit your_lan_address_range
example: access-list 1 permit 192.168.1.0

Now that we defined the addresses that are allowed to use the NAT address we enable the actual NAT:
ip nat inside source list access-list number interface overload
example: ip nat inside source list 1 dialer0 overload

This command states that it will use the addresses from the access-list we defined in step 1 and NAT it to the Public IP address on the interface, e.g. serial 0, dialer 0, ethernet 1,… The overload keyword specifies that multiple LAN addresses can be NAT’d to that address. The router uses the TCP and UDP ports of the hosts [LAN addresses] to translate the public IP address back to the originating local host address.

The last steps we need to configure is to tell the router which our inside and outside addresses. This is achieved using the following commands:
- for the inside
conf t
interface ethernet | fastethernet number
ip nat inside

- for the outside, assume we are dealing with an xDSL router
conf t
interface dialer0
ip nat outside

Now that NAT is configured we can check to see which addresses are being used by using the show ip nat translations commands.

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Configuring DHCP to work with Cisco Manager

In this case from a Windows Server 2000 or 2003 system, with Cisco Call Manager (CCM). When introducing CCM into environments with an exsiting DHCP infrastructure, problems may occur because Cisco IP phones require additional information from the DHCP server when they startup.

Following the steps of DHCP server on the CCM hardware :

1) Start the DHCP server software that is already installed on your server (it comes with Server 2000 or Server 2003) buy clicking on “Start” then “Setting” then “Control Panel”. After the Control Panel open click on the “Administrative Tools” icon, and then the “DHCP” icon.

2) After the DHCP management console opens click on “Action” then select “New Scope…” then “OK” to the “New Scope Wizard”, then type in the name of your scope, this can be almost anything you would like, I named mine “voip_scope”, you can also give it a description if you like, I did not.

3) Then click “Next” and enter a start IP address and a end IP address, then use the up and down arrow buttons to increases or decrees the length of your sub-net mask, (just keep clicking the arrow buttons till you see the sub-net mask you what to use) and then click “Next”.

4) Next you will be asked to enter any address you do not want issue out be the DHCP server, maybe you are saving some static addresses for you router and/or servers. You can enter in just one address by entering the same address in the start and end boxes, or a range of addresses be putting the first or lowest in the start box, and the last or highest in the end box, then click “Next”.

5) You will be asked how long you want the lease to be good for; I leave it to the default and click “Next”.

6) Next you are asked if you want to set up the DHCP options now, these are the options the DHCP server will pass along to the requesting client with it’s new IP address, I select “Yes” and enter the “Router (Default Gateway) IP address, and click “Add” and then click “Next”.

7) Next you can enter and any Domain information you have and then click “Add” then “Next”.

8) You can now add and WINS information you have, I leave mind blank, and click “Next”. The lest question you are asked is if you want to active the scope now, I select “Yes” and click “Next” and then “Finish” to close the “New Scope Wizard”.

9) In the right hand plane of the DHCP management console windows double click on “Scope Options”, the click “Action” and select “Configure Options…” then in the “Scope Options” box click “066 Boot Server Host Name” to check that option, and in the “String value” box enter the IP address of your TFTP server, mine happens to be the same as my CCM, and click OK. Now when a client asked for a new IP address it will also get the TFTP server’s address, which the Cisco IP phones need to boot.


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Tuesday 23 August 2011

Learning Cisco CCNA with Simulators

Passing the CCNA is all about knowing the details of how things work, and knowing CSMA/CD theory and how to define collision domains is of the lots of details you have got to master. In the next part of this CCNA tutorial, we'll take a glance at broadcast domains, and how defining broadcast domains in the right places can dramatically cut down on unnecessary traffic on your network.

As you study for your CCNA and CCNP exams, if you are getting hands-on practice in your home lab or rack rental service, you are going to be sending lots of pings. As a CCNA or CCNP candidate, you know that exclamation points (!!) as a ping return indicates that you have IP connectivity to the remote location. periods (\.\...) indicates that you do not have that connectivity.

Students and Professionals that got their CCNA certification will normally finish up in one of categories. The 1st: guys and gals entering the IT world. The 2nd section: individuals who need to make the transition from Local Area Network to Wide Area Network. WAN engineers and administrators make the 3rd section. In the event that they got their CCNA certification, it is because they yearn to move up the ladder.
Keep learning & improving after your've earned your certification. It is simple to quickly forget what you don't use. Feel free to take off a couple days to reward yourself for all that hard work. Then, of work, it is time to strap back in & study. Keep reviewing your CCNA topics, & start on your first CCNP examination. Lots of folks who get that glorious CCNA certificate will basically forget the knowledge they obtained because they gave up studying one time the examination was over.
I give strong recommendation to video tutorials, Exams Testing Engines, Study Guides, Preparation Labs, Q & A for CCNA certification package. Indeed it is a actual worth to money. Here you can get configuration of cisco devices along with proper explanation but the disadvantage is it does not cover everything in examination so you need to go for CCNA CCNA exams training simulators.
Get practice check program

Cisco Simulators
There's free or paid cisco CCNA exams training simulators available on web. It is necessary to get your hands on these simulators so you get on hand experience in configuration cisco devices. In case you have budge you can also build your Cisco home lab.

Today plenty of companies sell practice exams that help to attempt CCNA CCNA examination training. You require to buy them & go for your first check. In the first attempt you may fail but don't get discouraged. Plenty of practice check program are the bank of questions, each divided in to four practice tests. You are necessary to attempt the practice tests four times. Finally you take final practice examination including the all the questions. At this point of time you are prepared to go for actual examination.

If your preparing for career alter & looking for CCNA Training the best online training provider that provide the all the & complete MCTS certification exams training in package, certkingdom self study training kits, save your money on bootcamps, training institutes, It is also save your travelling & time. All training materials are "Guaranteed" to pass your exams & get you certified on the fist attempt, due to best training they become no1 site 2009 & 2010.
In addition I recommend Certkindom.com is best and No1 site of 2008 which provide the complete Windows Server 2003 certified professionals training, Microsoft MCITP, Microsoft MCTS, Cisco CCNA, Cisco CCIE, CompTIA A+, IBM, Citrix, PMP, ISC, and lots more online training self study kits, saving your time and money on all those expensive bootcamps, conventional training institutes where you have take admission pay fees first and if you don't want to continue no refunds no transfer to any other training course, If you planed to take CCNA or specialization in MCSE 2003 all the process starts again; as for getting online training can be much beneficial and you don't need to take for fill any from to switch your training on any desire certification.
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4 Tips to Use a CCNA Study Guide

Try to look for more CCNA study guides & CCNA books. This may help you understand things in over fashion. Reading a range of CCNA study guides about the same idea makes you understand it more & perhaps simple. Go to Amazon & buy CCNA study guides from different study authors as you can.

