Chapter 4

The Central Processing Unit: What goes on Inside the

Computer

Components of the CPU

Control Unit (CU) Directs system operations Communicates with the ALU and

memory

Arithmetic Logic Unit (ALU) Performs calculations

ALU Operations Arithmetic operations

Addition (+) Subtraction(-) Multiplication (×) Division (÷)

Logical operations Equal-to (=) Less-than (<) Greater-than (>)

Components of the CPU

Registers Temporary storage High speed Not part of memory

System clock Controls speed of processing Does not keep date/time

Instruction Execution

Machine cycle: Fetch – get an instruction Decode – interpret, then get data

from memory Execute – perform the instruction Store – move the result to memory or

a register

Data Representation Bit (Binary Digit)

ON (1) OFF (0)

Byte 8 bits Stores one character

Word Number of bits processed at one time The size of a register 32 or 64 bits for PCs

Coding Schemes

Assigns a number to each characters ASCII – 1 byte per character

Used on PCs and larger computers 256 possible characters

EBCDIC – 1 byte per character Used on IBM mainframes 256 possible characters

Coding Schemes

Unicode – 2 bytes per character Allows characters from languages

other than English Used by Java, a programming

language for the web 65,536 possible characters

Memory Types

RAM Random Access Memory Volatile – lost if the power goes off Often called main memory

ROM Read Only Memory Non-volatile Required for booting the computer

Memory Types

CMOS RAM Stores info about computer hardware Requires battery power

Memory

Each location has unique address Fast access regardless of location Programmers use names instead

of address numbers

Memory and Storage Capacities

Kilobyte (KB or K) – approx. one thousand bytes Exactly 1024 bytes

Megabyte (MB) – approx. one million bytes Gigabyte (GB) - One billion bytes Terabyte - One trillion bytes

System Unit

the box or case that houses the electronic components of the computer

Inside the system unit you find: CPU Memory Motherboard Power supply And much more

System Unit’s Motherboard CPU Memory Expansion slots Connections to

other components

Microprocessors Intel

Pentium Celeron Xeon, Itanium

Intel-compatible Cyrix, AMD

Non-Intel PowerPC Alpha

System Bus

Copper lines on the motherboard For example, from memory to CPU Transports data and instructions Bus width Bus speed

Expansion Buses

Expansion boards Ports

Serial ports Parallel ports

Universal Serial Bus (USB) PC Card Bus

Measuring Computer Time

Millisecond—one thousandth of a second

Microsecond—one millionth of a second

Nanosecond—one billionth of a second

Picosecond—one trillionth of a second

Computer Processor “Speed”

The frequency of pulses from the system clock

MHz – megahertz, one million pulses (ticks) per second

GHz – gigahertz, one billion pulses per second

The higher the number, the faster the CPU can process instructions.

PC Processor “Speed”

Common processor frequencies 1.53 Gigahertz ( 1,530,000,000 ticks

per second ) 1.8 GHz 2.2 GHz 2.8 GHz

Cache Very fast memory Stores frequently used instructions Level 1 - Built into the processor

chip Level 2 - Separate chips

Usually 256 KB or 512 KB Cheaper than level 1

Most PCs have Level 2 cache

Flash Memory

Nonvolatile RAM Uses

Cellular phones Digital cameras Handheld computers

Some of the factors affecting overall speed of a computer

CPU speed Amount and speed of RAM Speed and size of bus lines Amount and speed of L1 and L2

cache Register size (Word size)

Shopping for a Computer

1. Decide what software you will need.

What do you want to do with the computer?

Email? Web browsing?Word Processing? Spreadsheet?Make CD’s? Edit photos or movies????

Shopping for a Computer

2. Determine the types of hardware needed for the software. Make a list of hardware specifications.

Email, Web browsing, and other Internet related software requires a modem or other hardware to connect to the Internet.

Shopping for a Computer

Word processing, spreadsheet, and presentation graphics don’t require a super-fast processor or much memory.

Want to print your document? You will need a printer.

Shopping for a Computer

Large databases, lots of music files, photos, or videos require a large amount of hard drive space and a lot of memory.

Want to make your own music CDs?You need a writable CD drive.

Shopping for a Computer

If you use statistical or mathematical, photo editing, or video editing software, you’ll need a fast processor and a lot of memory.

Want to watch movies on your computer? You’ll need a DVD drive and a fast processor.

Shopping for a Computer

3. Set a price range. Typical PC’s sell from $ 500 to $ 2000

Some software will come with the system, but you may need to purchase additional software to meet your needs.

The cheapest computer is usually not the best choice.

Shopping for a Computer

4. Learn about manufacturers, their reputations, service and support provided, etc.

Instructor’s Top 5:Hewlett-Packard (Compaq)DellGatewayIBMSony

Shopping for a Computer

5. Compare available systems

Sunday paper adsStore flyersTV adsManufacturer’s web sites

Watch the fine print. “after rebates”, “monitor sold separately”, “when you sign up for MSN”, are common.

This Week’s Ad Celeron Processor: 2.4 GHz (gigahertz) Memory: 256 MB (megabytes) Hard drive: 80 GB (gigabytes) Other drives: DVD and CD-RW Monitor: 17” color Printer: color inkjet Manufacturer: Medion $829.97 ($549.97 after rebates)

End of Chapter Questions

1. The electrical circuitry that executes program instructions is the ______.

a. registerb. operatorc. central processing unitd. bus line

End of Chapter Questions

2. The entire computer system is coordinated by ___.

a. the ALUb. the control unitc. registersd. arithmetic operators

End of Chapter Questions

5. The primary storage unit is also known as _____.

a. a registerb. Mass storagec. Secondary storaged. memory

End of Chapter Questions

8. Computer operations are synchronized by _____.

a. the CPU clockb. The binary systemc. megabytesd. E-time

End of Chapter Questions

12. A letter, digit, or special character is represented by a ______.

a. bitb. bytec. kilobyted. megabyte

End of Chapter Questions

14. _____ cache is built into the CPU chip.

a. L1b. L2c. externald. disk

End of Chapter Questions

16. The main circuit board in a personal computer is called the _____.

a. fatherboardb. motherboardc. ram/bus boardd. ASCII board