The addressable amount of RAM....

Usually RAM is not at all a headache for nowadays computers since it is cheaper and comes as a single modules with multy GBs... U dont need to buy 2 RAMs with 1GB each for a total of 2 GB... Instead u will get a 2GB in a single module with a price difference of ~ 500 /- from 1 GB...We usually hear upto 4GB commonly. But dont think that a heavy amount of RAM can boost your system performance to a supersonic speed... Understand the maximum byte addressibility of the operating system that u are going to use before u choose the amount of the RAM...

For instance see the following case...

Usually the operating that we are using in our home or office are 32 bit..The 32bit version of the Windows XP / Vista are mainly used in almost all computers except high-end ones..32 bit versions of Windows vista and XP can address only 3.5K main memory....That is even if u have 4 or 5 or 6 or greater GBs plugged in your system, the opeating system will read only 3.5Gb.... The operating system uses only 3.5 GB out of the 4 or 5 or greater GB of the RAMs...

In this cases, if u see the properties tag of windows u may see only 3.5 GB while ur BIOS shows the correct amount of main memory plugged in...

If u need to make use of the full amount of the RAM, choose to install 64 bit versions of the operating systems which can handle upto 128 GB of the RAM...