Your question is open ended. There are literally hundreds of factors if not thousands depending on whether for home or business, area of IT you are interested in, size of the computer system, number of users, operating system, ...
I know you do not get much room to state what the situation is. Respond to this answer and you can give a complete or much more complete description of the problem.
Some things to provide are:
What computer system are you working on (hardware)
What is the operating system
What type work would you be doing (network, programming, data entry, security, database management, ...)
How many users are on the computer concurrently
Data storage device types
Peripherals you expect to interact with
Software you expect to interact with
anything else you can think of to tell us such that we can answer without writing an answer literally as long as an encyclopedia set.