I am upgrading a desktop for a small non-profit company that contains an Intel D915GAG motherboard (being used as a file server). I updated the BIOS (version 0482), and installed a Pentium 4 620 processor and 4GB RAM. The computer works fine but the BIOS reports that the processor has a 1MB L2 cache but the 620 has an 2MB cache. I went to the Intel website and looked up the compatible processors; interestingly enough the 620 was not on the list but many of the other 6xx processors were there (630, 640, 650, 660, 670). All of the 6xx processors have 2MB L2 caches so it would appear that the BIOS can correctly identify a 2MB L2 cache. Two questions:
The problem you are reporting is very much likely because the processor is not supported by the BIOS, as you have discovered. The processor my work, to a degree, but be prepared for sporadic errors/issues, including the L2 cache being misreported.
Your best approach is to get one of the supported processors.
Also, this board is probably 12 years old. It is long past its life. I would not be surprised if the board started exhibiting signs of failure.
It is also possible that the BIOS simply has a bug and is incorrectly identifying the L2 cache size. I have seen this more than once - and not simply because this isn't a processor on the support list. If you are running on the latest BIOS release (though that's a relative term for a 12-year old board ), then there are no BIOS releases available with this fixed - nor will there for a board that was end-of-lifed so long ago. Does this affect operation? Unlikely. Does this affect performance? No.