Options : Enabled, Disabled

This feature is also labelled as SDRAM Page Closing Policy in some BIOSes. This feature determines whether the processor or the SDRAM itself controls the precharging of the SDRAM. If this option is disabled, all CPU cycles to the SDRAM will result in an All Banks Precharge Command on the SDRAM interface which improves stability but reduces performance.

If this feature is enabled, precharging is left to the SDRAM itself. This reduces the number of times the SDRAM is precharged since multiple CPU cycles to the SDRAM can occur before the SDRAM needs to be refreshed. So, enable it for optimal performance unless you are facing system stability issues with this option enabled.

DRAM Data Integrity Mode

Options : ECC, Non-ECC

This BIOS setting is used to configure your RAM's data integrity mode. ECC stands for Error Checking and Correction and it should only be used if you are using special 72-bit ECC RAM. This will enable the system to detect and correct single-bit errors. It will also detect double-bit errors though it will not correct them. This provides increased data integrity and system stability at the expense of a little speed.

If you own ECC RAM, enable it (set ECC) to benefit from the increased data integrity. After all, you have already spent so much for the expensive ECC RAM so why not use it? ;) If you are not using ECC RAM, choose Non-ECC instead.

Read-Around-Write

Options :  Enabled, Disabled

This BIOS feature allows the processor to execute read commands out of order, as if they are independent from the write commands. It does this by using a Read-Around-Write buffer. Writes are accumulated in this buffer and then written to memory as a burst. This reduces the number of writes to memory and boosts the memory's read performance.

In addition, the Read-Around-Write buffer serves as a cache of the most up-to-date data that hasn't been written to memory yet. So, if a read command points to a memory address whose latest write (content) is still in the Read-Around-Write buffer (waiting to be copied into memory), the read command will be satisfied by the cache contents instead.

In short, if the Read-Around-Write buffer has the data, the CPU can directly read off it, without needing to access the memory (which will take more time). This further improves the memory's read performance.

Therefore, it is recommended that you enable this feature.

System BIOS Cacheable

Options : Enabled, Disabled

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

Options : Enabled, Disabled

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

Options : Enabled, Disabled

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. For more detailed information, check out the Video RAM Caching guide.

Memory Hole At 15M-16M

Options : Enabled, Disabled

Some special ISA cards require this area of memory for them to work properly. Enabling this function reserves the memory area for the card's use. In some cases, it may also prevent the system from accessing memory above 15MB.

If you enable this function, 1MB of RAM (the 15th MB) will be reserved and is therefore not available for the OS' use. So, if you have 128MB of RAM, this feature effectively reduces the usable amount of RAM to 127MB.

In certain motherboards, this feature may actually render all RAM above the 15th MB off-limits to the OS! In this case, you will effectively have only 14MB of RAM, irrespective of how much RAM your system actually has.

Since ISA cards are a thing of the past, you should always disable this feature. Even if you have an ISA card that you absolutely must use, that doesn't mean you must enable this feature. Most ISA cards don't need this reserved memory area. Check to make sure that your ISA card absolutely requires this memory area to work properly before enabling this feature.