I have 1GB currently. I had a situation recently..
Giga 2.5 is loaded, Sonar is loaded. I'm using all 16 channels in port 1 of Giga, and a few channels in port 2. Sonar has Stormdrum loaded into it. I try to load up the Bosendorfer Imperial Grand: out of memory. WHAT? I see only 680MB in use though! I quit Sonar, figuring Stormdrum was eating up RAM. THEN I load the piano, loads fine. I load up Sonar and load my piece, everything loads up fine.
Why is this happening? I'm not even consuming 800MB of RAM yet, and I have the piano loaded, Stormdrum, and everything else. Is it time for me to buy another 1GB of RAM? Or should I ditch Giga 2.5 and upgrade to Giga 3?
Get the additional 1 gig of ram because you will be able to load over 1 gig of instruments in either 2.5 or 3.0. I would get 3.0 because it's more effeciant with ram (if you save your instruments as GS3 instruments) and a more stable program. Read the clean uninstall information at the Tascam site before installing GS3.
The VSL Forum Gigastudio area has a sticky on the registry tweaks.