I don't claim final authority, but here are what have emerged as the most commonly recommended procedures. On and off. Turn on your PC when you begin computing on any given day, and don't turn it off until you finish for the day, unless you need to keep it on all the time.
Some people turn their computers on and off throughout the day.
This causes a PC's innards to frequently expand and contract, creating stress that can lead to premature component failure. The operating systems of typical PCs and Macintoshes scatter file fragments over the hard disk. Programs such as the Norton Utilities combine these fragments, reducing hard-drive wear and tear and increasing system performance. Some programs signal you to defrag when your hard disk reaches a specified level of fragmentation, such as 90 percent. Alternately, you can defrag weekly, monthly or semiannually, depending on how often you use your machine.