CHAPTER (3) The Central Processing Unit (CPU) Emad Salem

The central processing unit (CPU)central processing unit (CPU) The central processing unit (CPU) is a complex set of electronic circuitry that executes program instructions; it consists of a control unit and an arithmetic/logic unit.central processing unit (CPU)

The control unitcontrol unit The control unit of the central processing unit coordinates execution of the program instructions by communicating with the arithmetic/logic unit and memory--the parts of the system that actually execute the program.control unit

The Arithmetic/Logic Unit (ALU)Arithmetic/Logic Unit (ALU) The arithmetic/logic unit (ALU) contains circuitry that executes the arithmetic and logical operations. The unit can perform four arithmetic operations: addition, subtraction, multiplication, and division. Its logical operations usually involve making comparisons that test for three conditions: the equal-to condition, the less-than condition, and the greater-than condition. The computer can test for more than one condition at once, so it can discern three other conditions as well: less than or equal to ( =), and less than ( ).arithmetic/logic unit (ALU)arithmetic operations logical operations equal-to conditionless-than conditiongreater-than condition

How the CPU Executes Program Instructions? The central processing unit follows four main steps when executing an instruction (I-time, E-time):I-timeE-time I-timeI-time (Instruction time) (1) Fetch: fetches--gets--the instruction from memory. (2) Decode: decodes the instruction and gives instructions for the transfer of appropriate data from memory to the ALU. E-timeE-time (Execution time) (3) Execute: directs the ALU to perform the actual operation on the data. (4) Store: directs the ALU to store the result of the operation in memory or a register.

How the CPU Executes Program Instructions?

Data Representation: Since a computer can recognize only whether electricity is on or off, data is represented by an on/off binary system, represented by the digits (1 and 0).binary system

Binary system Each 0 or 1 in the binary system is called a bit (binary digit).bit A group of bits (usually 8 bits) is called a byte, which usually represents one character of data, such as a letter (from A-Z), digit (0-9), or special character Memory capacity was once expressed in Kilobytes (KB or K). One kilobyte equals 1024 bytes. A Megabyte (MB), about one 1024 KB.Kilobytes (KB K) Megabyte (MB) Is used today to express memory size. A Gigabyte (GB) equals about 1024 MB.Gigabyte (GB) To express secondary storage size. A Terabyte (TB) equals about 1024 GB.

A computer wordword is the number of bits that make up a unit of data, as defined by the computer system.

ASCIIASCII Code A common coding scheme for representing characters is ASCII (American Standard Code for Information Interchange), which uses 8 bits per character. ASCII

The MotherboardMotherboard The motherboard, the flat board within the personal computer housing, holds the chips and circuitry that organize the computer's activities. The motherboard also holds expansion slots into which other circuit boards can be inserted to link peripheral devices to the processor.motherboard expansion slots

Microprocessor Microprocessors contain tiny transistors, electronic switches that may or may not allow current to pass through, representing a 1 or 0 bit, respectively.transistors

Microprocessor speeds measures 1. MegaHertz (MHz): Microprocessor speeds are usually expressed in megahertz, millions of machine cycles per second. 2. (MIPS), which stands for one Million Instructions Per Second. 3. megaflop, which stands for one million floating-point operations per second.

Random-access memory (RAM) Keeps the instructions and data for whatever programs you happen to be using at the moment.

A single in-line memory module (SIMM)single in-line memory module (SIMM) Is a plug-in board that contains memory chips.

RAM Types: RAM is often divided into two types: 1. Static RAM (SRAM), which is faster.(SRAM) 2. Dynamic RAM (DRAM), which is smaller and less expensive.(DRAM)

Read-only memory (ROM) Contains programs and data that are permanently recorded into this type of memory at the factory; they can be read and used, but they cannot be changed by the user. ROM is nonvolatile.