A CCNA study guide is tremendous gizmo to pass the CCNA Certification examination if used correctly. Regrettably, some CCNA students use CCNA study guides badly, & this leads to confusions related to the CCNA topics & decrease the CCNA candidate's chances to pass the CCNA check. In the upcoming paragraphs, you'll some tips on how to make use of CCNA study guides.

of the ways to benefit from you CCNA study guide is to make use of it as a checklist. all of CCNA study guide provide knowledge that you are supposed to know to pass the CCNA certification examination. In the coursework of your CCNA study journey, try to mark a check to each element in your CCNA study guide when you have comprehended it & configured its related commands. When you finish studying, review you CCNA study guide to see in case you have left or more items unchecked. If yes, use other CCNA books & other networking books on the item or items you still don't understand. You may also do a research on Google & find lots of useful knowledge, document, & even some free CCNA study guides.

Finally, try to build your own CCNA study guide by assembling all the notes you have made as you were studying. In addition, try to share your CCNA study guide with other people studying for the CCNA examination.

Do not make the error of relying on CCNA study guide alone. As historicallyin the past mentioned, CCNA study guides are in no way complete, & you must not treat it as the single source of knowledge to help you pass your CCNA examination. In case you are enrolled in a CCNA boot camp, pay attention in the coursework of your CCNA study activities in the boot camp to help you benefit the most out of your CCNA study guide.

Read more: http://www.articlesbase.com/computers-articles/4-tips-to-use-a-ccna-study-guide-perfectly-4305027.html#ixzz1VsdoxfZE
Under Creative Commons License: Attribution No Derivatives
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Classful IP Subnet Calculations

1. IP Addressing

At this point you should know that IP, the Internet Protocol, is a network layer (OSI layer 3) protocol, used to route packets between hosts on different networks. To suit this purpose, IP must define an addressing scheme, so that a packet's intended destination can be indicated.

An IP address is composed of 32 bits. These 32 bits are divided into 4 octets of 8 bits each. You may have seen an IP address represented like this: 172.68.15.24. We must remember, however, that the computer understands this number only in binary, so we must often deal with them in binary. Many people are intimidated by this initially, but soon find that it is not difficult. If you do not allow yourself to be flustered, you can master this topic.

IP addresses are assigned to orginazations in blocks. Each block belongs to one of three classes: class A, class B, or class C. You can tell what class an IP address is by the value in its first octet.

Class A 1-126
Class B 128-191
Class C 192 -->

An IP address consists of two fields. The first field identifies the network, and the second field identifies the node on the network. Which bits of the address are in the network field and which bits are in the host field is determined by the subnet mask.

When a class A IP license is granted, you are assigned something like this: 99.0.0.0. Only the value of the bits in the first octet are assigned. This means you are free to assign any values you wish in the second, third and fourth octets.

The defualt subnet mask for a class A network is 255.0.0.0. High bits, ones, indicate the bits that are part of the network field of the IP address. The default subnet mask does not create subnets. Therefor, a class A network with the default subnet mask is one network. The three octets that are unassigned and unmasked are part of the host field of the address. There is a total of 24 bits in those three octets. Each bit can be in one of two states. Therefor, 2^24 is the number of host addresses that can be assigned on that network, almost. Two addresses are reserved on every network, x.x.x.0 and x.x.x.255. So the total number of hosts possible on this network is 2^24. 2^24-2=16,777,214 hosts for a class A IP network.

When a class B license is granted, the first two octets are assigned. For example, 172.198.x.x. The default subnet mask for a class B is 255.255.0.0. One network, two octets free, 16 bits for the host address field. 2^16-2=65,534 possible host addresses on a class B IP network.

When a class C license is granted, the first three octets are assigned, for example: 193.52.16.0. The default subnet mask for a class C is 255.255.255.0. Once octet makes up the host address field. 2^8-2=254 host addresses possible on a class C network.

2. Reason for Subnetting

We said that the default subnet mask for a class A IP network is 255.0.0.0. Once octet only of a class A network address identifies the network, with this subnet mask. This leaves three octets of 8 bits each, or 24 bits, to identify the host on that one network. 2^24=16,777,216 addresses. Two addresses are reserved, x.x.x.0 and x.x.x.255. 16,777,214 nodes can be assigned an IP address on this network.

It is highly unlikely that any organization would want one network of 16,777,214 nodes. They might want that many devices connected in a wide area network (WAN), thus capablee of communicating when neccessary, but they will want to subdivide this huge network into mostly self-contained subnetworks of nodes that communicate with each other often. This is called subnetting.

To understand why, consider what would happen in either a broadcast or a token passing network that consisted of over 16,000,000 nodes. Nothing would happen. It simply would not work. Though the problem is not as drastic, class B and class C IP networks are often subnetted, also.

The subnet mask is used to subdivide an IP network into subnets. This is a division that takes place in OSI layer 3, so it is a logical division that is created by the addressing scheme. This logical division is usually combined with a physical division. Many subnets are physically isolated from the rest of the network by a device such as a router or a switch. This aspect of subnetting is discussed in Unit 3--Data Link Layer.

3. How Subnetting Works

The bits of an address that are masked by the subnet mask are the bits that make up the network field of the address. To subnet, the default subnet mask for a network is extended to cover bits of the address that would otherwise be part of the host field. Once these bits are masked, they become part of the network field, and are used to identify subnets of the larger network.

Here is where we begin dealing with both addresses and subnetmasks in binary. Get yourself a cold beverage, stretch, take a deep breath and don't worry. Once you get your brain around the concepts, it is not difficult. You just have to keep trying until the light goes on.

3.1 Translating Binary to Decimal

Both IP addresses and subnet masks are composed of 32 bits divided into 4 octets of 8 bits each. Here is how a single octet translates from binary to decimal. Consider an octet of all ones: 11111111.

