Characteristics and Classification of Machine Cycle

Asked By 200 points N/A Posted on -

Hello everyone,

I have some question regarding Machine Cycle. About the machine cycle all I know is a machine cycle is the time it takes a microprocessor to fetch and execute a complete instruction or not. Is it true? Please define Machine Cycle. What are the characteristics of machine cycle and classification of the machine cycle. It will be really helpful.

Thanks in advance.

Best Answer by Austain
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Answered By 10 points N/A #94279

Characteristics and Classification of Machine Cycle



  • The question you’re asking is an interesting question. And I’m really happy that it my privilege to give the answer of this question. As you asked –
  • Question: Weather a machine cycle is the time it takes a microprocessor to fetch and execute a complete instruction or not.
  • The Answer is true.
  • I can see that you have knowledge about a machine cycle. Here I’m going to share some of my ideas about Machine cycle. Hope you’ll find it effective.
  • A machine cycle.
  • A machine cycle, also called a processor cycle or an instruction cycle, is the basic operation performed by a central processing unit (CPU). It can also be said that the time required to complete the one operation. As the CPU is the main logic unit of a computer.

Characteristics of machine cycle:

  • Consists of a sequence of four performed continuously.
  • Works at a rate of millions per second.
  • Fetches, decodes and executes.
  • Stores input and output from the other source.


  • A machine cycle can be divided into two smaller cycles.
  • Instruction cycle and
  • Execution cycle.

Instruction cycle: In instruction cycle CPU takes two steps –

  • Fetching: Before the CPU can execute an instruction, the control unit requests the main memory to provide it with the instruction that is stored at the address memory indicated by the control unit's program counter.
  • Decoding: The control unit is a part of the CPU that also decodes the instruction in the instruction register. Decoding the instructions in the instruction register involves breaking the operand field into its components based on the instructions.
  • A register is a very small amount of very fast memory that is built into the CPU.

Execution cycle: In execution cycle CPU also takes two steps –


  • In the process of executing, the CPU carries out the instructions in order to convert them into microcode or operation code.
  • The operation code is the portion of a machine language instruction that specifies what operation is to be performed by the CPU.


  • The control unit places these instructions into its instruction register and then increments the program counter. Then the CPU stores the result of an instruction in memory.
  • As soon as the instruction has been executed the machine cycle again starts beginning with the fetch step.

Hope you got some idea about Machine Cycle.


Answered By 0 points N/A #94281

Characteristics and Classification of Machine Cycle



Yes. Machine cycle, also known as "processor cycle" and "instruction cycle", is the completion of the series of 4 steps (basic operation) that a CPU executes for each machine language instruction. This is carried out continuously with a rate of millions per second by the CPU (Central Processing Unit). 

These 4 steps are:

1. Fetch 2. Decode 3. Execute 4. Store.

  • Step 1 (Fetch) refers to the reading of the machine language instruction.
  • Step 2 (Decode) refers to interpreting the read machine language instruction into a code.
  • Step 3 (Execute) refers to the execution of the code.
  • Step 4 (Store) refers to the storing of the code in the memory.
  • Machine cycles are classified as "Status signals" and "Control signals".
  • For an 8085 microprocessor, the available types of machine cycle are Opcode fetching, Memory Read, Memory writes, I/O Read, I/O Write, INTR Acknowledge, and Bus Idle.

Hope this helps you.

Answered By 590495 points N/A #325905

Characteristics and Classification of Machine Cycle


The other term for “machine cycle” is “processor cycle” or “instruction cycle”. This is the basic operation performed by a CPU or Central Processing Unit. Machine cycle is composed of a series of three steps performed continuously at a rate of millions per second while a computer is in operation. These three steps are fetch, decode, and execute.

There is also a fourth step called “store” wherein input and output from the other three phases is stored in the memory for later use but there is no actual processing performed in this step. In the fetch step, the control unit requests instructions from the main memory stored at a memory’s location indicated by the program counter or the instruction counter.

In the decode step, received instructions are decoded in the instruction register which includes breaking the operand field down to its components based on the instruction’s opcode or operation code. In the execute step, this includes the instruction’s opcode because it specifies the required CPU operation. The program counter indicates the instruction sequence for the computer.

These instructions are arranged into the instructions register and as every instruction is executed, the program counter is incremented so that the next instruction is stored in the memory. The right circuitry is then activated to perform the requested task. As soon as the instructions have been executed, it restarts the machine cycle which begins the fetch step.

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