Hi ther I have the same model A115, though just replacing it with A2159HP model. Max ram is 1 gb, unfortunately Sony always fill both memory slots with the lower dinominator ie; 2x 256mb units, It becomes a problem when you want to upgrade to 1gb ram, you basicaly have to throw both 256mb modules away and replace with 2x 512mb modules. I can't see why they do not fill only one of the available slots with a 512 and make it much more friendly when one wants to upgrade the ram, it is obviously cheeper for Sony & other to do it this way. The model letters: B, S, K, Z etc relate to the specific purpose of that maching ie; portable. extrem portable, lightweight, desktop replacement etc see vio-link and go to category, computers / VAIO Notebooks then select either ultra mobile or mobile performance, you'll see all the models listed.
