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Central Processing Unit Part 2



The Two Types Of RAM

=> Static RAM (SRAM) – It retains stored information till computer is under working.
=> Dynamic RAM (DRAM) – It loses its stored information in a very short span of time even though computer is under working.

ROM – It is permanent memory storage as the name suggests, is that part of the memory which only ‘Read’ by the computer. ROM is non-volatile memory which has fixed instructions on it.
When the system is turn on the ROM instructions are instantly activate to get all input / output devices activated.

PROM – Programmable Read Only Memory – Is non-volatile type and instructions can be written once by the programmer and then can be sequently read. PROM chips are custom made for the user by the manufacturer.

EPROM – Erasable Programmable Read Only Memory is non-volatile type and which this type of memory instructions can be rewrite by the programmer using special techniques.
With the aid of special device that uses ultraviolet light, the data on an EPROM chip can be erased and new data can be recorded on it place.

EEPROM – Electronic Erasable Programmable Read Only Memory is an advance addition to the ROM family of chips to avoid the inconvenience of changing the instructions by taking the chip of the machine, instead this changes can be done electrically under software control. These chips are used in Point-of-Sale (POS) terminals.

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External Memory (Secondary Memory)

External memory is for the long term storage of information. Data from external memory will be transferred to the main memory before the CPU can operate on it. External memory allows the permanent storage of large quantities of data.

Examples of External Memory Are
=> Magnetic Tape
=> Magnetic Disk (Floppy Disk, Hard Disk and more)
=> Magnetic Drum
=> Magnetic Ink Character Reader (MICK)
=> Compact Disk Read Only Memory (CD-ROMS)

The Control Unit

It controls the fetching of instructions from the main memory and the subsequent execution of these instructions. Among other tasks carried out are the control of input and output devices and the passing of data to the Arithmetic/Logical Unit for computation.

The Arithmetic/Logical Unit (ALU)

An arithmetic-logic unit (ALU) is the part of a computer processor (CPU) that carries out arithmetic and logic operations on the operands in computer instruction words. The ALU is divided into two units in some processors, (1) an arithmetic unit (AU) and (2) a logic unit (LU). 

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