WOW! {Or Holy whatever}

[youshi10 at u.washington.edu]

On Thu, 10 May 2007, Tom Evans wrote:

> On Thu, 2007-05-10 at 08:49 -0700, Garrett Cooper wrote:
>> A good rule of thumb: Don't buy a video card with more RAM than 1/8 to
>> 1/4 of the system RAM, because the RAM is shared with the system RAM,
>> which means you have less overall system RAM to use for apps.
>>
>> -Garrett
>
> Er? Whilst I agree with the sentiment (low end graphics cards with 512MB
> of RAM are solely there to rip off the unwary), that is complete tosh.
>
> Some cards dont have much/any onboard dedicated RAM; instead they use
> system memory. Examples of these are nvidia cards labelled 'TC' (Turbo
> Cache), most (all?) integrated intel video chipsets.
>
> The other issue is on i386. 32-bit systems have 4GB of address space to
> use. Since you want to be able to address the graphics cards memory,
> some of this address space is allocated so the OS can address the
> memory. This means that if system RAM + video RAM > 4 GB, some of the
> system RAM is unaddressable. That itself is a bit simplistic (its not 4
> GB, its ~3.5 GB, for various reasons.)
>
> The main point is that if you have a system with 1 GB of system RAM and
> put in a graphics card with 640 MB of video RAM, you still have 1 GB of
> system RAM to play with, even though you have gone over 1/4 of the
> system RAM.
>
> Tom

Assumption:

( System memory < 2 GB ) & ( Card is AGP ).

I think Robert is correct because AGP needs DMA whereas (and I'm not 100% on this point) PCI-e doesn't.

Most of the statement above was based on DMA and preallocated memory provided to the video card.

-Garrett