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[ The PC Guide | Systems and Components Reference Guide | Video Cards | Video Card Performance ]

Bit Width

Most video cards are specified in part by a bit width. It is important not to be mislead by claims from video card manufacturers about how many bits their card "is". Many companies are now coming out with cards that are claimed to be "128 bits" and the implication (or worse, direct statement) is that these are much better than 64 bit cards. This is very misleading for several reasons.

The bit size of a video card usually refers only to one portion of its operation, such as how many bits it uses to access the video memory. Virtually every card, for example, still accesses the PCI or VLB system bus using 32 bits, no matter what the width of the internal processing circuits is on the card. This means a 128 bit card cannot (all else being equal) have double the performance of a 64 bit card. Perhaps more importantly, there are no standard definitions of what exactly a "128 bit card" means. Two different manufacturers can have totally different standards for deciding what is a 64 bit card and what is 128 bits.

A card with a wider internal memory bus can in theory have more performance, but remember that it is just one component in a complex performance equation. Don't be dazzled by the big numbers. A high-quality card that calls itself "64 bits" can be much faster than one calling itself "128 bits" if the former has a better-implemented chipset--or better drivers.

Next: Video Memory

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