System/Video BIOS Cacheable (BIOS options)...

[PlunX]

Should these be enabled or disabled? They're disabled by default on my motherboard, but the manual says that enabling them will increase performance but an error might occur if data is written to a certain area of the BIOS or something of that sort. What's the deal with these options?

 

[BadThad]

Enable them both. It's always a good move to cache BIOSes. You won't see any errors, don't worry.

[edit]I stand corrected. Thanks for the info, been a long time since I've been to that site![/edit]

 

[jinsonxu]

I disable them.

Quoted from Bios Optimisation Guide from Rojakpot


System BIOS Cacheable

This feature is only valid when the system BIOS is shadowed. It enables or disables the caching of the system BIOS ROM at F0000h-FFFFFh via the L2 cache. This greatly speeds up accesses to the system BIOS. However, this does not translate into better system performance because the OS does not need to access the system BIOS much.

As such, it would be a waste of L2 cache bandwidth to cache the system BIOS instead of data that are more critical to the system's performance. In addition, if any program writes into this memory area, it will result in a system crash. So, it is recommended that you disable System BIOS Cacheable for optimal system performance.


Video BIOS Cacheable
This feature is only valid when the video BIOS is shadowed. It enables or disables the caching of the video BIOS ROM at C0000h-C7FFFh via the L2 cache. This greatly speeds up accesses to the video BIOS. However, this does not translate into better system performance because the OS bypasses the BIOS using the graphics driver to access the video card's hardware directly.

As such, it would be a waste of L2 cache bandwidth to cache the video BIOS instead of data that are more critical to the system's performance. In addition, if any program writes into this memory area, it will result in a system crash. So, it is recommended that you disable Video BIOS Cacheable for optimal system performance.


Video RAM Cacheable

This feature enables or disables the caching of the video RAM at A0000h-AFFFFh via the L2 cache. This is supposed to speed up accesses to the video RAM. However, this does not translate into better system performance.

Many graphics cards now have a RAM bandwidth of 5.3GB/s (128bit x 166MHz DDR) and that number is climbing constantly. Meanwhile, SDRAM's bandwidth is still stuck around 0.8GB/s (64bit x 100MHz) or at most 1.06GB/s (64bit x 133MHz) if you are using a PC133 system.

Now, although a Pentium !!! 650 may have a L2 cache bandwidth of about 20.8GB/s (256bit x 650MHz), it makes more sense to cache the really slow system SDRAM instead of the graphics card's RAM.

Also note that caching the video RAM doesn't make much sense even with the Pentium !!!'s high L2 cache bandwidth. This is because the video RAM communicates with the L2 cache via the AGP bus which has a maximum bandwidth of only 1.06GB/s using the AGP4X protocol. Actually, that bandwidth is halved in the case of the L2 cache caching the graphics card's RAM because data has to pass in two directions.

In addition, if any program writes into this memory area, it will result in a system crash. So, there's very little benefit in caching the video card's RAM. It would be much better to use the processor's L2 cache to cache the system SDRAM instead. It is recommended that you disable Video RAM Cacheable for optimal system performance.

 

[Mem]

Definetly disable them they were only worth enabling in the old DOS days for slight increase in speed for games,however now cards perform better with video shadow disabled it also can improve stability.