First, remove the casing of the computer. Make sure you have the anti static wristband on and the alligator clip tightly fastened to the computer case to avoid a static discharge. There are typically four screws in the back thin metal panel to be removed allowing the metal casing to slide free from the tower. In newer computers such as Mac, HP, Compaq, Gateway, and Dell there are two screws on one side of the tower at the rear that will allow the side panel to be removed for access to the motherboard and other internal components.

The second step is to locate the card to be replaced or installed. This is most easily accomplished by looking for the card in the rear of the computer such as a video card or modem then sliding your hand around to the inside of the case to assure you have the correct card. Then removing the one screw in the thin metal strip holding in the card.

The third step is to place the tower on its closed side down. Now put one hand on the metal strip of the card and the other hand on the end of the card. Apply steady pressure up to disengage the card from the motherboard slot. This is not complicated and computer cards are relatively strong.

For the fourth step unwrap the new card from the plastic static resistant packaging. Hold the card in the same manner you removed it and line it up with the motherboard slot making sure the line in the center of the card lines up. Most newer computer card boxes will have a sticker on the side telling the consumer what type the card is PCI, AGP, or PCI Express. When you are satisfied the card matches the motherboard slot apply gentle steady pressure straight down, this is important to insure you do not bend the metal strip or break the sensitive contacts on the card itself.

For the fifth and final step, replace the screw you removed in step two to the metal strip of the card and the computer case. Now replace the side or rear panel of the case and the case screws. Stand your computer in the up right position and press the power button, making sure it doesn't make an unusual beeping or thumping noise and boots to your operating system. Insert the software disk that came with your new card and follow the onscreen instructions.

Congratulations, you have successfully installed your first computer card and saved some money to boot. Showcase your talents next time someone needs a card replaced and make a little money for your very hard work and time.

Introducing Direct Memory Access - DMA

Optimizing CPU time and making the most out of what you've got with the least amount of effort and expenditure. These are the objectives of many technologies including Direct Memory Access (DMA).

So what is DMA?

Direct Memory Access or DMA is a process whereby data is moved from a device such as a hard disk drive into system memory without the direct control or indeed any other involvement on the part of the Central Processing Unit - CPU. This "frees` the CPU to do other tasks. However; before we can begin to understand DMA and its implications we need to take a short trip down memory lane in order to give the entire subject some perspective.

Back in the good old days when PCs were young the CPU really did do it all. Every process that took place in a computer happened under the direct watchful scrutiny of the CPU. Nothing happened unless the CPU was involved. The CPU ran all programs and took responsibility for the transfer of data from point A to point B as well as to and fro from peripherals.

This meant that while the CPU was engaged in these menial tasks it could not be used for anything else. Attending to purely data transfers was a big waste of resources and the machines of the day were most definitely not over-endowed on the resources side of things.

Well it wasn't too long before IBM's engineers realized that they should be able to get a major performance boost from the hardware they already had simply by working "smarter`. Their research had shown that it is more efficient to have peripheral devices look after their own transfers rather than the CPU. Let us take a quick look at how this can happen by examining the print process:

• The CPU dumps data to a set range of addresses in system memory, initiates the transfer of the data through the traces on the motherboard to the correct interface port and on to the print device
• With this done the CPU is quite satisfied that it has completed its task and the print job has been printed
• In reality however; nothing could be further from the truth because the CPU along with the rest of those components that were involved in transmitting the print job data actually sent the print job data to the print device at a rate which far exceeds the maximum printing speed of the device
• What is really taking place is the print device (or even a print server) has accepted the print job data as fast as it could receive the data, placed it into a temporary holding memory (printer cache memory) and placed the request to print at the end of its jobs-to-do list (print queue)
• If already engaged in printing another job the printer continues printing that job until it has been completed. It then moves to the print job at the top of its print queue and prints that. Eventually the printer will get to our job and print it.
• In the meantime the CPU has been on a quick world tour courtesy of the Internet, played some music and done a whole bunch of other tasks that the user requested

The lesson to be learned here is that had the CPU only been able to send the data at a rate equal to the printer"s maximal printing speed it would have been tied up doing so for the duration of the printing process and most certainly would not have played the music, surfed the net or done anything else.

So what actually took place was that the CPU dumped the print job into memory, notified the printer that a job was ready and went off to have some fun leaving the printer and print device to handle the actual printing process and even the transfer of the data to be printed from memory to the printer's own cache memory and all at a speed that the printer was comfortable with.