128 64 32 16 8 4 2 1 ---  --  --  --  -  -  -  - 1  1  1  1  1  1  1  1  128 + 64 + 32 + 16 + 8 + 4 + 2 + 1 = 255 

Here's another: 10111001

128 64 32 16 8 4 2 1 ---  --  --  --  -  -  -  - 1  0  1  1  1  0  0  1 128 +  0 + 32  +16 + 8 + 0 + 0 + 1 = 185 

and 00000000

128 64   32   16   8   4   2   1 ---   --   --   --   -   -   -   -  0     0    0    0   0   0   0   0  0  +  0 +  0 +  0 + 0 + 0 + 0 + 0 = 0 

3.2 Converting Decimal to Binary

Converting decimal to binary is similar. Consider 175:

128 64  32   16   8   4   2   1 ---   --   --   --   -   -   -   -  1     0    1    0   1   1   1   1 128 +  0 + 32 +  0 + 8 + 4 + 2 + 1 = 175 

175=10101111

3.3 Simple Subnetting

The simpliest way to subnet is to take the octet in the subnet mask that covers the first unassigned octet in the IP address block, and make all its bits high. Remember, a high bit, a 1, in the subnet mask indicates that that corresponding bit in the IP address is part of the network field. So, if you have a class B network 172.160.0.0, with the subnet mask 255.255.0.0, you have one network with 65, 534 possible addresses. If you take that subnet mask and make all the bits in the third octet high

128 64   32   16   8   4   2   1 ---   --   --   --   -   -   -   -  1     1    1    1   1   1   1   1 128 + 64 + 32 + 16 + 8 + 4 + 2 + 1 = 255 

you get the subnet mask 255.255.255.0.

172.60.  0. 0 255.255.255.0 

Now the third octet of all the addresses on this network are part of the network field instead of the host field. That is one octet, or eight bits, that can be manipulated to create subnets. 2^8=256 possible subnets now on this class B network.

One octet is left for the host field. 2^8-2=254 possible host addressed on each subnet.

3.4 Advanced Subnetting

That is the simplist way to subnet, but it may not be the most desirable. You might not want 256 subnets on your class B network. Instead, you might use a subnet mask like 255.255.224.0. How many subnets would this give you? The first step is to see how many bits are allocated to the network by this mask.

128 64   32   16   8   4   2   1 ---   --   --   --   -   -   -   -  1     1    1    0   0   0   0   0 128 + 64 + 32 +  0 + 0 + 0 + 0 + 0 = 224 

3 bits are allocated. 2^3=8 subnets.

How many hosts on each subnet? Well, 5 bits from this octet are left for the host field, and 8 bits in the fourth octet, for a total of 13 bits in the host field. 2^13-2=8190 possible hosts on each subnet.

The subnet mask is always extended by masking off the next bit in the address, from left to right. Thus, the last octet in the subnet mask will always be one of these: 128, 192, 224, 240, 248, 252, 254 or 255.

Given the IP address of a host and the subnet address for the network, you need to be able to calculate which subnet that host is on. To do this we compare the binary representation of the pertinent octet of the subnet mask witht he binary representation of the corresponding octet in the IP address. Example:

IP address=172.60.50.2 subnet mask=255.255.224.0  50= 00110010 224=11100000 

We perform a logical AND on these two numbers. We will be left with only the bits where there is a one in both octets.

00110010 11100000 -------- 00100000=32 

This host is on subnet 172.60.32.0.

We also need to be able to find the range of assignable IP addresses on this subnet. To do this, we take the binary that tells us the subnet address, in this case 00100000, and compare it with the subnet mask.

00100000 11100000 

The bits convered by the mask we will leave as they are. The rest of the bits we make high. So

00100000 11100000 -------- 0011111=63 

The range of assignable IP addresses on the subnet 172.60.32.0 is 172.60.32.1-172.60.63.254.

On every network and subnet, two addresses are reserved. At the low end of the range of addresses for the network or subnet, in this case 172.60.32.0, is the address for the network or subnet itself. The address at the high end of the range of addresses, in this case 172.60.63.255, is the broadcast address. Any message sent to the broadcast address will be received by every host on the network.

4. Sample Problem

Here is a sample problem for you to calculate. When you are done, you can check your answers using an online subnet calcualtor at SubnetOnline.com.

IP address:  154.16.52.16 subnet mask:  255.255.240.0  Find: Number of subnets possible on this network: Number of hosts possible on each subnet: Which subnet this address is on: Range of addresses on that subnet: 
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Monday 22 August 2011

Configure your Cisco Router


If you have just turned on the router, it will be completely unconfigured. If it is already configured, you may want to view its current configuration. Even if it has not been previously configured, you should familiarize yourself with the show commands before beginning to configure the router. Enter privileged mode by issuing the command enable, then issue several show commands to see what they display. Remember, the command show ? will display all the showcommands aavailable in the current mode. Definately try out the following commands:

When you enter privileged mode by using the command enable, you are in the top-level mode of privileged mode, also known in this document as "parent mode." It is in this top-level or parent mode that you can display most of the information about the router. As you now know, you do this with the show commands. Here you can learn the configuration of interfaces and whether they are up or down. You can display what IP protocols are in use, such as dynamic routing protocols. You can view the route and ARP tables, and these are just a few of the more important options.

As you configure the router, you will enter various sub-modes to set options, then return to the parent mode to display the results of your commands. You also return to the parent mode to enter other sub-modes. To return to the parent mode, you hit ctrl-z. This puts any commands you have just issued into affect, and returns you to parent mode.

- a.

Global configuration (config)


To configure any feature of the router, you must enter configuration mode. This is the first sub-mode of the parent mode. In the parent mode, you issue the command config.
Router#config
Router(config)#

As demonstrated above, the prompt changes to indicate the mode that you are now in.

In connfiguration mode you can set options that apply system-wide, also refered to as "global configurations." For instance, it is a good idea to name your router so that you can easily identify it. You do this in configuration mode with the hostname command.

Router(config)#hostname ExampleName

ExampleName(config)#

As demonstrated above, when you set the name of the host with the hostname command, the prompt immediately changes by replacing Router with ExampleName. (Note: It is a good idea to name your routers with an organized naming scheme.)

