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SubjectRe: useful ram on voodoo(2) cards?
On Thu, 17 Dec 1998, Jon M. Taylor wrote:

>> > It probably can't even be used as fast swap. I suggested such an
>> >idea in the old GGI FAQ, and someone later told me that the VRAM+memory
>> >controller logic on standard video cards is designed around the assumption
>> >that writing to video memory will happen much, much more often than reading
>> >from video memory. I don't remember the particulars, but the upshot is that
>> >bandwith reading from VRAM is maybe 1/4 of bandwidth writing to VRAM. As
>> >such, VRAM reads will be so much slower than VRAM writes that any gains you
>> >might have gotten from the extra RAM evaporate. If you have "normal" VRAM
>> >I/O and maybe accels and DMA too (i.e. something is actually using the video
>> >card for its intended purpose) going on simultaneously the situation gets
>> >even worse.
>> Are you saying that swap to VRAM would be slower than swap to
>> hard disk?
> No. I am saying that you'd better not be wanting to do any
>serious video work with the video card if you do use it for swap. And
>normal system [S]DRAM is cheaper and sits on a faster bus with no
>contention from other I/O devices.

The presumption is that someone has a 3dfx card with RAM on it,
that is *NOT* being used for video, and that as such there is
wasted resources in the machine. Thus using those resources is
definitely going to be better than not using them assuming that
there are no technical reasons why it can't be used as such.

> AGP and/or UDMA architectures will
>render this idea obsolete anyway.

I don't understand how. Will hard disks become faster than video
memory? If so, why not put a hard disk on the video card. It
makes 0 sense.

Mike A. Harris - Computer Consultant - Linux advocate

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