Memory is the thinking space for the PC. The more memory, the more room to think and the faster the PC will perform.
This is one of the major factors affecting overall performance of a PC in business use. It is also one of the obvious places to cut costs in order to produce a budget PC. You should go for as much main memory as you can afford. 512 MB should be your minimum but expect 1 GB in a mid-sized PC and laptop.
Most PCs come with very large disks that have far more capacity than you would need in normal business use. Look for more than, say, 80Gb.
You can usually upgrade laptop main memory by simply plugging in a new module in a hatch in the laptop casing. Normally there are two slots and memory has to be installed in equal sizes. So, if you have 512MB installed in one slot, you are probably restricted to adding just 512MB more without replacing the existing memory. Some 512MB budget PCs come with no slots free. You should expect a 1GB mid-sized laptop to have at least one memory slot free.
Source:
Buying a PC
The Business IT Guide enables businesses to make the right IT decisions