1. COMPUTER SYSTEM FUNDAMENTAL Copyright @ Genetic Computer School 2008 2-1 THE PROCESSING UNIT LESSON 2

2. COMPUTER SYSTEM FUNDAMENTAL Copyright @ Genetic Computer School 2008 2-2 LESSON OVERVIEW  WHAT IS A CENTRAL PROCESSING UNIT?  MAIN COMPONENTS AND STRUCTURE OF THE CPU  HOW THE CPU WORKS  DEFINITION OF A MICROPROCESSOR

3. COMPUTER SYSTEM FUNDAMENTAL Copyright @ Genetic Computer School 2008 2-3 CENTRAL PROCESSING UNIT It is the "brain" of the computer it reads and executes program instructions, performs calculations, and makes decisions. It is responsible for storing and retrieving information on disks and other media. It also handles information on from one part of the computer to another like a central switching station that directs the flow of traffic throughout the computer system. It is the essential component of a computer because it is the part that executes the programs and controls the operation of all the hardware. The CPU resides inside a box known as the system unit, along with various support devices and tools for storing information.

4. COMPUTER SYSTEM FUNDAMENTAL Copyright @ Genetic Computer School 2008 2-4 CENTRAL PROCESSING UNIT Powerful computers may have several processors handling different tasks, although there will need to be one central processing unit controlling the flow of instructions and data through the subsidiary processors.

5. COMPUTER SYSTEM FUNDAMENTAL Copyright @ Genetic Computer School 2008 2-5 MAIN COMPONENTS OF THE CPU

6. COMPUTER SYSTEM FUNDAMENTAL Copyright @ Genetic Computer School 2008 2-6 CONTROL UNIT The control unit must communicate with both the arithmetic/logic unit and memory. The functions performed by the control unit vary greatly by the internal architecture of the CPU, since the control unit really implements this architecture. The control unit performs the tasks of fetching, decoding, managing execution and then storing results. The control unit uses the instruction contained in the Instruction Register to decide which circuits need to be activated. It co- ordinates the activities of the other two units as well as all peripheral and auxiliary storage devices linked to the computer. The control unit instructs the arithmetic logic unit which arithmetic operations or logical operation is to be performed. It is literally in control.

7. COMPUTER SYSTEM FUNDAMENTAL Copyright @ Genetic Computer School 2008 2-7 MEMORY UNIT The Memory Unit is the part of the computer that holds data and instructions for processing. Although it is closely associated with the CPU, in actual fact it is separate from it. Memory associated with the CPU is also called primary storage, primary memory, main storage, internal storage and main memory.

8. COMPUTER SYSTEM FUNDAMENTAL Copyright @ Genetic Computer School 2008 2-8 RAM,RANDOM ACCESS MEMORY It is really the main store. It is the place where the programs and software we load gets stored When the Central Processing Unit runs a program, it fetches the program instructions from the RAM and carries them out. If the Central Processing Unit needs to store the results of calculations it can store them in RAM. Random Access Memory can have instructions read from it by the CPU and also it can have numbers or other computer data written to it by the CPU. The more RAM in your computer, the larger the programs you can run. When we switch a computer off, whatever is stored in the RAM gets erased.

9. COMPUTER SYSTEM FUNDAMENTAL Copyright @ Genetic Computer School 2008 2-9 ROM, READ ONLY MEMORY ROM is "built-in" computer memory containing data that normally can only be read, not written to. ROM contains the programming that allows your computer to be "booted up" or regenerated each time you turn it on. The data in ROM is not lost when the computer power is turned off. The ROM is sustained by a small long-life battery in your computer. If you ever do the hardware setup procedure with your computer, you effectively will be writing to ROM.

10. COMPUTER SYSTEM FUNDAMENTAL Copyright @ Genetic Computer School 2008 2-10 Arithmetic Logic Unit The accumulator is used to accumulate results. It is the place where the answers from many operations are stored temporarily before being put out to the computer's memory. The other general- purpose registers hold data on which operations are to be performed by the arithmetic logic unit.

11. COMPUTER SYSTEM FUNDAMENTAL Copyright @ Genetic Computer School 2008 2-11 ARITHMETIC AND LOGIC UNIT The arithmetic logic unit executes arithmetic and logical operations. Arithmetic operations include addition, subtraction, multiplication and division. Logical operations compare numbers, letters and special characters.

12. COMPUTER SYSTEM FUNDAMENTAL Copyright @ Genetic Computer School 2008 2-12 Comparison operations Comparison operations test for three conditions:  Equal-to condition  Less-than condition  Greater-than condition Relational operations (=, ) are used to describe the comparison operations used by the arithmetic logic unit.

13. COMPUTER SYSTEM FUNDAMENTAL Copyright @ Genetic Computer School 2008 2-13 LOGIC FUNCTIONS The arithmetic logic unit performs logic functions such as AND, OR and NOT.

14. COMPUTER SYSTEM FUNDAMENTAL Copyright @ Genetic Computer School 2008 2-14 STEPS, CPU PERFORMS WHEN EXECUTING AN INSTRUCTION 1.The control unit gets the instruction from memory. 2.The control unit decides what the instruction means and directs the necessary data to be moved from the memory to the arithmetic logic unit. 3.The arithmetic logic unit performs the actual operation on the data. 4.The result of the operation is stored in memory or a register MACHINE CYCLE THE INSTRUCTION TIMETHE EXECUTION TIME

15. COMPUTER SYSTEM FUNDAMENTAL Copyright @ Genetic Computer School 2008 2-15 HOW CPU WORKS?

16. COMPUTER SYSTEM FUNDAMENTAL Copyright @ Genetic Computer School 2008 2-16 DEFINITION: MICROPROCESSOR In a microcomputer, the CPU is contained on a single silicon chip called the microprocessor. A microprocessor is a computer processor on a microchip. It's sometimes called a logic chip. It is the "engine" that goes into motion when you turn your computer on. A microprocessor is designed to perform arithmetic and logic operations that make use of small number-holding areas called registers. Typical microprocessor operations include adding, subtracting, comparing two numbers, and fetching numbers from one area to another. When the computer is turned on, the microprocessor is designed to get the first instruction from the Basic Input/Output System (BIOS) that comes with the computer as part of its memory.