Computer system consist of 2 main components:
Hardware-includes all equipment and devices which are making up of electronics, electrical and mechanical components.
Software-consist of system, utilities and application software, which will instruct the hardware to perform the required task.

THE HARDWARE
There are basically 4 main units in a computer:
-> The Input Unit
-> The Central Processing Unit (CPU)
-> The Memory Unit
-> The Output Unit

THE INPUT UNIT - enter data or command
- Keyboard- traditional, flexible, ergonomic, wireless, and PDA
- Scanners- optical scanners (flatbed and portable), bar code readers (scanners), Wand readers or platform scanners

THE CENTRAL PROCESSING UNIT (CPU) - MICROPROCESSOR - The "brain" of the entire system

In a PC, the CPU is a single electronic chip wit three main electronic sections:
-> Arithmetic Logic Unit (ALU) - it does all computations and makes decision
-> Control Unit - controls the operation of the computer system by sending electronic signals
-> Internal Registers - the immediate memory storage within the CPU.

THE MEMORY UNIT

Primary Memory - store data/instruction needed currently by the CPU. Faster access time but expensive.

-> RAM (Random Access Memory) chips are called temporary or volatile storage because their contents are lost if power is disrupted.
- Cache memory or RAM cache is a high-speed holding area for frequently used data and information
- Virtual memory uses the hard disk or run large programs on systems with limited memory
- Flash RAM or Flash Memory is special type of RAM that does not lose its contents when power is disrupted.

->ROM (Read Only Memory) chips, also called firmware. This is permanent memory (i.e non volatile) ans stores programs and information needed by the computer to start up and do the basic routines required for the computer system to function effectively. The programs and data are burned-in to the ROM chip during manufacture.

Secondary Memory - main memory
-> Floppy Disks are known as diskettes, disks, flexible disks, and floppies. Floppy disk drives (FDD) store data and programs by charging disk surface.
- Traditional Floppy Disk - 1.44MB 3 1/2 inch disk. 2DH indicates two-sided high density disk

-> Hard Disks are rigid metallic platters that provide much greater capacity
- Internal Hard Disk (Fixed Disk) are located within system unit and typically identified as the C drive.
- Hard-Disk Cartridge is removable and capacity limited only by the number of cartridges. PC Card had disks are for notebooks.

-> Optical Disks use laser technology. Jewel boxes protect optical disks.
- Compact Discs (CDs) have typical capacity of 650MB to 1GB
- CD-ROM : read only, used to distribute databases. Reference, and software.
- CD-R : known as CD burners; used to create custom music CDs and to archive data.

THE OUTPUT UNIT - display or print processed data on hardcopy
- Printers - Ink-jet printers, laser printers & Thermal printers, dot-matrix printers, plotters, photo printers and portable printers.
- Audio output devices - Speakers and headphones

INPUT AND OUTPUT DEVICES
Many devices combine input and output functions :
- Fax machines
- Internet Telephone
* I/O Interface Card
- All I/O devices required an Interface card placed between Computer system and the peripheral devices, unless it is built in the mother board.

THE SOFTWARE
The 2 categories of software are : systems software and application software.

System program- special-purpose programs designed to meet the needs of the computer system
-Operating system
- a set of routines that direct & manage the operation of the entire computer system. A traffic controller for the computer hardware.
- controls the sharing of the hardware resources: disk, memory and CPU processing times.
- eg: Windows XP, Window 2000, Window 95/98/ME
-Device Drivers
- programs to allow input and output devices to communicate with the rest of the computer system

Application Software- programs that handle the processing for an application
-General-purpose (basic application)
- Program written to perform special function & solve specific problem.
- eg. AutoCAD, MS Word, MS Excel
-Special-purpose (specialized application)
- focus on specific disciplines and occupation
- eg. Programs include graphics, audio and video

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