Another useful command issued from config mode is the command to designate the DNS server to be used by the router:

ExampleName(config)#ip name-server aa.bb.cc.dd

ExampleName(config)#ctrl-Z
ExampleName#

This is also where you set the password for privileged mode.

ExampleName(config)#enable secret examplepassword

ExampleName(config)#ctrl-Z
ExampleName#

Until you hit ctrl-Z (or type exit until you reach parent mode) your command has not been put into affect. You can enter config mode, issue several different commands, then hit ctrl-Z to activate them all. Each time you hit ctrl-Z you return to parent mode and the prompt:

ExampleName#

Here you use show commands to verify the results of the commands you issued in config mode. To verify the results of the ip name-server command, issue the command show host.

Configuring Cisco router interfaces

Cisco interface naming is straightforward. Individual interfaces are referred to by this convention:

media type slot#/port#

"Media type" refers to the type of media that the port is an interface for, such as Ethernet, Token Ring, FDDI, serial, etc. Slot numbers are only applicable for routers that provide slots into which you can install modules. These modules contain several ports for a given media. The 7200 series is an example. These modules are even hot-swapable. You can remove a module from a slot and replace it with a different module, without interrupting service provided by the other modules installed in the router. These slots are numbered on the router.

Port number refers to the port in reference to the other ports in that module. Numbering is left-to-right, and all numbering starts at 0, not at one.

For example, a Cisco 7206 is a 7200 series router with six slots. To refer to an interface that is the third port of an Ethernet module installed in the sixth slot, it would be interface ethernet 6/2. Therefor, to display the configuration of that interface you use the command:

ExampleName#show interface ethernet 6/2

If your router does not have slots, like a 1600, then the interface name consists only of:

media type port#

For example:

ExampleName#show interface serial 0

Here is an example of configuring a serial port with an IP address:

ExampleName#config

ExampleName(config)#interface serial 1/1
ExampleName(config-if)#ip address 192.168.155.2 255.255.255.0
ExampleName(config-if)#ipv6 address fe80::230:1bff:fe80:b8ea/64
ExampleName(config-if)#ipv6 enable
ExampleName(config-if)#no shutdown
ExampleName(config-if)#ctrl-Z
ExampleName#

Then to verify configuration:

ExampleName#show interface serial 1/1

Note the no shutdown command. An interface may be correctly configured and physically connected, yet be "administratively down." In this state it will not function. The command for causing an interface to be administratively down is shutdown.

ExampleName(config)#interface serial 1/1

ExampleName(config-if)#shutdown
ExampleName(config-if)#ctrl-Z
ExampleName#show interface serial 1/1

In the Cisco IOS, the way to reverse or delete the results of any command is to simply put no infront of it. For instance, if we wanted to unassign the IP address we had assigned to interface serial 1/1:

ExampleName(config)#interface serail 1/1

ExampleName(config-if)#no ip address 192.168.155.2 255.255.255.0
ExampleName(config-if)ctrl-Z
ExampleName#show interface serial 1/1

Configuring most interfaces for LAN connections might consist only of assigning a network layer address and making sure the interface is not administratively shutdown. It is usually not necessary to stipulate data-link layer encapsulation. Note that it is often necessary to stipulate the appropriate data-link layer encapsulation for WAN connections, such as frame-relay and ATM. Serial interfaces default to using HDLC. A discussion of data-link protocols is outside the scope of this document. You will need to look up the IOS command encapsulation for more details.

Configuring Cisco Routing

IP routing is automatically enabled on Cisco routers. If it has been previously disabled on your router, you turn it back on in config mode with the command ip routing.

ExampleName(config)#ip routing

ExampleName(config)#ctrl-Z

To enable IPv6 routing, use the command ipv6 unicast-routing.

ExampleName(config)#ipv6 unicast-routing

ExampleName(config)#ctrl-Z

There are two main ways a router knows where to send packets. The administrator can assign static routes, or the router can learn routes by employing a dynamic routing protocol.

Static routes are generally used in very simple networks or in particular cases that necessitate their use. To create a static route, the administrator tells the router operating system that any network traffic destined for a specified network layer address should be forwarded to a similiarly specified network layer address. In the Cisco IOS this is done with the ip route and ipv6 route commands.

ExampleName#config

ExampleName(config)#ip route 172.16.0.0 255.255.255.0 192.168.150.1
ExampleName(config)#ctrl-Z
ExampleName#show ip route
ExampleName#config
ExampleName(config)#ipv6 route fe80::230:1bff:fe80::/64 fe80::230:1bff:fe80::1
ExampleName(config)#ctrl-Z
ExampleName#show ipv6 route

Two things to be said about this example. First, the packet destination address must include the subnet mask for that destination network. Second, the address it is to be forwarded to is the specified addres of the next router along the path to the destination. This is the most common way of setting up a static route, and the only one this document covers. Be aware, however, that there are other methods.

Dynamic routing protocols, running on connected routers, enable those routers to share routing information. This enables routers to learn the routes available to them. The advantage of this method is that routers are able to adjust to changes in network topologies. If a route is physically removed, or a neighbor router goes down, the routing protocol searches for a new route. Routing protocols can even dynamically choose between possible routes based on variables such as network congestion or network reliability.

There are many different routing protocols, and they all use different variables, known as "metrics," to decide upon appropriate routes. Unfortunately, a router needs to be running the same routing protocols as its neighbors. Many routers can, however, run mutliple protocols. Also, many protocols are designed to be able to pass routing information to other routing protocols. This is called "redistribution."

Routing protocols are a complex topic and this document contains only this superficial description of them. There is much to learn about them, and there are many sources of information about them available. An excelent source of information on this topic is Cisco's website, http://www.cisco.com.

IPv6 configuration with IOS

This is a seperate section because IPv6 is new to most people, and they will be looking specifically for information about configuring IPv6. Examples of configuring IPv6 are included throughout the document, however, alongside IPv4. That is a more accurate reflection of how you will work with IPv6 on a day-to-day basis. Once the newness of IPv6 passes, it will be one more piece in the familiar puzzle.

The important concept to understand when configuring IPv6 is that IPv4 and IPv6 exist in parrallel. One is not a replacement for the other, at least not in the way it is treated by the operating system. A term for this is dual stack. An interface can have an IPv4 address and no IPv6 address. Or an IPv6 address and no IPv4 address. Or both an IPv4 address and an IPv6 address. Examples:

IPv4 only

!

interface FastEthernet0/0
ip address 192.168.1.138 255.255.255.0
!

