COMPUTER SYSTEM (CLASS - XI) (PART - 3)

COMPUTER SYSTEM

Units of computer Memory

S. No.	Unit	Short Name	Full Name
1	1 Bit	Bit	Binary Digit
2	8 Bits	1 Byte	Byte
3	210 i.e. 1024 Bytes	1 KB	Kilo Byte
4	210 i.e. 1024 KB	1 MB	Mega Byte
5	210 i.e. 1024 MB	1 GB	Giga Byte
6	210 i.e. 1024 GB	1 TB	Terra Byte
7	210 i.e. 1024 TB	1 PB	Peta Byte
8	210 i.e. 1024 PB	1 EB	Exa Byte
9	210 i.e. 1024 EB	1 ZB	Zetta Byte

Memory Access Time: The amount of time taken to produce data required from memory, from the start of access until the availability of data, is called Memory Access Time.

Parts of Main Memory (Primary Memory):

The main memory divided into two parts:

RAM (Random Access Memory)
ROM (Read Only Memory)

Random Access Memory: It is the memory cells that can be accessed for information transfer from any desired random location. That is, the process of locating a word in memory is the same and requires an equal amount of memory, thus the name “random access”.

The main drawback of RAM memory is that it is a volatile memory. That is, when the power goes off, the contents of RAM get erased.

Types of RAM

The RAM chips in a computer can be of two types:

Dynamic RAM (DRAM)

Static RAM (SRAM)

Dynamic RAM (DRAM): Dynamic RAM consists of a transistor and capacitor that’s capable of storing an electric charge. Depending on the switching action of the transistor, the capacitor either contains no charge (0 bit) or does hold a charge (1 bit). The dynamic RAM provides volatile storage i.e. contents are lost in the event of power failure.

Static RAM (SRAM): SRAM is also volatile but as they are supplied with power, they need no special regenerator circuits to retain the stored data. The static RAM consists eventually of internal flip-flop that store the binary information. The stored information remains valid as long as power is applied to the unit.

Note: A flip-flop is a binary cell capable of storing one bit of information.

Read Only Memory (ROM):  ROM refers to read only memory where only read operation can take place. The ROM is a non-volatile memory. Both RAM and ROM are parts of primary memory.

There are various types of ROM which are given below:

1.      Programmable Read Only Memory (PROM)

2.      Erasable Programmable Read Only Memory (EPROM)

3.      Electrically Erasable Programmable Read Only Memory (EEPROM)