Understanding Computers, Ch.31 Chapter 3 The System Unit: Processing and Memory.

Understanding Computers, Ch.3 1

Chapter 3

The System Unit:

Processing and Memory


Learning Objectives

Understand how data and programs are represented to a computer and be able to identify a few of the coding systems used to accomplish this.

Explain the functions of the hardware components commonly found inside the system unit, such as the CPU, memory, buses, and expansion cards.

Describe how new peripheral devices or other hardware can be added to a PC.


Learning Objectives, Cont’d.

Understand how the computer system’s CPU and memory components process program instructions and data.

Name and evaluate several strategies that can be used today for speeding up the operations of computers.

List some technologies that may be used in the future PCs.


Overview This chapter covers:

How computers represent data and programs

How the CPU, memory, and other components are arranged inside the system unit

How the CPU works

Strategies to speed up a computer and create faster computers


Data and Program Representation

Computers today are mostly digital computers—devices that can only understand two states.

The two states of a digital computer are typically represented by 0s and 1s; that is, in binary form.

Computers do all processing and communications in binary form, so natural-language input and output are translated to and from binary by the computer.


The Binary Numbering System

We normally use the decimal numbering system, which uses 10 symbols (0, 1, 2, 3, 4, 5, 6, 7, 8, and 9).

Computers use the binary numbering system, which represents all numbers using just two symbols (0 and 1).



Coding Systems for Text-Based Data

ASCII and EBCDIC Fixed-length codes that can represent any single

character of data as a string of eight bits.

Unicode A longer (32 bits per character is common) code

that can be used to represent text-based data in virtually any written language.


Coding Systems for Other Types of Data

Graphics data—often stored as a bitmap which the color to be displayed at each pixel stored in binary form.

Audio data—waveform audio is common; MP3 compression makes audio files much smaller.

Video data—requires a great deal of storage space, but can be compressed.


Machine Language

Machine language is the binary-based code used to represent program instructions.

The basic set of machine language instructions that a CPU can understand is that CPU’s instruction set.

Most programmers rely on language translators to translate their programs into machine language for them.


Inside the System Unit

The system unit of a PC is the case that houses processing hardware and other hardware.

All of the hardware contained within the system unit is connected to the system board or motherboard.


CPU The CPU (central processing unit) does the vast

majority of processing for a computer.

CPUs contains a variety of circuitry and components and are connected to the motherboard.

Also called the processor or microprocessor.


CPU, Cont’d.

Processing speed (clock speed) is measured in megahertz (MHz) or gigahertz (GHz) and measures the number of clock ticks per second.

A computer word is a group of bits or bytes that a CPU can manipulate at one time.

Other factors that affect the speed of the computer include the amount of RAM and cache memory, bus width, and bus speed.


Memory: RAM RAM (random access memory) is the computer’s main memory and is

used to temporarily storage programs and data with which it is working.

RAM is volatile (erased when the power to the PC goes off).

RAM comes in a variety of types, speeds, and size. Types of RAM include:

DRAMSRAM

SDRAM

DDR SDRAMRDRAM

DDR-II SDRAM


Memory: Other Types

Cache memory—fast memory chips located on or close to the CPU chip (L1, L2, and L3).

Registers—high speed memory built into the CPU.

ROM (read-only memory)—non-volatile chips inside which data or programs are stored.

Flash memory—non-volatile memory that can be erased and reused. Used both within the PC and for portable storage media (e.g digital cameras).


Buses

Buses are electronic paths that data travels around on a computer system.

Internal buses move data around within the CPU.

Expansion buses establish links with peripheral devices. ISA, PCI, AGP, USB, FireWire.


Expansion Slots and Cards

Expansion for desktop PCs. Expansion cards can be inserted into expansion

slots on the motherboard. Some external devices can be plugged into existing

USB or FireWire ports without adding another expansion card.

PC cards—used with notebook PCs.

Expansion for handhelds and mobile devices—can have proprietary, PC card, or SDIO slot.


Ports

Connectors to which devices can be attached.

Common ports: Serial

Parallel

SCSI

USB

FireWire

Network

Keyboard

Mouse

Monitor

Modem

MIDI

IrDA

Game


How the CPU Works

The CPU is a collection of electronic circuits and components.

Impulses from an input device passes through RAM and enters the CPU via a system bus.

Within the CPU the impulses move through the circuits and components to create new impulses.

Eventually, a set of electronic impulses leaves the CPU for an output device.


Typical CPU Components

Arithmetic/logic unit (ALU)

Control unit

Registers

Prefetch unit

Decode unit

Internal cache

Bus interface unit


The System Clock and the Machine Cycle The system clock synchronizes the computer’s

operations.

The machine cycle is the series of operations involved in the execution of a single, machine-level instruction. Fetch Decode Execute Store


Making Computers Faster Now and in the Future Speeding up your system today.

Add more memory.

Perform system maintenance.

Buy a larger or second hard drive.

Upgrade your Internet connection.

Upgrade your video card.

Upgrade your CPU.


Summary Data and program representation

Inside the system unit

How the CPU works

Making computers faster now and in the future

Understanding Computers, Ch.31 Chapter 3 The System Unit: Processing and Memory.

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