Addressing Data in Memory

The process through which the processor controls the execution of instructions is referred as the fetch-decode-execute cycle, or the execution cycle. It consists of three continuous steps:

• Fetching the instruction from memory
• Decoding or identifying the instruction
• Executing the instruction

The processor may access one or more bytes of memory at a time. Let us consider a hexadecimal number 0725H. This number will require two bytes of memory. The high-order byte or most significant byte is 07 and the low order byte is 25.

The processor stores data in reverse-byte sequence i.e., the low-order byte is stored in low memory address and high-order byte in high memory address. So if processor brings the value 0725H from register to memory, it will transfer 25 first to the lower memory address and 07 to the next memory address.

x: memory address

When the processor gets the numeric data from memory to register, it again reverses the bytes. There are two kinds of memory addresses:

• An absolute address - a direct reference of specific location.
• The segment address (or offset) - starting address of a memory segment with the offset value