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A computer is composed of instructions one can not touch (software), and physical components one can touch (hardware). There is also a cross between hardware and software called firmware.

A computerís hardware is made up of its physical components, like circuit boards, cables, connectors, disks, and peripherals. Software requires hardware to operate and perform logic for it. Software sends instructions to the hardware, which processes the information and returns it. Instructions received by the hardware may be sent to memory, or to the CPU (central processing unit), where it is processed. In the CPU, logic is applied under the direction of the control unit. A typical computer performs several million instructions per second (mips).

Software is a series of instructions loaded into a computerís memory that tell the computer what to do. Three types of software are system, applications, and games and learning software. System software controls computer operation. For example, DOS (disk operating system) and Windows are two types of system software. These programs are stored on disk and control the execution of other software. Application software performs specific tasks, such as word processing, accounting, or creating calendars. It can be bought and used directly or used to compile your own programs. Games and learning software can be used for entertainment or acquiring knowledge.

Firmware is software contained in the hardware. Programs are stored in read-only memory (ROM) so the computer can access it on boot-up. The software may be stored in the hardware on a permanent basis. During startup procedures the computer performs POST (power-on self-tests) to make sure all hardware is accounted for. It also initializes starting addresses and the interrupt handler program. Then it checks the Master Boot Record to determine which disk operating system it should load. This startup procedure is stored in the BIOS (basic input/output system) firmware routine.


Upgrading and Repairing PCs Scott Mueller

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