IPv6 only

!

interface FastEthernet0/0
ipv6 address fe80::230:1bff:fe80::/64
ipv6 enable
!

IPv4 and IPv6

!

interface FastEthernet0/0
ip address 192.168.1.138 255.255.255.0
ipv6 address fe80::230:1bff:fe80::/64
ipv6 enable
!

Notice that there are seperate but similiar commands for IPv4 and IPv6. To assign an IPv4 address,

ExampleName(config-if)#ip address 192.168.1.138 255.255.255.0

To assign an IPv6 address,

ExampleName(config-if)#ipv6 address fe80::230:1bff:fe80::/64

There are some bigger differences between IPv4 and IPv6 IOS commands. For example, the IPv6 equivilant of show ip arp, is show ipv6 neighbors.

3.5 Saving your Cisco Router configuration

Once you have configured routing on the router, and you have configured individual interfaces, your router should be capable of routing traffic. Give it a few moments to talk to its neighbors, then issue the commands show ip route and show ip arp. There should now be entries in these tables learned from the routing protocol.

If you turned the router off right now, and turned it on again, you would have to start configuration over again. Your running configuration is not saved to any perminent storage media. You can see this configuration with the command show running-config.

ExampleName#show running-config

You do want to save your successful running configuration. Issue the command copy running-config startup-config.

ExampleName#copy running-config startup-config

Your configuration is now saved to non-volatile RAM (NVRAM). Issue the command show startup-config.

ExampleName#show startup-config

Now any time you need to return your router to that configuration, issue the command copy startup-config running-config.

ExampleName#copy startup-config running-config


Example Cisco Router configuration

  1. Router>enable
  2. Router#config
  3. Router(config)#hostname N115-7206
  4. N115-7206(config)#interface serial 1/1
  5. N115-7206(config-if)ip address 192.168.155.2 255.255.255.0
  6. N115-7206(config-if)ipv6 address fe80::230:1bff:fe80:b8ea/64
  7. N115-7206(config-if)ipv6 enable
  8. N115-7206(config-if)no shutdown
  9. N115-7206(config-if)ctrl-z
  10. N115-7206#show interface serial 1/1
  11. N115-7206#config
  12. N115-7206(config)#interface ethernet 2/3
  13. N115-7206(config-if)#ip address 192.168.150.90 255.255.255.0
  14. N115-7206(config-if)#no shutdown
  15. N115-7206(config-if)#ctrl-z
  16. N115-7206#show interface ethernet 2/3
  17. N115-7206#config
  18. N115-7206(config)#ip name-server 172.16.0.10
  19. N115-7206(config)#ctrl-z
  20. N115-7206#ping archie.au
  21. N115-7206#config
  22. N115-7206(config)#enable secret password
  23. N115-7206(config)#ctrl-z
  24. N115-7206#copy running-config startup-config
  25. N115-7206#exit
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Started with Cisco


Initially you will probably configure your router from a terminal. If the router is already configured and at least one port is configured with an IP address, and it has a physical connection to the network, you might be able to telnet to the router and configure it across the network. If it is not already configured, then you will have to directly connect to it with a terminal and a serial cable. With any Windows box you can use Hyperterminal to easily connect to the router. Plug a serial cable into a serial (COM) port on the PC and the other end into the console port on the Cisco router. Start Hyperterminal, tell it which COM port to use and click OK. Set the speed of the connection to 9600 baud and click OK. If the router is not on, turn it on.

If you wish to configure the router from a Linux box, either Seyon or Minicom should work. At least one of them, and maybe both, will come with your Linux distribution.

Often you will need to hit the Enter key to see the prompt from the router. If it is unconfigured it will look like this:

Router>

If it has been previously configured with a hostname, it will look like this:

hostname of router>

If you have just turned on the router, after it boots it will ask you if you wish to begin initial configuration. Say no. If you say yes, it will put you in the menu interface. Say no.

- The Cisco IOS command-line interface is organized around the idea of modes. You move in and out of several different modes while configuring a router, and which mode you are in determines what commands you can use. Each mode has a set of commands available in that mode, and some of these commands are only available in that mode। In any mode, typing a question mark will display a list of the commands available in that mode.

When you first connect to the router and provide the password (if necessary), you enter EXEC mode, the first mode in which you can issue commands from the command-line. From here you can use such unprivileged commands as ping, telnet, and rlogin. You can also use some of the show commands to obtain information about the system. In unprivileged mode you use commands like, show version to display the version of the IOS the router is running. Typing show ? will diplay all the show commands available in the mode you are presently in.

Router>show ?

You must enter privileged mode to configure the router. You do this by using the command enable. Privileged mode will usually be password protected unless the router is unconfigured. You have the option of not password protecting privileged mode, but it is HIGHLY recommended that you do. When you issue the command enable and provide the password, you will enter privileged mode.

To help the user keep track of what mode they are in, the command-line prompt changes each time you enter a different mode. When you switch from unprivileged mode to privileged mode, the prompt changes from:

Router>

to

Router#

This would probably not be a big deal if there were just two modes. There are, in fact, numerous modes, and this feature is probably indispensable. Pay close attention to the prompt at all times.

Within privileged mode there are many sub-modes. In this document I do not closely follow Cisco terminology for this hierarchy of modes. I think that my explanation is clearer, frankly. Cisco describes two modes, unprivileged and privileged, and then a hierarchy of commands used in privileged mode. I reason that it is much clearer to understand if you just consider there to be many sub-modes of privileged mode, which I will also call parent mode. Once you enter privileged mode (parent mode) the prompt ends with a pound sign (#). There are numerous modes you can enter only after entering privileged mode. Each of these modes has a prompt of the form:

Router(arguments)#

They still all end with the pound sign. They are subsumed within privileged mode. Many of these modes have sub-modes of their own. Once you enter priliged mode, you have access to all the configuration information and options the IOS provides, either directly from the parent mode, or from one of its submodes.

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Read more ...

