Memory Transfer in Computer Architecture

Memory Transfer in computer architecture – A memory unit is defined as a collection of storage cells together with associated circuits, needed to transfer information in and out of storage. The memory stores the information in group of bits is called words.

The information stored in memory has sequence of 0’s and 1’s. A group of eight bits (0s and/or 1s) is called byte. The capacity of memories in computers is usually stated as the total number of bytes that can be stored.

Memory Transfer

Memory transfer in computer or we can say that data transfer/movement from memory to outside environment is done by the read and write opeartions.

The internal structure of a memory unit is specified by the number of words it contains and the number of bits in each word. Each word in the memory unit is assigned an identification number using internal decoder. This number is called address of that word. The special input lines, called address lines, are used to select one particular word.

In general, a computer system uses two types of memories: Random Access Memory (RAM) and Read Only Memory (ROM). In RAM, any memory cell can be accessed in random manner. Address lines are used to select the location in memory whereas data is transferred through data on occuring a control signal through control lines.

A random access memory can perform read and write operations, with proper control signal. Read only memory (ROM), as the name indicates, is a memory unit that performs the read operation only. Such type of memory does not have a write capability. It means, once the information stored in ROM is permanent and can not be changed.

Memory Read (Data Movement from memory)

The data movement from memory to the outside environment is called memory read operation. It means, the read operation specifies a transfer out operation. The steps that must be taken for transferring a stored data out of memory are as follows:

1. Provide address of stored data into address lines
2. Activate the control signal: read for reading operation

The memory unit will then retrieve the bits from the word that has been selected by address lines and provide that information into the data lines. However the contents of specified memory word do not change after read operation.

Consider an example of a memory unit that receives the address of the word from address register (AR). When read control signal occurs, it transfers the data from memory unit to another register named data register (DR).

This read operation can be written as follows:

Read: DR ← M[AR]

In the above expression Read is control input. A memory word is symbolized by the letter M. This causes a transfer-out operation from memory word M selected by the address in AR into data register DR. below figure shows the basic read operation in computer memory.

Memory write (Data Movement to Memory)

The data movement from outside environment into memory is called memory write. It means that the memory write is a transfer-in operation. On occuring the control signal for write operation the internal circuits inside the memory provide the desired function. The steps that must be taken for transferring a new data to be store into memory are as follows:

1. Provide address of register to store data to address lines
2. Activate the control signal: write for writing operation

The memory unit will then receive the data bits presently available in the data lines and store them in the word that has been selected by the address lines. When new information is stored into memory, the previous information will be overwritten and lost after writing operation.

Consider an example of a memory unit that receives the address of the word from address register (AR). When control signal, write, occurs, it receives the data from the register named data register (DR) and store into memory unit. The write operation can be written as follows:

Write: M[AR] ← DR

In the above expression Write is a control input and memory word is symbolized by the letter M. This causes a transfer-in operation from the data register DR to the memory word M selected by the address in register AR. below figure shows the basic write operation in computer memory.

Here we have understand how memory transfer/ data movement is done in computer architecture using the read and write operations.

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