Page 54 - IT_Play_V1.0 Class9
P. 54
Memory Unit (MU)
Memory Unit or main storage stores the data, instructions, intermediate results and final results that are
ready for the output. All instructions or data are stored in the memory unit before being used by the
ALU or the CU. The main storage is divided into a number of storage locations that can be accessed by a
unique number or address known as the memory address. Within the CPU there are high-speed, special-
purpose memory units called registers. The Control Unit and the internal storage are linked together by sets
of parallel electrical conducting lines called buses. The buses that carry data are called ‘Data Buses’. To retrieve
data from the memory, it is necessary to identify the address of data in the main memory. The address is
identified by ‘Address Buses’. The buses that carry control signals are called ‘Control Buses’.
Computer Memory
Computer memory refers to the location of storage of information. The CPU stores the data in the memory/
storage device that can be used or retrieved whenever required. Memory receives instructions and data from
the input devices and stores them till they are needed by other parts of the computer. Once the instructions
are executed, the results are transferred to a permanent location which are then stored in a storage device.
Memory can be classified into two types: Primary Memory and Secondary Memory.
Memory Storage Units
A computer understands its own language. All the data and information that are fed into a computer are
converted into its own (machine) language. Its language consists of two digits i.e, 0 and 1 which are called
Binary Digits. Each digit i.e., 0 or 1 is known as a bit. A group of four bits is called a Nibble. A group of eight
bits is called a Byte. Conventionally, byte is also known as the word length of a computer. Storage of data is
measured in multiples of bytes. Different units of storage of data are:
No. of Bits/Bytes Unit
8 bits 1 Byte
1024 Bytes 1 KiloByte
1024 KiloBytes (KB) 1 MegaByte
1024 MegaBytes (MB) 1 GigaByte
1024 GigaBytes (GB) 1 TeraByte
1024 TeraBytes (TB) 1 PetaByte
Primary Memory
Primary Memory is also known as Main Memory. It is that part of the CPU which stores the data and
instructions that are meant for current processing or for the internal management of the computer. It has a
limited capacity for the storage of data. Primary Memory can be classified into two groups:
RAM (Random Access Memory) ROM (Read-only Memory)
RAM
It holds the information temporarily, during the ongoing operation of a computer. When
a computer is under operation, the data or instructions are stored in its memory for
instant access. During the course of the execution of instructions, some intermediate
results may be produced which are stored in the RAM.
52 Information Technology Play (Ver 1.0)-IX

