A computer is organized into three basic units:
(i) Central Processing Unit
(ii) Memory Unit
(iii) Input/Output Unit
(i) Central Processing Unit (CPU)
CPU is the component of a personal computer system that interprets and performs instructions provided by the software. The Central Processing Unit or CPU, is the most important part of the computer. It is called as the brain of the computer. It makes all the required calculations and processes data. The CPU can be divided into three main components: Arithmetic and Logic Unit, Control Unit and Register.
Arithmetic and Logic Unit (ALU) performs all the mathematical and logical operations on the information supplied to the CPU.
Control Unit (CU) directs the working of the CPU.
Register is a very high speed storage area inside the CPU. The number of registers that a CPU has and the size of each will help to determine the power and speed of a CPU.
(ii) Memory Unit (MU)
Memory is split into two types and they are Internal Memory and the External Memory
Internal Memory: Internal Memory is also known as primary memory. RAM and ROM are examples.
RAM stands for Random Access Memory. RAM is Computer's short-term Memory. RAM is a volatilememory which stores information only as long as the computer has power. Once the computer is shut down, the information stored in RAM is lost. Thus, the information in RAM needs to be saved to a storage device before the computer is turned off.
ROM stands for Read Only Memory. The instructions in ROM are also called firm-ware. The instructions in ROM are non-volatile. They stay in ROM even when the computer is turned off therefore it is called the permanent memory.
Cache is another type of computer memory that makes the CPU process data or instructions faster. Cache is a high speed, high performance memory to which read and write operations can be done faster than RAM.
External Memory: External Memory allows the permanent storage of large quantities of data. External memory can be Secondary or tertiary.
Secondary Storage Devices are used to store information that needs to be used again and again. Hard disks, USB, Flash Drives, CDs, DVDs, Memory Card, Solid State Disk (SSD) are some secondary storage devices.
Tertiary Storage Device is used to store information that is needed occasionally for review purposes or for restoring information after a system failure. It includes magnetic tape, network server or high capacity optical disc.
Memory of a Computer
Memory is usually measured in bytes. The smallest measurement of memory is bit.
■ 8 bits = 1 byte.
■ 1 Kilobyte (KB) = 1,024 Bytes
■ 1 Megabyte (MB) = 1,024 Kilobytes
■ 1 Gigabyte (GB) = 1024 Megabytes
■ 1 Terabyte (TB) = 1024 Gigabytes
■ 1024 terabytes = 1 Petabyte (PB)
(iii) Input/Output
Computer peripherals include all the additional hardware components grouped around the CPU and memory. These are the Input/output (I/O) units and storage devices such as hard disk, VDU (Video Display Unit), Key board, Mouse etc.
There has to be a physical channel that permits users to supply information to the computer. Devices that allow users to supply data to the computer are termed as 'input' devices. Input unit enables us to enter data into a computer. The common input devices are Keyboard and Mouse.
Similarly, here would be a physical channel that permits a computer to convey the processed information to the outside world. They are called 'output' devices. Some of the output devices are Monitor, Printer and Speakers.
Input and output devices are indispensable, but are not a part of the CPU. They are also called peripheral devices, suggesting that they lie on the periphery of the CPU.
Some Input Devices
Optical Character Reader (OCR): An optical character reader is used to read characters of a special type font printed on conventional paper with conventional ink. A logical system then determines the character from the pattern analysed. Only a limited number of characters in a given font can be recognised.
Magnetic Ink Character Reader (MICR) :Banks use another input device called a Magnetic Ink Character Reader. MICR is a character recognition technology; for characters printed on documents (such as cheques) using a special magnetic ink. A magnetic ink character reader is used to find such characters.
Optical Mark Reader (OMR): Here, special pre printed forms designed with boxes. Each box is explained distinctly so that user clearly understands what response he is marking. Such a document is read by an optical mark reader (OMR) which translates the marks into electrical pulses which are fed to the computer. Such documents are mostly used in areas where responses are one out of a few alternatives and the volume of data to be processed is large.
Barcode Reader: Here, small bars of varying thickness and spacing are printed on packages, tags, etc., that are read by the optical reader and converted into electrical pulses. The bar code is read by a hand - held optical device which illuminates the barcode, the reflected light is sensed by the sensor and converted to bits and inputs to a computer's memory. This device is commercially used in retail stores and book shops.
Magnetic disc and tape: Magnetic disc can record data as output from main memory (such as results of computations) or can serve as input devices, returning data to main memory.