Monday 25 July 2011

computer game

A personal computer game (also known as a computer game or PC game) is a video game played on a personal computer, rather than on a video game console or arcade machine. Computer games have evolved from the simple graphics and gameplay of early titles like Spacewar!, to a wide range of more visually advanced titles.[1]

PC games are created by one or more game developers, often in conjunction with other specialists (such as game artists) and either published independently or through a third party publisher. They may then be distributed on physical media such as DVDs and CDs, as Internet-downloadable, possibly freely redistributable, software, or through online delivery services such as Direct2Drive and Steam. PC games often require specialized hardware in the user's computer in order to play, such as a specific generation of graphics processing unit or an Internet connection for online play, although these system requirements vary from game to game.

-

History

Although personal computers only became popular with the development of the microprocessor and microcomputer, computer gaming on mainframes and minicomputers had previously already existed. OXO, an adaptation of tic-tac-toe for the EDSAC, debuted in 1952. Another pioneer computer game was developed in 1961, when MIT students Martin Graetz and Alan Kotok, with MIT student Steve Russell, developed Spacewar! on a PDP-1 mainframe computer used for statistical calculations.[2]

The first generation of computer games were often text adventures or interactive fiction, in which the player communicated with the computer by entering commands through a keyboard. An early text-adventure, Adventure, was developed for the PDP-11 minicomputer by Will Crowther in 1976, and expanded by Don Woods in 1977.[3] By the 1980s, personal computers had become powerful enough to run games like Adventure, but by this time, graphics were beginning to become an important factor in games. Later games combined textual commands with basic graphics, as seen in the SSI Gold Box games such as Pool of Radiance, or Bard's Tale for example.

By the late 1970s to early 1980s, games were developed and distributed through hobbyist groups and gaming magazines, such as Creative Computing and later Computer Gaming World. These publications provided game code that could be typed into a computer and played, encouraging readers to submit their own software to competitions.[4] Microchess was one of the first games for microcomputers which was sold to the public. First sold in 1977, Microchess eventually sold over 50,000 copies on cassette tape.

Like with second-generation video game consoles at the time, early home computer games began gaining commercial success by capitalizing on the success of arcade games at the time with ports or clones of popular arcade games.[5][6] By 1982, the top-selling games for the Atari 400 were ports of Frogger and Centipede, while the top-selling game for the Texas Instruments TI-99/4A was the Space Invaders clone TI Invaders.[5] That same year, Pac-Man was ported to the Atari 800,[6] while Donkey Kong was licensed for the Coleco Adam.[7] In late 1981, Atari attempted to take legal action against unauthorized clones, particularly Pac-Man clones, despite some of these predating Atari's exclusive rights to the home versions of Namco's game.[6]

[edit] Industry crash

As the video game market became flooded with poor-quality cartridge games created by numerous companies attempting to enter the market, and over-production of high profile releases such as the Atari 2600 adaptations of Pac-Man and E.T. grossly underperformed, the popularity of personal computers for education rose dramatically. In 1983, consumer interest in console video games dwindled to historical lows, as interest in computer games rose.[8] The effects of the crash were largely limited to the console market, as established companies such as Atari posted record losses over subsequent years. Conversely, the home computer market boomed, as sales of low-cost color computers such as the Commodore 64 rose to record highs and developers such as Electronic Arts benefited from increasing interest in the platform.[8]

The console market experienced a resurgence in the United States with the release of the Nintendo Entertainment System (NES). In Europe, computer gaming continued to boom for many years after.[8] Computers such as the ZX Spectrum and BBC Micro were successful in the European market, where the NES was not as successful despite its monopoly in Japan and North America. The only 8-bit console to have any success in Europe would be the Sega Master System.[9] Meanwhile in Japan, both consoles and computers became major industries, with the console market dominated by Nintendo and the computer market dominated by NEC's PC-88 (1981) and PC-98 (1982). A key difference between Western and Japanese computers at the time was the display resolution, with Japanese systems using a higher resolution of 640x400 to accommodate Japanese text which in turn had an impact on game design and allowed more detailed graphics.[10]

[edit] New genres

Increasing adoption of the computer mouse, driven partially by the success of games such as the highly successful King's Quest series, and high resolution bitmap displays allowed the industry to include increasingly high-quality graphical interfaces in new releases. Meanwhile, the Commodore Amiga computer achieved great success in the market from its release in 1985, contributing to the rapid adoption of these new interface technologies.[11]

Further improvements to game artwork were made possible with the introduction of FM synthesis sound. Yamaha began manufacturing FM synth boards for computers in the early-mid 1980s, and by 1985, the FM-7 AV computer had built-in FM sound.[10] The first sound cards, such as AdLib's Music Synthesizer Card, soon appeared in 1987. These cards allowed IBM PC compatible computers to produce complex sounds using FM synthesis, where they had previously been limited to simple tones and beeps. However, the rise of the Creative Labs Sound Blaster card, released in 1989, which featured much higher sound quality due to the inclusion of a PCM channel and digital signal processor, led AdLib to file for bankruptcy by 1992. Also in 1989, the FM Towns computer included built-in PCM sound, in addition to a CD-ROM drive and 24-bit color graphics.[10]

In 1991, id Software produced an early first-person shooter, Hovertank 3D, which was the company's first in their line of highly influential games in the genre. There were also several other companies that produced early first-person shooters, such as Arsys Software's Star Cruiser,[12] which featured fully 3D polygonal graphics in 1988,[13] and Accolade's Day of the Viper in 1989. Id Software went on to develop Wolfenstein 3D in 1992, which helped to popularize the genre, kick-starting a genre that would become one of the highest-selling in modern times.[14] The game was originally distributed through the shareware distribution model, allowing players to try a limited part of the game for free but requiring payment to play the rest, and represented one of the first uses of texture mapping graphics in a popular game, along with Ultima Underworld.[15]

While leading Sega and Nintendo console systems kept their CPU speed at 3-7 MHz, the 486 PC processor ran much faster, allowing it to perform many more calculations per second. The 1993 release of Doom on the PC was a breakthrough in 3D graphics, and was soon ported to various game consoles in a general shift toward greater realism.[16] In the same time frame, games such as Myst took advantage of the new CD-ROM delivery format to include many more assets (sound, images, video) for a richer game experience.

