I have put 2GB + 1GB of DDR2-667 memory, and it worked just fine. I've tried with 2 x 2 GB, but the laptop couldn't recognize past the 3 GB.
Besides, I suspect that there are implications regarding the video memory allocation, because when I booted into either XP or Ubuntu, the screen went all blank, altough the computer was still responsive. It might be the case of just some tweaking.
I used Kingston memory, with these part numbers:
- 2GB - KVR667D2S5/2G
- 1GB - KVR667D2S5/1G
If anyone managed to make the SI1520 work with two 2Gbs memory modules, please let us know, even if the laptop only recognizes a total of 3Gbs!
In fact, the use of two memory modules of the same type would make a "dual channel" setup, allowing the laptop to access memory much faster, since it would see them as a single 128bit wide memory bank, instead of two 64bit wide banks.
Update 4/18/2009: user neustaedter points out that using Windows Vista 64, the system recognizes all 4Gb. This does not work with BIOS v1.20, and v1.10 needs to be installed.