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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.




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