Chapter 4
The Central Processing Unit: What
goes on Inside the Computer
Components of the CPU
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Control Unit (CU)
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Directs system operations
Communicates with the ALU and memory
Arithmetic Logic Unit (ALU)
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Performs calculations
ALU Operations
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Arithmetic operations
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Addition (+)
Subtraction(-)
Multiplication (×)
Division (÷)
Logical operations
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Equal-to (=)
Less-than (<)
Greater-than (>)
Components of the CPU
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Registers
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Temporary storage
High speed
Not part of memory
System clock
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Controls speed of processing
Does not keep date/time
Instruction Execution
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Machine cycle:
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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
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Bit (Binary Digit)
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Byte
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ON (1)
OFF (0)
8 bits
Stores one character
Word
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Number of bits processed at one time
The size of a register
32 or 64 bits for PCs
Coding Schemes
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Assigns a number to each characters
ASCII – 1 byte per character
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Used on PCs and larger computers
256 possible characters
EBCDIC – 1 byte per character
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Used on IBM mainframes
256 possible characters
Coding Schemes
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Unicode – 2 bytes per character
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Allows characters from languages other
than English
Used by Java, a programming language for
the web
65,536 possible characters
Memory Types
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RAM
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Random Access Memory
Volatile – lost if the power goes off
Often called main memory
ROM
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Read Only Memory
Non-volatile
Required for booting the computer
Memory Types
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CMOS RAM
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Stores info about computer hardware
Requires battery power
Memory
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Each location has unique address
Fast access regardless of location
Programmers use names instead of
address numbers
Memory and Storage
Capacities
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Kilobyte (KB or K) – approx. one thousand bytes
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Exactly 1024 bytes
Megabyte (MB) – approx. one million bytes
Gigabyte (GB) - One billion bytes
Terabyte - One trillion bytes
System Unit
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the box or case that houses the
electronic components of the computer
Inside the system unit you find:
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CPU
Memory
Motherboard
Power supply
And much more
System Unit’s Motherboard
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CPU
Memory
Expansion slots
Connections to other
components
Microprocessors
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Intel
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Intel-compatible
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Pentium
Celeron
Xeon, Itanium
Cyrix, AMD
Non-Intel
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PowerPC
Alpha
System Bus
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Copper lines on the motherboard
For example, from memory to CPU
Transports data and instructions
Bus width
Bus speed
Expansion Buses
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Expansion boards
Ports
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Serial ports
Parallel ports
Universal Serial Bus (USB)
PC Card Bus
Measuring Computer Time
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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”
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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”
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Common processor frequencies
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1.53 Gigahertz ( 1,530,000,000 ticks per
second )
1.8 GHz
2.2 GHz
2.8 GHz
Cache
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Very fast memory
Stores frequently used instructions
Level 1 - Built into the processor chip
Level 2 - Separate chips
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Usually 256 KB or 512 KB
Cheaper than level 1
Most PCs have Level 2 cache
Flash Memory
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Nonvolatile RAM
Uses
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Cellular phones
Digital cameras
Handheld computers
Some of the factors affecting
overall speed of a computer
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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?
???
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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)
Dell
Gateway
IBM
Sony
Shopping for a Computer
5. Compare available systems
Sunday paper ads
Store flyers
TV ads
Manufacturer’s web sites
Watch the fine print. “after rebates”, “monitor sold
separately”, “when you sign up for MSN”, are
common.
This Week’s Ad
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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. register
b. operator
c. central processing unit
d. bus line
End of Chapter Questions
2. The entire computer system is
coordinated by ___.
a. the ALU
b. the control unit
c. registers
d. arithmetic operators
End of Chapter Questions
5. The primary storage unit is also known
as _____.
a. a register
b. Mass storage
c. Secondary storage
d. memory
End of Chapter Questions
8. Computer operations are synchronized
by _____.
a. the CPU clock
b. The binary system
c. megabytes
d. E-time
End of Chapter Questions
12. A letter, digit, or special character is
represented by a ______.
a. bit
b. byte
c. kilobyte
d. megabyte
End of Chapter Questions
14. _____ cache is built into the CPU
chip.
a. L1
b. L2
c. external
d. disk
End of Chapter Questions
16. The main circuit board in a personal
computer is called the _____.
a. fatherboard
b. motherboard
c. ram/bus board
d. ASCII board