Type the information into the page at the following link. It will tell you what fits. Buy it from them for a guaranteed working memory module upgrade.http://www.crucial.com/usa/en/advisor
Azrial's posts list specific modules that he got to work. If you buy the EXACT same module it SHOULD work. No guarantees as 4gb is maximum Panasonic recommends. http://forum.notebookreview.com/threads ... 813/page-3
Unless you run 20 windows open at once or are making huge CAD drawings, Use Windows 7 32bit
. 4gb of ram will be more than enough for 32bit windows. And 32bit is more than enough for 95% of Toughbook users.
Buying (2) 4gb modules will cost $120.00 or more used on ebay. For that large of an investment, you would be much better off to put that money towards a CF 31 mk1 instead.
Others have used the 850 evo with successhttp://forum.notebookreview.com/threads ... ad.725310/