1G8, Promise PDC20267 PCI IDE RAID controller. 1999 copyright date on the die.
Looks like they may have been I/O limited on die size? It's hard to tell with the filler metal but it looks like the inner square block has all of the logic. The two big curved traces coming in from the bottom are probably core power and ground, then at the top left is an analog block (likely a dual PLL).
Would need to delayer but I don't think there's anything in the rest of the die. They probably just couldn't fit all of the I/Os needed for several channels of IDE plus PCI into a smaller die area.