I have acquired an HP X4000 workstation which appears to use the Tyan Thunder i860 S2603 motherboard with a 4 slot memory extension board. The problem is that only certain RDRAM sticks seem to work in this system (strangely enough they seem to be the HP branded memory). Other PC800-45 ECC memory is either not recognized or in the case of the Kensington memory shipped in the system, only 1/2 of the stated memory size is seen (i.e. , a 256mb stick is seen only as a 128mb stick). Internet searches have not been particularly fruitful, other than finding a list of about 1/2 dozen recommended types on the Tyan website. Since I was always under the impression that one PC800 ECC RDRAM stick was the same as any other, I am a bit puzzled. Can anyone reduce my state of ignorance here?