I've had a very difficult time adding two memory chips to my SONY VAIO VGC-RA820G desktop. The machine has 2 500MB chips and there are two more sockets available for two more 500MB chips. The machine maximum is 2Gig.
I have already ordered and returned from 4 different vendors
INFINEON HYS64D64320HU-5-C 500MB
chips which the vendors claimed would be compatible with my computer. They are not.
The machine would not boot. (The BIOS is up-to-date and I have tried all combinations chips in different sockets.)
The original chips in the machine are labeled