When talking out of computers,there are two terms which must be correctly distinguished , hardware and software .copmputr hardware refers to all the physical devices in the computer like the CPU the monitor andv the printer that can be physical felt . soft6ware ia all of the instruction that a computer uses to do what you ask it to pieces of softwate are often called programs and an operayting system is a large program that helps all the other programs run.
Modern digials computers are also conceptually similar regardless nevertheless they can be divided into several category on the basics of cost and performances the personal computer or microcomputer a relatively low-cost machine , usually of desktop size (though “laptops are small enough to fit in the briefcase and palm top can fit the pocket ) the workstation, a microcomputers with enchance graphics and communication capabilities that makes it especially useful for office work, the minicomputer , generally too expensive for personal use , with capacities suited to a business , school, or laboratory, and the mainframe computers , a alarge , expensive machine with the capability of serving the needs of major business enterprize , goverments department scientific research establishments or the like ( the largest and fastest of these are called supercomputers)….
The physical component of computer is referred to as the hardware (the hardware describes the physical aspects of computer and related devices.)
The system unit: is the actual computer ; everything else is called a peripheral device your computers system unit probably has at least one floppy disk drive and one CDs, there is another disk drive called the hard disk inside the system unit as known in figure 2.you can not remove that disk or even see it, but it is there in addition `, everything that is currently” in your computer” is actually stored on that hard disk ( we know this because there is no place else inside the computer where you can store information!)
A digital computer is not a single machine rather , it is system composed of five distinct elements;
1. A central processing Unit
2. Input devices
3. Memory storagedevices
4. Output devices
5. A communication network, called a bus which links all the elements of the system and connect the system to the external world.