It is the methodology of permitting the end device to control the transfer of data intended for its self that is known as Direct Memory Access - DMA and it is bi-directional procedure. This means that in the event of another peripheral device having a task that the CPU must perform the peripheral device will transfer its job into system memory and once done send a message to the CPU informing it that there is now a job in memory ready to be executed.

In summary we now have a system whereby end devices can receive data from system memory of transfer it into system memory (RAM - Random Access Memory) and all without any help or direct guidance from the CPU.

DMA Controllers

We all know that for any process such as the one that I have just outlined above something somewhere must be orchestrating the affair. First of all a whole bunch of additional traces (wires embedded into a PCB) were built into motherboards. Some were devoted to controller functions and others were dedicated to the actual data transfers.

At first this was an add-on or expansion card which in time became integrated into silicon and embedded into the motherboard and then finally absorbed into the motherboard's chip set support capabilities which is where it has remained to this very day.

The other half of the system also needed the same supporting controllers and devices such as hard disk drives underwent the same integration process as the motherboard and so their side of the DMA has been absorbed by integrated controllers built into the drives supporting silicon and the controlling logic is now part of the devices firmware.

Implementing DMA

Here are the system requirements for DMA to work. You need:

• Peripheral devices such as a hard disk drive or optical disk drives that support DMA
• A motherboard which supports DMA
• An operating system and specialty applications that comply with the DMA standards specifications
• A motherboard system BIOS that supports DMA functionality as well

Note:

• DMA channels are to be found on the ISA bus & its derivatives EISA & VLB
• PCI devices do not use standard DMA channels at all

Third-Party DMA Bus Mastering

Standard DMA is also known as "third party" DMA meaning that the system DMA controller is actually doing the transfer and the first two parties are the sender and the receiver of the transfer.

First-Party DMA Bus Mastering

Here we have the peripheral device that is doing the transfer actually taking over control of the system bus to perform the transfer.

• This is also called bus mastering and provides much better performance than regular DMA because modern devices have much smarter and faster DMA circuitry built into them than what exists in the older standard ISA DMA controller
• Newer DMA modes; such UDMA - Ultra DMA (mode 3 or DMA-33) are now available and they provide much faster transfer rates

Limitations of Standard DMA

While DMA provided a significant improvement over CPU controlled data transfers, it too eventually reached a point where its performance had become a limiting factor.

• DMA on the ISA bus has been stuck at the same performance level for over 10 years
• For old 10 MB XT hard disks, DMA was a top performer

PCI Bus

As computers evolved the PCI bus was introduced by Intel® and hard disk drives capacities started to get large and continue to do so. But a few years back HDD capacities started to exceed 80 GB and the drive itself was capable of transferring data at many megabytes per second standard DMA was not able to keep up to the task and had become more of a mill stone than a plus. This was when we started to see new technologies come into being in the mass market including:

• PIO - Programmed I/O or 1st Party DMA bus mastering on the PCI bus to control hard drives as opposed to using the standard ISA DMA that was used for devices like sound cards. This freed these drives from the older ISA DMA controllers which meant that they could access the bandwidth they need for optimal performance.
• Over the next couple of years many of the devices that used to use DMA on the ISA bus jumped ships and were now using PCI bus. Mastering over the PCI bus meant far superior performance. Some of these devices were: new high-end SCSI cards, Network Interface Cards, Video Cards and many more.

DMA Controllers

For those who are serious about passing their A+ certification exam here is a list which you are bound to get a couple exam questions about:

• On new PCs the standard DMA controller has been integrated into the system chipset
• The original PC & XT had one of these controllers that supported 4 DMA channels, 0 to 3
• With IBM's launch of the AT form factor a 2ND DMA controller was added
• To ensure backwards compatibility and greater uniformity the IBM design engineers decided to use the same cascade technique employed with the introduction of the 2ND IRQ controller to cascade the 1ST DMA controller to the 2nd DMA controller
• The big difference here though was that where the 2ND interrupt controller is cascaded to the 1ST interrupt controller the exact opposite is the case for the 2 DMA controllers. With the 1ST DMA controller cascaded to the 2ND
• The result is that although there are 8 DMA channels numbered 0 to 7, DMA 4 is not usable
• There is no rerouting as was the case with IRQ2 and IRQ9
• All of the original DMA channels (0 to 3) are still usable directly

DMA Channels and the System Bus

• Except for DMA 4 all other DMA channels are available to devices on the ISA system bus because channel 4 is used to cascade the 2 controllers together
• PCI devices do not use any of these standard DMA channels
• The 2ND DMA controller was added when the ISA bus was expanded to 16-bit with the introduction of the AT
• The traces to access these extra DMA channels were incorporated into the extra part of the expansion slot on the model AT PC and so only 16-bit devices can access the extra DMA channels (5,6,7)

