Difference Between Machine Cycle and Instruction Cycle

Primary Difference

Digital devices have to work in a different manner than human beings, while we input data into the computer from the external devices, it becomes necessary for the computer to understand all the instructions coming their way, this process is not that simple and involves many different kinds of activities before we reach a conclusion. The terms getting defined in this article are machine and instruction cycle, and most commonly considered the same name of a particular activity. They both have four main steps involved that help in decoding the data and making it acceptable for both the computers and the person using the device.

Comparison Chart

Machine CycleInstruction Cycle
DefinitionThe steps that get performed by the processor getting employed in a device and all the instructions that get implemented.A process by which a computer takes an instruction given by a program then understands it and executes it from memory.
ProcessesFetch, decode, execute and store.Fetch, decode, execute and run.
ComponentsMemory Unit and Central Processing UnitArithmetic Logic Unit, Registers, Data and Memory.
ValueThe Steps required by CPU to fetch and execute an Instruction is called an Instruction Cycle.The time Required by the microprocessor to complete the operation of accessing memory or I/O devices is called machine cycle.

Definition of Machine Cycle

A machine cycle defines itself as the step that gets performed by the processor getting employed in a device and all the instructions that get implemented. It is a combination of four different processes that go along before an instruction becomes valid. It gets known that the computer works differently than other devices and has to understand whatever data that gets thrown their way. There are four main steps involved in the complete cycle, and they are called fetch, decode, execute and store. The first step is collecting the instructions that are coming the device’s way and doing that a control unit is required; whatever data originates from the main memory to the control unit is based on the particular things mentioned. The next step is decoding that information. A human being inputs the things they require through keyboard but the computer works on the bits and bytes. All this information is then decoded correctly to make it comfortable for the device to understand. The third step is to execute the commands; all the data is now in the system; it then converts to the proper format that the machine understands now the controls performed. The last step is the store process after the action completes the final result and all the related activities then go to the memory unit where they get stored on the hard drive. Data get moved and deleted according to the user, and the whole process gets repeated. These four steps complete the cycle which becomes critical when the machine has to work in an efficient manner.

Definition of Instruction Cycle

An instruction cycle is a process by which a computer gets an instruction given by a program, then understands it and executes it from memory. It is a continuous process that starts from the time when the computer starts and carries on until the computer is powered off. It is the responsibility of this cycle to understand all the information and then take appropriate steps. In the simplest of systems, when the devices were not that advanced, each instruction was carried out on its own. For example, if a person has to copy one thing from a particular place to other, then while the processes continued, no other action was possible. But with the improvement in technology, now the instruction sets continue parallel to each other. For example, when someone has to move one object to a new folder, while the processes carry on, they can still delete another object or change the names of folders. Primary parts that become connected here are the program counter that keeps track of all the memories and addresses from where an action stated. Memory data register that holds the addresses of a block of memory from reading to writing. The memory address register that holds the fetched memory. An instruction register that contains a brief instruction that just executed recently and the arithmetic logic unit that performs the logical and mathematical operations. The steps involved are same as the process mentioned above where the instruction that got fetched from the memory cell, then it is decoded to make it understandable for the computer, reading the instruction and then executing it becomes the next part.

Differences in a Nutshell

  1. A machine cycle defines itself as the step that gets performed by the processor getting employed in a device and all the instructions that get implemented. An instruction cycle is a process by which a computer takes an instruction given by a program, then understands it and executes it from memory.
  2. There are four main steps involved in the memory cycle, and they are called fetch, decode, execute and store. There are four main stages involved in the instruction cycle, and they get called fetch, decode, execute and run.
  3. Several instruction cycles can continue at the same time on a computer whereas only one machine cycle will define the time taken by an instruction to complete from the beginning until the end.
  4. The Steps required by CPU to fetch and execute an Instruction is called an Instruction Cycle. The time Required by the microprocessor to complete the operation of accessing memory or I/O devices is called machine cycle.
  5. Both these terms usually get considered as synonyms for each other; instruction sequence is most commonly used in realistic environments whereas machine cycle often spoke by non-specialists.

Conclusion

People who do not have much information about the systems that become involved on how a device functions will benefit a great deal from this article as it lays out proper definitions, differences and a comparison chart of the machine cycle and instruction cycle. They both are connected tightly and therefore required a comprehensive analysis done here.

Harlon Moss

Harlon currently works as a quality moderator and content writer for Difference Wiki. He graduated from the University of California in 2010 with a degree in Computer Science. Follow him on Twitter @HarlonMoss

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