Microprocessor

Microprocessor

A microprocessor is an electronic circuit that is fabricated on a single chip. It is the heart of all the computers. The instructions given in a program are interpreted and carried out by the processing unit of computer. So, we can say that a microprocessor is a multipurpose, programmable device that reads binary instructions from a storage device called memory, accepts binary data from input units and processes data according to these instructions and provide results as output. A processor is also known as CPU which is also called as brain of the computer.

The main components of CPU are:

1.     Control Unit

2.     Arithmetic Logic Unit

3.     Registers

1.   Control Unit(CU) -> A control unit is that part of computer, which makes the ALU and memory work in synchronization with the data. It is responsible for carrying out all the instructions stored in the program. It decodes the fetched instruction, interprets (understands) it and sends control signals to input/output devices until the required operation is done properly by ALU and memory.

Control Unit performs two basic functions:

1.     It fetches the instruction and determines the operation required for its execution.

2.     It enables the CPU to execute the various operations required for the execution of the instruction in a proper sequence.

2.    Arithmetic Logic Unit (ALU) -> It is one of main components of the CPU. This is where all arithmetic & logic operations are done. Arithmetic calculations include addition, subtraction, multiplication and division. Logical decisions involve comparison of two data items to see which one is larger or smaller or equal.

3.   Register -> A register is a group of flip-flops. The flip-flop is nothing but an electronic circuit capable of storing one bit (either 0 or 1) at a given time. These memory elements are capable of receiving information, holding it and transferring it very quickly. The processor registers are required for manipulating data and a register for holding memory address. Registers can be of different sizes; 8-bit, 16-bit, 32-bit etc. Some of the commonly used registers are:

1.     Data Register(DR): It holds the operands read from memory.

2.     Memory Address Register(MAR): It holds a memory address during a computer run.

3.     Accumulator(AC): It is the main register in ALU. It contains one of the operands of an operation to be performed in ALU. The other operand is in temporary register. The result of the operation is accumulated in this register.

4.     Instruction Register(IR): It is a part of the control unit. The instruction read from the memory is placed in IR.

5.     Temporary Register(TR): It is used for holding temporary data.

6.     Program Counter(PC): PC keeps the track of  the memory address of next instruction to be fetched and executed.

7.     Input Register(INPR): It stores the input character received from input device.

8.     Output Register(OUTR): It holds the character from an output device.

9.     Clock: It is a device that generates electronic pulses to synchronise all the operations taking place in the computer.

  Buses

A collection of wires through which data is transmitted from one part of a computer to another. You can think of a bus as a highway on which data travels within a computer. When used in reference to personal computers, the term bus usually refers to internal bus. This is a bus that connects all the internal computer components to the CPU and main memory. The size of a bus, known as its width, is important because it determines how much data can be transmitted at one time. For example, a 16-bit bus can transmit 16 bits of data, whereas a 32-bit bus can transmit 32 bits.

Buses are classified into three types:

1.     Data Bus: It is a bidirectional group of lines on which data can flow both ways i.e. from microprocessor to device and from device to microprocessor. The number of lines in a data bus are generally in proportion to the processing power of microprocessor.

2.     Address Bus: It is a unidirectional group of lines on which address of a device or memory location is sent by the microprocessor. The width of the address bus equals to the number of bits in the Memory Address Register(MAR). When the microprocessor wants to read data or instruction from memory location it sends the address of location on the address bus.

3.     Control Bus: It carries the control signals between the units of computer. For example, if the processor has to send READ and WRITE commands to memory, START command to I/O units etc such signals are carried by control bus.

 Clock Speed

The speed at which a microprocessor executes instructions is known as clock speed. Every computer contains an internal clock that regulates the rate at which instructions are executed and synchronizes all the various computer components. The CPU requires a fixed number of clock ticks (or clock cycles) to execute each instruction. The faster the clock, the more instructions the CPU can execute per second. The speed with which an instruction is executed is directly related to the computer’s built in clock speed, which is number of pulses produced per second. This clock speed is measured in Megahertz(MHz), where mega means million and hertz mean cycle per second. Now a day’s microprocessors have a speed of several GHz.