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 groups of bits is called words.

The information stored in memory has a sequence of 0’s and 1’s. A group of eight bits (0s and/or 1s) is called a 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 a computer, or we can say that data transfer/movement from memory to the outside environment is done by the read and write operations.

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 an internal decoder. This number is called the 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 a random manner. Address lines are used to select the location in memory, whereas data is transferred through data on occuring a control signal occurs through control lines.

Random-access memory can perform read and write operations, with a proper control signal. Read-only memory (ROM), as the name indicates, is a memory unit that performs the read operation only. Such a type of memory does not have a write capability. It means that 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 a memory read operation. It means the read operation specifies a transfer out operation. The steps that must be taken for transferring stored data out of memory are as follows:

1. Provide the address of the 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 the address lines and provide that information to the data lines. However, the contents of the specified memory word do not change after the read operation.

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

This read operation can be written as follows:

Read: DR ← M[AR]

In the above expression, Read is the 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 the 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 the write operation, the internal circuits inside the memory provide the desired function. The steps that must be taken for transferring new data to be stored in memory are as follows:

1. Provide the address of the 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 in memory, the previous information will be overwritten and lost after the writing operation.

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

Write: M[AR] ← DR

In the above expression, Write is a control input, and the 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. The figure below shows the basic write operation in computer memory.

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

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