Primary Memory or Main Memory - Computer Education

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Tuesday, September 11, 2018

Primary Memory or Main Memory

Primary Memory or Main Memory :- The memory unit that communicates directly with the CPU is called the main memory. This is the Computer's working storage. It is one of the most important part of the computer as it determines the size and number of programs that can be simultaneously held within the computer. So we can say that the speed of a computer depends on the primary memory. The documents on which we are working on is stored in primary memory or main memory. Computer main memory comes in two principal varieties - Random Access Memory (RAM) and Read-Only Memory (ROM)


Random Access Memory (RAM) :- RAM is a read/write memory. It is a volatile memory. It retains the stored information as long as it is supplied with power. The contents of RAM is erased when the power to the computer is turned off. RAM can be read and written to anytime the CPU commands it. Random Access Memory is used for program execution and short term data storage, so the computer does not have to take the time to access the hard drive to find the files it requires. More RAM will normally contribute to a faster PC.

In random access memory the memory cells can be accessed for information transfer from any desired random location. The communication between a memory and its environment is made by data input and output lines, address lines and control lines that specify the direction of transfer.

The data input lines provide the information to be stored in memory and the data output lines supply the information coming out of memory. The address lines provide a binary number that specify a particular cell chosen among the cells in the memory. The two control inputs specify the direction of transfer the desired word.

The two operations that a random access memory can perform are the write and read operations. The write signal specifies a transfer-in operation and the read signal specifies a transfer-out operation.

The steps that must be taken for the purpose of transferring a new word to be stored into memory are as follows:-

1) Apply the binary address of the desired word into the address lines.
2) Apply the data bits that must be stored in memory through the data input lines.
3) Activate the write input.

The memory untill will then take the bits presently available in the input data lines and stored them in the cell specified by the address line.

The steps that must be taken for the purpose of transferring a stored word out of memory are as follows:-

1) Apply the binary address of the desired word into the address lines.
2) Activate the read input.

The memory unit will then take the bits from the cell that has been selected by the address and apply them into the data output lines. The content of the selected cell does not change after reading.

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