Central Processing Unit

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Shree Bhawani Niketan Institute of Technology & Management, Jaipur

CPU
(Central Processing Unit)

Submitted to-
Mr. Manish Gupta By- Amir Khan
Date- April 12, 2013

Definition-
central processor unit, is the hardware within a computer that carries out the instructions of a computer program by performing the basic arithmetical, logical, and input/output operations of the system

Introduction to CPU-
* Central processing unit etched on silicon chip called microprocessor * Contain tens of millions of tiny transistors

Components of the CPU-

* Control unit
* Moves data and instructions between main memory and registers * Arithmetic logic unit (ALU)
* Performs computation and comparison operations
* Set of registers
* Storage locations that hold inputs and outputs for the ALU
Control Unit
The control unit coordinates the components of a computer system. It fetches the code of all of the instructions in the program. It directs the operation of the other units by providing timing and control signals. All computer resources are managed by the CU. It directs the flow of data between the Central Processing Unit (CPU) and the other devices.

The control unit is the circuitry that controls the flow of data through the processor, and coordinates the activities of the other units within it. In a way, it is the "brain within the brain", as it controls what happens inside the processor, which in turn controls the rest of the computer. The examples of devices that require a control unit are CPUs and graphics processing units (GPUs). The modern information age would not be possible without complex control unit designs.

Arithmetic logic unit (ALU)
In computing, an arithmetic and logic unit (ALU) is a digital circuit that performs integer arithmetic and logical operations. The ALU is a fundamental building block of the central processing unit of a computer, and even the simplest microprocessors contain one for purposes such as maintaining timers.

schematic symbol

Registers

In computer architecture, a processor register is a small amount of storage available as part of a CPU or other digital processor. Such registers are (typically) addressed by mechanisms other than main memory and can be accessed more quickly. Almost all computers, load-store architecture or not, load data from a larger memory into registers where it is used for arithmetic, manipulated, or tested, by some machine instruction.

Categories of registers-
* 8-bit register
* 32-bit register

A processor often contains several kinds of registers, that can be classified accordingly to their content or instructions that operate on them: * User-accessible registers The most common division of user-accessible registers is into data registers and address registers. * Data registers can hold numeric values such as integer and floating-point values, as well as characters, small bit arrays and other data * Address registers hold addresses and are used by instructions that indirectly access primary memory. * Conditional registers hold truth values often used to determine whether some instruction should or should not be executed. * General purpose registers (GPRs) can store both data and addresses, i.e., they are combined Data/Address registers. * General purpose registers (GPRs) can store both data and addresses, i.e., they are combined Data/Address registers.

Actions Performed by CPU
Fetch cycle| CPU: * Fetches an instruction from primary storage * Increments a pointer to location of next instruction * Separates instruction into components (instruction code and data inputs) * Stores each component in a separate register| Execution cycle| ALU: * Retrieves instruction code from a register * Retrieves data inputs from registers * Passes data inputs through internal circuits to...
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