The instruction execution cycle performs the following steps:

a. Instruction Cycle:

1. Instruction Fetch
2. Instruction Decode

1. Instruction Fetch:
The first step is to fetch the instruction to be executed. This is called Instruction Fetch operation. Execution of the program starts from the Program Counter Register (PC) which has the first instruction of the program. The contents of the PC are then transferred to the Memory Address Register (MAR) and a READ signal is sent to the memory and is read out and loaded into the Memory Data Register (MDR). Later, the contents of the MDR are transferred to the Instruction Register (IR).

2. Instruction Decode:
In the instruction Decode operation, the Instruction Register (IR) determines the type of instruction and selects signals accordingly. It separates the operation part of instruction and is sent to the control unit and the address part is sent to MAR of the instruction.

b. In Execution cycle:
The decoded instruction is executed finally. Instruction Decoder generates microinstructions and the timing signals that control the various processing elements involved in executing the instruction.