The practical maximum RAM for Intel Core 2 Duo chipsets is 8GB, as User32 noted, and as they also noted, 4GB DDR2 SO-DIMM RAM modules are expensive and often rather hard to find. Service manuals and the like often list 4GB as the maximum RAM because either 4GB sticks weren't available when the specs were written or Intel's marketing materials incorrectly claimed that only 4GB is supported. I currently have 5GB (1+4GB) of RAM installed on my CF-19FHGAXNS; it was quite a performance boost to go from 2GB to 4GB (since Windows XP is a 32-bit OS and thus it cannot even use the whole 5 gigabytes properly). I've been trying to find an affordable 4GB stick so that I could eventually get rid of the 1GB stick, although that's gonna be somewhat annoying since it requires taking the laptop apart. Depending on your financial resources and intended use cases etc. you may indeed want to consider a newer CF-19 which supports DDR3, but if this isn't an option for you, rest assured -- Mk2 CF-19's do support more than 4GB of installed RAM.