Many early PC games included extras such as the peril-sensitive sunglasses that shipped with The Hitchhiker's Guide to the Galaxy. These extras gradually became less common, but many games were still sold in the traditional over-sized boxes that used to hold the extra "feelies". Today, such extras are usually found only in Special Edition versions of games, such as Battlechests from Blizzard.[17]

[edit] Contemporary gaming

By 1996, the rise of Microsoft Windows and success of 3D console titles such as Super Mario 64 sparked great interest in hardware accelerated 3D graphics on the IBM PC compatible, and soon resulted in attempts to produce affordable solutions with the ATI Rage, Matrox Mystique and S3 ViRGE. Tomb Raider, which was released in 1996, was one of the first third person shooter games and was praised for its revolutionary graphics. As 3D graphics libraries such as DirectX and OpenGL matured and knocked proprietary interfaces out of the market, these platforms gained greater acceptance in the market, particularly with their demonstrated benefits in games such as Unreal.[18] However, major changes to the Microsoft Windows operating system, by then the market leader, made many older MS-DOS-based games unplayable on Windows NT, and later, Windows XP (without using an emulator, such as DOSbox).[19][20]

The faster graphics accelerators and improving CPU technology resulted in increasing levels of realism in computer games. During this time, the improvements introduced with products such as ATI's Radeon R300 and NVidia's GeForce 6 Series have allowed developers to increase the complexity of modern game engines. PC gaming currently tends strongly toward improvements in 3D graphics.[21]

Unlike the generally accepted push for improved graphical performance, the use of physics engines in computer games has become a matter of debate since announcement and 2005 release of the nVidia PhysX PPU, ostensibly competing with middleware such as the Havok physics engine. Issues such as difficulty in ensuring consistent experiences for all players,[22] and the uncertain benefit of first generation PhysX cards in games such as Tom Clancy's Ghost Recon Advanced Warfighter and City of Villains, prompted arguments over the value of such technology.[23][24]

Similarly, many game publishers began to experiment with new forms of marketing. Chief among these alternative strategies is episodic gaming, an adaptation of the older concept of expansion packs, in which game content is provided in smaller quantities but for a proportionally lower price. Titles such as Half-Life 2: Episode One took advantage of the idea, with mixed results rising from concerns for the amount of content provided for the price.[25]

[edit] PC game development

Game development, as with console games, is generally undertaken by one or more game developers using either standardized or proprietary tools. While games could previously be developed by very small groups of people, as in the early example of Wolfenstein 3D, many popular computer games today require large development teams and budgets running into the millions of dollars.[26]

PC games are usually built around a central piece of software, known as a game engine,[27] that simplifies the development process and enables developers to easily port their projects between platforms. Unlike most consoles, which generally only run major engines such as Unreal Engine 3 and RenderWare due to restrictions on homebrew software, personal computers may run games developed using a larger range of software. As such, a number of alternatives to expensive engines have become available, including open source solutions such as Crystal Space, OGRE and DarkPlaces.

[edit] User-created modifications

The multi-purpose nature of personal computers often allows users to modify the content of installed games with relative ease. Since console games are generally difficult to modify without a proprietary software development kit, and are often protected by legal and physical barriers against tampering and homebrew software,[28][29] it is generally easier to modify the personal computer version of games using common, easy-to-obtain software. Users can then distribute their customised version of the game (commonly known as a mod) by any means they choose.

The inclusion of map editors such as UnrealEd with the retail versions of many games, and others that have been made available online such as GtkRadiant, allow users to create modifications for games easily, using tools that are maintained by the games' original developers. In addition, companies such as id Software have released the source code to older game engines, enabling the creation of entirely new games and major changes to existing ones.[30]

Modding had allowed much of the community to produce game elements that would not normally be provided by the developer of the game, expanding or modifying normal gameplay to varying degrees. Arguably, the most notable example is Counter-Strike, a mod for Half Life. Counter-Strike turned the initial adventure FPS into a round based, tactical FPS.

[edit] Distribution

[edit] Physical distribution

Computer games are typically sold on standard storage media, such as compact discs, DVD, and floppy disks.[31] These were originally passed on to customers through mail order services,[32] although retail distribution has replaced it as the main distribution channel for video games due to higher sales.[33] Cassette tapes[34] and different formats of floppy disks were initially the staple storage media of the 1980s and early 1990s, but have fallen out of practical use as the increasing sophistication of computer games raised the overall size of the game's data and program files.

The introduction of complex graphics engines in recent times has resulted in additional storage requirements for modern games, and thus an increasing interest in CDs and DVDs as the next compact storage media for personal computer games. The rising popularity of DVD drives in modern PCs, and the larger capacity of the new media (a single-layer DVD can hold up to 4.7 gigabytes of data, more than five times as much as a single CD), have resulted in their adoption as a format for computer game distribution. To date, CD versions are still offered for most games, while some games offer both the CD and the DVD versions.

[edit] Shareware

Shareware marketing, whereby a limited or demonstration version of the full game is released to prospective buyers without charge, has been used as a method of distributing computer games since the early years of the gaming industry and was seen in the early days of Tanarus as well as many others. Shareware games generally offer only a small part of the gameplay offered in the retail product, and may be distributed with gaming magazines, in retail stores or on developers' websites free of charge.

In the early 1990s, shareware distribution was common among fledging game companies such as Apogee Software, Epic Megagames and id Software, and remains a popular distribution method among smaller game developers. However, shareware has largely fallen out of favor among established game companies in favour of traditional retail marketing, with notable exceptions such as Big Fish Games and PopCap Games continuing to use the model today.[35]

[edit] Online delivery

With the increased popularity of the Internet, online distribution of game content has become more common.[36] Retail services such as Direct2Drive and Download.com allow users to purchase and download large games that would otherwise only be distributed on physical media, such as DVDs, as well as providing cheap distribution of shareware and demonstration games. Companies such as Real Networks provide a service that allows other websites to use their game catalog and ecommerce backend to publish their own game download distribution sites. Other services, allow a subscription-based distribution model in which users pay a monthly fee to download and play as many games as they wish.

The Steam system, developed by Valve Corporation, provides an alternative to traditional online services. Instead of allowing the player to download a game and play it immediately, games are made available for "pre-load" in an encrypted form days or weeks before their actual release date. On the official release date, a relatively small component is made available to unlock the game. Steam also ensures that once bought, a game remains accessible to a customer indefinitely, while traditional mediums such as floppy disks and CD-ROMs are susceptible to unrecoverable damage and misplacement. The user would however depend on the Steam servers to be online to download its games. According to the terms of service for Steam, Valve has no obligation to keep the servers running. Therefore, if the Valve Corporation shut down, so would the servers. However, they have stated that if the service was to be discontinued, games would no longer require authorization from the servers to run. Nevertheless, they are not obligated to do so.

