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Buying a Computer

Memory

A stick of ramRandom Access Memory (RAM) is the term used to describe memory found on PCs or graphics controllers (more on this later). Memory is incorporated into a desktop PC via memory modules, which connect through dedicated memory slots on the motherboard.

The most commonly used type of RAM in PCs is Double Data Rate (DDR) SDRAM. Single Data Rate (SDR) SDRAM is still available for older systems is becoming increasingly rare. SDRAM also differs in the physical sense, SDRAM DIMMs will not physically fit into a DDR RAM slot and visa versa. Both are implemented into the system as DIMMs (Dual Inline Memory Modules). DDR memory will always give your system or graphics card better performance than SDR memory. This is because DDR, or double data rate RAM, sends two data bits on every clock pulse. DDR II memory has also been recently released with improved speeds and heat spreaders to keep the memory cool.

DIMMs come in different flavours - PC100 and PC133 for SDRAM, and PC2100, PC2700, PC3200, PC4000, PC4400 for DDR SDRAM. DDR II RAM is also available from PC3200 up to PC6400. The numbers relate to the speed at which the memory modules can operate (although the DDR numbers use a different measuring system, so it is impossible to compare the two types of memory through listed speeds alone). Your motherboard must support the type of memory you want to use. Currently only some Intel boards use DDR2.


Graphics controller

Graphics controllers are the devices that connect to and tell monitors what to display. They also take over many of the processing tasks associated with rendering and displaying 2D and 3D graphics. By taking over many display-related tasks from the CPU, the graphics controller allows the CPU to focus on other tasks without affecting overall system performance. They vary considerably in price and capabilities. You can pay as little as $50 for one, or over $1,000.


Onboard graphic controllers

Not every PC you buy will have a dedicated graphics controller. You will generally find that in small form factor PCs - that is, physically smaller systems - there is not enough space to have a dedicated graphics controller. The normal practice in such a case is to integrate sound and graphics on the motherboard. The end result may be a PC that will only do a portion of the graphical things a PC equipped with the top-of-the-range graphics controller can do.

However, it is also important to note that a regular ATX PC (see 'PC Cases' below) can come with this cut-down graphics component. Once again, you will most likely see this on budget PCs. The quickest way to know is to ask the retailer if it has a separate graphics controller or one integrated on the motherboard.


Which graphic chipset?

Although a large number of manufacturers build graphics cards for PCs, nearly all of them use components from one of two major developers of graphics card chips: NVIDIA and ATI. Cards based on identical graphics chips will be nearly indistinguishable in terms of performance. Matrox is another well-known brand used by video, 2D and 3D graphics professionals. A new player, XGI, is also gaining popularity amongst gamers.

NVIDIA produces graphics controller chips with the GeForce brand. These are divided up into graphics controllers for the budget, mainstream or the higher-end/gaming enthusiasts markets. The latest range of GeForce graphics chips is the 6xxx series, which is now available in a 6800 version for enthusiasts, or in a 6600 version for mainstream systems. There's also a range of chips in the 6200 series for the budget-conscious.

Although the grades of graphics controllers vary, it is quite normal to find features such as TV-out or S-Video on mainstream controllers, without having to pay more for the high-end controllers. For example, consumers can pick up an AGP based 6600 graphics controller with TV out and a DVI port for a little over $200. In comparison, the top of the range PCIe based 6800 controller will set you back around $650 or $520 for an AGP model. The lower-end chips, however, will run slower and may not have the cooling or heatsink features which have been incorporated into the higher-end controllers.

The current range of ATI graphics chips are branded under the Radeon name. Common Radeon chips include the X600 and X700, the X300 for the budget buyer and higher-end users can keep an eye out for chips based on the X850. Prices may vary from $100 for the X300 Radeon to between $160 and $350 for the X600 and X700. The Radeon X850 is bit more expensive with prices close to the $800 mark so it's best to have an idea of just how demanding your system requirements are before deciding on the more expensive option.


Which interfaces do I look out for?

There are two kinds of interfaces in the motherboard used to connect graphics cards: AGP and PCIe. Whatever graphics card you buy, it must match the slot in the motherboard.


AGP An AGP 6600gt

The AGP bus is a dedicated graphics connection used only by an AGP graphics controller. AGP works in various modes. Not all motherboards support all modes.

  • AGP 1X mode (which has a speed of 66MHz and data transfer of 264MBps) is twice as fast as that of PCI (33MHz; 132MBps).
  • AGP 2X mode (133MHz; 528MBps) is four times faster than PCI.
  • AGP 4X (266MHz; 1.02GBps).
  • AGP 8X (533MHz; 2.1GGBps).

Although the capacity of the AGP port will be determined by the main board, it is worth pointing out that graphics cards support certain AGP standards. This means that if you purchase a graphics cards separately to your system, you will need to check the main board is equipped to handle the AGP mode the graphics card works at.


PCI Express

PCI Express or PCIe was ratified in late 2002 to overcome the limitations of AGP. The new interface has a higher bandwidth throughput, lower pin count and lower latency, making it overall the superior choice for graphics. PCIe types can be broken down into four different modes:

  • PCIe 1X mode (500MB/s) uses a single data lane - both directions
  • PCIe 4x mode (1000MB/s) uses a double data lane - both directions
  • PCIe 8X mode (4000MB/s) uses a quadruple data lane - both directions.
  • PCIe 16X mode (8000MB/s) uses 4000MB/s per directions.

Nearly all graphics cards are of the PCIe 16X variety.

A lot of the latest release motherboards feature PCIe slots and are physically incompatible with AGP cards. If you are looking to upgrade to PCIe for improved graphics, don't go and sell your soul just yet. A lot of the games still perform exceptionally well with an AGP based card but if you're after some serious pixel pushing power, PCIe may be worth investigating.


What is RAMDAC

You may come across the term RAMDAC in your shopping. This is an acronym for Random Access Memory Digital-to-Analog Converter. RAMDAC is a chip on graphics controller cards and its role is to convert digitally encoded images into analog signals that can be displayed by a monitor.

RAMDAC speed is a frequency at which the RAMDAC processes the pixels and sends the video signals to the monitor via the VGA connector. Speeds to look out for include a range from 270MHz up to 360MHz. The higher your screen resolution, the higher the RAMDAC speed.


Which memory?

Video cards also contain onboard RAM, which is used as a working space for the graphics operations.

The two graphics memory types you are likely to encounter Single Data Rate (SDRAM) and Double Data Rate (DDRAM) memory. Some of the newer cards also feature DDR-II or graphics DDR (GDDR).

A powerful graphics card will have 256Mb of memory. Low-end cards normally have less RAM, usually of the DDR variety.

   

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