2 Signals/DMA Channel

1. DRQ - DMA Request
2. DACK - DMA Acknowledgment

Some peripheral cards have separate jumpers for these instead of a single DMA channel jumper so ensure that the DRQ & DACK are set to the same number, otherwise the device won't work

DMA Details Summary

• DMA channels 0-4 which were originally 8-bit had a maximum of 64KB per transfer
• Then starting with the AT 0, 5, 6 and 7 were 16-bit channels capable of 128KB per transfer but still only one transfer at a time
• DMA must reside in conventional memory and not many ISA based cards could take advantage of the new DMA channels
• DMA channel 3 is the one most likely to experience conflicts resulting in very strange and erratic behaviour
• Although DMA was standardised at this point PCI does not use DMA in the same way as the other expansion bus slots. Instead PCI usually implements DMA as bus mastering with the device taking control of the bus

Here is a list of Ati and nVidia distributors, as well as a breif description of each.

Ati nVidia

• MSI
• PNY
• HIS
• Sparkle
• Ati
• XFX
• EVGA
• Foxconn
• MSI
• Gigabyte

All of these are good brands to buy. Ati on the Ati side, as well as the others have excellent products and customer support. All Nvidia brands listed are good, Foxconn is a newer company that shows promise. XFX makes the best cards, but has horrible customer support. A good solid brand on the nVidia side is eVGA (also the biggest).

Nvidia cards follow different architectures depending on the version of DirectX that was cureent when they were released. For example, an 8600 card and a 7600 card may be almost the same, but the 7600 runs on the older DX9 architecture, and the 8600 runs on the DX10 architecture. This is a good guide to nVidia card models based on what you'll use them for.

• Home use - FX5200, 5300, 5600, 6100
• Workstation - Quadro 440, Quadro NVS 55
• Gaming- 6800, 7300GT, 7600GS, 7600GT, 7800GT/GS, 7900GT/GS, 8600GT, 8500
• High-End Workstation - Quadro FX Series, Quadro FX 4600, Quadro FX 4500
• Ultimate Gaming - 7950GT, 8800GT, 8800GTS, 8800GTX, 8800 Ultimate

Ati cards follow much the same pattern. They run a little pricier and tend to be of equivalent quality. If you find a good deal on an Ati card, get it. In general, though, I would stick to nVidia.

• Home use - Radeon 9250, Radeon 9550
• Workstation - FireGL V3100, FireMV 2200, FireGL V3300, FireGL V3400
• Gaming - X1300 pro, X1600 pro, X1650 pro, X1950 Pro
• High-End Workstation - FireMV 2400, FireGL V5200, FireGL X3, FireGL V7300, FireGL V7350
• Ultimate Gaming - Radeon HD 2900XT

You may be wondering, what's the difference between a gaming and a workstation card? Well, gaming cards are designed to handle everything that you would come across in a game; things like rendering, physics, numbers of polygons, etc. Workstation cards are made to help the CPU by handling many operations simultaneously. Workstation cards can handle many displays and many mathmatic calculations.

What about SLi and Crossfire then? Well, both are technologies used to run 2 or more video cards at once through the PCI-Express slot located on your motherboard. Both double your cards power. SLi is made for nVidia cards and Ati has Crossfire.

There are three different busses that your video card can run through. The first is a PCI-E x16 bus. This is characterized by being very thin and is usually either green or white, though it has a couple other colors, and having a nub to hold in your vieo card. There is usually 1-2 of these busses on your motherboard. The second is AGP 8x. AGP 8x slots are usually brown and bulky with little nubs on the end to hold in your graphics card. The last is PCI. Almost every motherboard built in the past 7 years has had at least 1 PCI slot. PCI slots are white and the same width as AGP slots. PCI slots have no nubs to hold in a graphics card. Make sure you get the correct card for your motherboard because they are not interchangeable.

Installing the card is simple enough, I can show it in 5 simple steps:

1. Open your case, touch an unpainted metal surface to prevent static discharge which can harm your computer. If at all possible, don't work on a carpet.
2. Remove your current Video Card (If applicable).
3. Place the new Video card in the approproate slot. Fasten onto the case in the back.
4. Replace cover on your computer. And hook up monitor to the new video card.
5. Boot up and install the driver disc that came with the video card. If there was none then download the drivers from either Ati or nVidia's website.

Well, I think I covered everything that needs to be covered. Have fun!