[edit] PC game genres

The real-time strategy genre, which accounts for more than a quarter of all PC games sold,[1] has found very little success on video game consoles, with releases such as Starcraft 64 failing in the marketplace. Real-time strategy games tend to suffer from the design of console controllers, which do not allow fast, accurate movement.[37]

[edit] PC gaming technology

[edit] Hardware

Modern computer games place great demand on the computer's hardware, often requiring a fast central processing unit (CPU) to function properly. CPU manufacturers historically relied mainly on increasing clock rates to improve the performance of their processors, but had begun to move steadily towards multi-core CPUs by 2005. These processors allow the computer to simultaneously process multiple tasks, called threads, allowing the use of more complex graphics, artificial intelligence and in-game physics.[21][38]

Similarly, 3D games often rely on a powerful graphics processing unit (GPU), which accelerates the process of drawing complex scenes in realtime. GPUs may be an integrated part of the computer's motherboard, the most common solution in laptops,[39] or come packaged with a discrete graphics card with a supply of dedicated Video RAM, connected to the motherboard through either an AGP or PCI-Express port. It is also possible to use multiple GPUs in a single computer, using technologies such as NVidia's Scalable Link Interface and ATI's CrossFire.

Sound cards are also available to provide improved audio in computer games. These cards provide improved 3D audio and provide audio enhancement that is generally not available with integrated alternatives, at the cost of marginally lower overall performance.[40] The Creative Labs SoundBlaster line was for many years the de facto standard for sound cards, although its popularity dwindled as PC audio became a commodity on modern motherboards.

Physics processing units (PPUs), such as the Nvidia PhysX (formerly AGEIA PhysX) card, are also available to accelerate physics simulations in modern computer games. PPUs allow the computer to process more complex interactions among objects than is achievable using only the CPU, potentially allowing players a much greater degree of control over the world in games designed to use the card.[39]

Virtually all personal computers use a keyboard and mouse for user input. Other common gaming peripherals are a headset for faster communication in online games, joysticks for flight simulators, steering wheels for driving games and gamepads for console-style games.

[edit] Software

Computer games also rely on third-party software such as an operating system (OS), device drivers, libraries and more to run. Today, the vast majority of computer games are designed to run on the Microsoft Windows family of operating systems. Whereas earlier games written for MS-DOS would include code to communicate directly with hardware, today Application programming interfaces (APIs) provide an interface between the game and the OS, simplifying game design. Microsoft's DirectX is an API that is widely used by today's computer games to communicate with sound and graphics hardware. OpenGL is a cross-platform API for graphics rendering that is also used. The version of the graphics card's driver installed can often affect game performance and gameplay. It is not unusual for a game company to use a third-party game engine, or third-party libraries for a game's AI or physics.

[edit] Multiplayer

[edit] Local area network gaming

Multiplayer gaming was largely limited to local area networks (LANs) before cost-effective broadband Internet access became available, due to their typically higher bandwidth and lower latency than the dial-up services of the time. These advantages allowed more players to join any given computer game, but have persisted today because of the higher latency of most Internet connections and the costs associated with broadband Internet.

LAN gaming typically requires two or more personal computers, a router and sufficient networking cables to connect every computer on the network. Additionally, each computer must have a network card in order to communicate with other computers on the network, and its own copy (or spawn copy) of the game in order to play. Optionally, any LAN may include an external connection to the Internet.

[edit] Online games

Online multiplayer games have achieved popularity largely as a result of increasing broadband adoption among consumers. Affordable high-bandwidth Internet connections allow large numbers of players to play together, and thus have found particular use in massively multiplayer online role-playing games, Tanarus and persistent online games such as World War II Online.

Although it is possible to participate in online computer games using dial-up modems, broadband internet connections are generally considered necessary in order to reduce the latency between players (commonly known as "lag"). Such connections require a broadband-compatible modem connected to the personal computer through a network interface card (generally integrated onto the computer's motherboard), optionally separated by a router. Online games require a virtual environment, generally called a "game server". These virtual servers inter-connect gamers, allowing real time, and often fast paced action. To meet this subsequent need, Game Server Providers (GSP) have become increasingly more popular over the last half decade. While not required for all gamers, these servers provide a unique "home", fully customizable (such as additional modifications, settings, etc.) - giving the end gamers the experience they desire. Today there are over 510,000 game servers hosted in North America alone.[41]

[edit] Emulation

Emulation software, used to run software without the original hardware, are popular for their ability to play legacy video games without the consoles or operating system for which they were designed. The operating system emulators include DOSBox, a DOS emulator which allows playing games developed originally for this operating system and thus not compatible with a modern day OS. Console emulators such as NESticle and MAME are relatively commonplace, although the complexity of modern consoles such as the Xbox or PlayStation makes them far more difficult to emulate, even for the original manufacturers.[42]

Most emulation software mimics a particular hardware architecture, often to an extremely high degree of accuracy. This is particularly the case with classic home computers such as the Commodore 64, whose software often depends on highly sophisticated low-level programming tricks invented by game programmers and the demoscene.

[edit] Controversy

PC games have long been a source of controversy, particularly related to the violence that has become commonly associated with video gaming in general. The debate surrounds the influence of objectionable content on the social development of minors, with organisations such as the American Psychological Association concluding that video game violence increases children's aggression,[43] a concern that prompted a further investigation by the Center for Disease Control in September 2006.[44] Industry groups have responded by noting the responsibility of parents in governing their children's activities, while attempts in the United States to control the sale of objectionable games have generally been found unconstitutional.[45]

Video game addiction is another cultural aspect of gaming to draw criticism as it can have a negative influence on health and on social relations. The problem of addiction and its health risks seems to have grown with the rise of Massively Multiplayer Online Role Playing Games (MMORPGs).[46] Alongside the social and health problems associated with computer game addiction have grown similar worries about the effect of computer games on education.[47]

[edit] Computer games museums

There are several computer games museums around the world. In 2011 one opened in Berlin, a computer game museum that documents computer games from the 1970s until today.

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