lesson 3 — how a computer processes data unit 1 — computer basics

Lesson 3 — How a Computer Processes Data

Unit 1 — Computer Basics

Lesson 3 – How a Computer Processes Data2

Objectives

Identify computer system components. Explain how the CPU works. Differentiate between RAM and ROM. Describe how data is represented.


Computer System Components

A computer system requires many components to do its job:– It requires some device or method to input data so it

can be processed.– It requires circuits and programs in order to process

the data.– It needs some type of output device to give the result

of its processing to the user.– It needs some mechanism for storing data.


Common System Components

This figure shows several devices that are common com-ponents of a com-puter system.


System Motherboard

Inside the case of a modern PC is the motherboard, which contains the electronic circuitry of the computer.

Components found on the motherboard include– The primary processing chip (CPU).– The memory chips.– Expansion slots for system interface cards.– Ports for connecting external devices.– BIOS chips that control system start-up.– The circuitry that enables all of these components to

communicate.


Example of a Motherboard

This figure shows the devices inside a PC case, including the motherboard, the power supply, and some storage devices.


The Central Processing Unit

The CPU is the brains of a computer system. The CPU is housed on a silicon chip that contains millions of

switches and circuits. The CPU has two primary sections:

– Arithmetic/Logic Unit (ALU) This section performs arithmetic and logical operations.

– Control Unit This section is the boss of the CPU and coordinates all activity

within the CPU. It uses programming instructions to control what actions the CPU performs and when it performs them.


A CPU Chip

This figure shows a CPU chip for a small computer. The CPU determines which of the millions of switches that it contains should be turned on or off by processing program statements that tell it what to do.

Computer programs are written in programming languages, and each program statement causes one or more actions to occur in the CPU.


Computer Memory

Data being processed by a CPU is stored in system memory.

Memory consists of addressable locations within the machine that the computer can access directly.

Data stored in memory is not permanent. If the power fails, everything in memory is lost.– Data must be stored on a disk or some other device

when not being processed so it is not lost each time the computer shuts down.


Types of Memory

– RAM – Random Access Memory This is short-term memory where data is processed while a

program is running. Data stored here can be accessed and modified as needed. This type of memory loses any data it holds if the computer is shut

down.– ROM – Read-Only Memory

ROM is memory placed on the motherboard by the manufacturer and contains instructions that tell the computer how to start itself.

This data cannot be accessed or modified by application programs.

The contents of this memory are not lost when the computer is shut down.


The Instruction and Execution Cycles

This figure illustrates the basic cycle involved in process-ing a program statement. This process is called the instruction cycle. The amount of time required to complete the instruction cycle is referred to as the execution cycle.


The Machine Cycle

The instruction cycle and one or more exe-cution cycles create a machine cycle, as shown here. Machine cycles are measured in microseconds, and the faster your computer can process machine cycles, the faster it can process data.


Computer System Controllers

A PC motherboard also contains several controllers.

Controllers are devices that control the transfer of data between the computer and peripheral devices.

Common peripheral devices include a mouse, a monitor, a printer, a keyboard, and so on.

Controllers are usually found on a single chip which can handle all usual devices.


Ports and Expansion Slots

Serial and parallel ports are used to connect peripheral devices to the computer circuitry.

– Serial devices (mice/monitors) transmit data one bit at a time.– Parallel devices (printers) transmit data several bits at time.

USB is a newer, high-speed method of connecting devices and is beginning to replace serial and parallel ports.

Expansion slots are electrical connections in the motherboard that can accept circuit cards to perform specific functions.

– These are commonly used to plug in sound cards, video cards, scanners, and other devices.


A Typical Expansion Card

It has electrical prongs along the bottom to plug into the expansion slot and make an electrical connection to the main board.

This port sticks out of the back of the PC case and is used to attach the device that this card controls.


Data Representation

Data is stored in a computer in binary format as a series of 1s and 0s.

Computers use standardized coding systems (such as ASCII) to determine what character or number is represented by what series of binary digits.

Data is stored in a series of 8-bit combinations called a byte.

Every letter, number, punctuation mark, or symbol has its own unique combination of ones and zeros.


Summary

Just about all computers perform the same general options: input, processing, output, and storage.

Input, output, and processing devices grouped together represent a computer system.

The motherboard is the center of all processing. The motherboard contains the CPU, memory,

and basic controllers for the system.


Summary (continued)

The motherboard also contains ports and expansion slots.

The central processing unit is the brains of the computer.

The computer is given instructions through computer programs.

The CPU has two main sections—the arithmetic logic unit and the control unit.


Summary (continued)

All calculations and comparisons take place in the ALU.

The control unit coordinates the CPU activities. The motherboard contains different types of

memory. Random access memory is volatile and is used

to store instructions, data, and information temporarily.


Summary (continued)

Read-only memory is nonvolatile and is used to store instructions, data, and information temporarily.

The machine cycle is made up of the instruction cycle and the execution cycle.

A controller is used to control the transfer of data between the computer and peripheral devices.

Peripheral devices are connected to the computer through serial and parallel ports.


Summary (continued)

The Universal Serial Bus is a new standard expected to replace serial and parallel ports.

Expansion boards are used to connect specialized peripheral devices or to add more memory to the computer.

The ASCII code is a standard code used to represent the alphabet, numbers, symbols, and punctuation marks.

lesson 3 — how a computer processes data unit 1 — computer basics

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