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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.

                 RAM is a volatile memory i.e., when a computer is switched ‘OFF’ or the power
                 supply is interrupted, all the stored information in it disappears. RAM chip is
                 made of Metal Oxide Semiconductor (MOS). RAM is available in the form of chip

                 a of different capacities, For example, 4 GB, 8 GB, 16 GB, 32 GB, 64 GB, etc. You can upgrade the capacity of
                 existing RAM in a computer by installing extra RAM chips in addition to the existing ones. There are different
                 types of RAM like SRAM, DRAM, SDRAM, EDRAM, ECRAM, etc.

                 ROM

                 It stores a set of predefined instructions for the internal operations of a computer.
                 It is also referred to as  non-volatile  memory or  firmware .

                 Once the user switches ‘ON’ the computer, the computer automatically does a
                 series of sequential tasks like POST (Power On Self Test), RAM Test, etc. before
                 the user starts its operation. The instructions for such a predefined set of tasks
                 are stored in the ROM. Such information on this memory can only be read.
                 There are different types of ROM like PROM, EPROM, EEPROM, Flash ROM, etc.

                 BIOS (Basic Input/Output System) is stored in ROM and it operates when the computer is switched ‘ON’. It
                 contains a set of essential software that test the setup of hardware devices during startup. It helps to start the
                 operating system and supports the transfer of data among the hardware devices.
                 Cache Memory
                 Besides RAM and ROM, there are some other primary memories like the Cache or Buffer memory. Cache
                 Memory is a part of the CPU and is used when there is a swapping of information between the primary
                 memory and the ALU.

                 Units of Storage

                 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.



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