Machine Cycle

Definition of Machine cycle


A machine cycle, also called a processor cycle or a instruction cycle, is the basic operation performed by a central processing unit (CPU). A CPU is the main logic unit of a computer.

 A machine cycle consists of a sequence of three steps that is performed continuously and at a rate of millions per second while a computer is in operation. They are fetch, decode and execute. There also is a fourth step, store, in which input and output from the other three phases is stored in memory for later use; however, no actual processing is performed during this step.



Fetch step
In the fetch step, the control unit requests that main memory provide it with the instruction that is stored at the address (i.e., location in memory) indicated by the control unit's program counter.

The control unit is a part of the CPU that also decodes the instruction in the instruction register. A register is a very small amount of very fast memory that is built into the CPU in order to speed up its operations by providing quick access to commonly used values; instruction registers are registers that hold the instruction being executed by the CPU. Decoding the instructions in the instruction register involves breaking the operand field into its components based on the instructions opcode.

Opcode (an abbreviation of operation code) is the portion of a machine language instruction that specifies what operation is to be performed by the CPU. Machine language, also called machine code, refers to instructions coded in patterns of bits (i.e., zeros and ones) that are directly readable and executable by a CPU.

A program counter, also called the instruction pointer in some computers, is a register that indicates where the computer is in its instruction sequence. It holds either the address of the instruction currently being executed or the address of the next instruction to be executed, depending on the details of the particular computer. The program counter is automatically incremented for each machine cycle so that instructions are normally retrieved sequentially from memory.


The control unit places these instructions into its instruction register and then increments the program counter so that it contains the address of the next instruction stored in memory. It then executes the instruction by activating the appropriate circuitry to perform the requested task. As soon as the instruction has been executed, it restarts the machine cycle, beginning with the fetch step.

Comments

Post a Comment

Popular posts from this blog

Reading and Writing Operation of SRAM

Image
The diagram below is illustrate Static Random Access Memory (SRAM)Cell for the explanation. SRAM cell is make up of 2 inverters are cross-connected to form a latch .The latch is connected to 2 bit line by transistor T1 and T2 . T1 and T2 can switch opened or closed under control of word line.When word line is ground level, the transistors are turned off and the latch retrains its state. During the Read Operation ,Word line is activated to close switches T1 and T2 . If the cell is in state 1; the signal on b line is high and the signal on b’ line is low.The opposite is true if the cell is in state 0.Thus, b and b’ are always complements of each other’s. The sense /write circuit at the end of the two bit line monitors their state and sets the corresponding output accordingly. While in Write Operation ,the Sense/Write circuit drives bit lines b and b’, instead of sensing their state.It places the appropriate value on bit line b and its complement on b’ and activate the word ...
Read more

Reading & Writing Operation of DRAM

Image
In Dynamic Random Access Memory CELL , transistor acts as a switch to Close (allowing current to flow) when voltage applied in address line or Open (no current flow) when no voltage applied in address line.Address Line also known as word line .Which use to signal the transistor to close or open. During the Write operation ,a voltage is applied on the bit line and a signal applied to the address line to close the transistor.Then the voltage applied on the bit line will transfer to capacitor and store in the capacitor However the capacitor has tendency to discharge and has to refresh to maintain the bit. While in Reading Operation ,the instruction find the bit store using the address line to read the data or bit. When the address line is selected ,the transistor turns on and the charge stored on the capacitor is fled out onto a bit line and to sense amplifier. Sense amplifiers compare the capacitor voltage to reference value to determine the logic 1 or logic 0.The read out from ...
Read more

Method to Convert from Stream to Json C#

Recently I was using the C# HttpClient to make REST request but I found that is was quite troublesome so I have changed to using HttpWebRequest instead. So want the HttpWebRequest result is return it was in Stream form. I not able to convert it into Json. this is the method i convert the stream to JSON. HttpWebResponse response = ( HttpWebResponse ) requirejs . GetResponse (); Stream stream = response . GetResponseStream (); StreamReader sr = new StreamReader ( stream ); var serializer = new System . Web . Script . Serialization . JavaScriptSerializer (); var jsonObject = serializer . DeserializeObject ( sr . ReadToEnd ()); As you can see that jsonObject is an object. Now you can parse it into the Json(JsonObject); If you have any question can leave a comment below.
Read more