Memory Operations

Memory Operations

• We know that both program instructions and data operands are stored in the memory. To execute an instruction processor has to fetch instruction and read the operand or operands if necessary from the memory. After execution of instruction processor may store the result or modified operand back in the memory. Thus, there are two basic operations required in the memory access: 1. Load (Read or fetch) 2. Store (write).

• Load operation: In the load operation the contents of the specified memory location are read by the processor. For load operation processor sends the address of the memory location whose contents are to be read and generates the appropriate read signal to indicate that it is a read operation. The memory identifies the addressed memory location and sends the contents of that memory location to the processor. This operation is illustrated in Fig. 6.8.1 (a).

• Store operation: In the store operation the data from the processor is stored in the specified memory location. For store operation processor sends the address of the memory location where the data is to be written on the address lines, the data

to be written on the data lines and generates the appropriate write signal to indicate the store operation. The memory identifies the addressed memory location and writes the data sent by the processor at that location destroying the former contents of that location. This operation is illustrated in Fig. 6.8.1 (b).

• The data items or instructions which are transferred between memory and processor may be either byte or word. They can be transferred using a single operation. Mainly this transfer takes place between processor registers and the memory locations.

• We know that processor has small number of built-in registers. Each register is capable of holding a word data. These registers are either the source or the destination of a transfer to or from the memory.

Review Question

1. Explain the data transfer operations between memory and the processor.