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CCT101: Chapter 2
The Components in the System Unit
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OBJECTIVES
Identify the components in the system unit and explain theirfunctions
Explain how the CPU uses the four steps of a machine cycleto process data
Compare and contrast various microprocessors on the market
today Define a bit and describe how a series of bits is used to
represent data
Differentiate between the various types of memory
Describe the types of expansion slots and expansion cards inthe system unit
Explain the difference between a serial and a parallel port
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THE SYSTEM UNIT
System unit
electronic components of the computer that are used to
process data
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CPU AND MICROPROCESSOR
CPU (processor)
Interprets and carries out the basic instructions thatoperate a computer
Microprocessor
Pentium processors
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The Components of CPU
The Control Unit
The Arithmetic/Logic Unit
Registers
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The Control Unit
A component of the CPU that directs and coordinates
most of the operations in the computer
Fetch - get the next instruction from
memory
Decode - translate the instruction
Execute - carry out the command
Store - write the result to memory
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The Control Unit
Instruction time or I-Time
The times it takes to fetch
Execution time or E-Time
The times it takes to decode and execute
Speed is measured in MIPS (million instructions per
second)
Current PCs can process more than 300 MIPS
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The Arithmetic/Logic Unit
Performs the execution part of the machine cycle
Arithmetic (addition, subtraction, multiplication,
division)
Comparison (greater than, equal to, less than)
Logical (AND, OR, NOT)
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Registers
Temporary storage locations used by the CPU
Storing location of where instruction was fetched Storing an instruction while it is being decoded
Storing data while the ALU processes it
Storing the results of a calculation
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Intel Pentium
CPU numbers could not be trademarked
Intel identify their microprocessor with names
AMD (Intel-compatible)
Same internal design or architecture as Intel Perform same function
Less expensive
Motorola PowerPC
Used in Apple Macintosh and Power Macintosh Systems
Increased the speed of processor
Alpha
Used primarily in workstations and high-end servers
Microprocessor Comparison
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Types of MICROPROCESSOR
Coprocessors
Special processor chip or circuit board designed to
assist the processor in performing specific tasks
Floating-point coprocessor
Math or numeric coprocessor
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Types of MICROPROCESSOR (cont.)
Parallel Processing
Using multiple processors simultaneously to execute a
program
Speeds execution
Requires special software
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DATA REPRESENTATION
Analog vs. digital
Digital
Two states
Binary number system
Combination of ones and zeroes represent
characters
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DATA REPRESENTATION
ASCII vs. EBCDIC
Sufficient for English and Western European languages
Unicode often used for others
Sending a character from the keyboard to the
computer
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MEMORY
Used to store data, instructions, and information
The operating system and other system software
Application programs
Data being processed by application programs
Bytes are stored at specific locations or
addresses
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MEMORY (cont.)
Size of memory is measured by the number of bytes
available
Kilobyte - 1,024 bytes
Megabyte - 220 bytes
Two memory types
Volatile
Nonvolatile
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MEMORY RAM
Random access memory The memory chips in the system unit
When the computer starts, operating system filesare loaded from a hard disk into RAM
Dynamic RAM (DRAM) Must be energized constantly or it loses its contents
Synchronous DRAM (SDRAM) Much faster than DRAM because it is synchronized to
the system clock
Static RAM (SRAM) Is faster and more reliable than any form of DRAM
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MEMORY RAM (cont.)
Configuring RAM
The more RAM, the more programs and files a computer can
work on at once
Software usually tells you how much RAM is required
Necessary RAM depends on what type of work the computer is
used for
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MEMORY (ROM)
Read-only memory
Cannot be modified
Contents not lost when the computer is turned off
Programmable read-only memory (PROM) Is a blank ROM chip that can place items permanently
The instructions used to program a PROM chip are called
micro-code
Flash Memory Non-volatile, but can be erased and reprogrammed
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MEMORY (CMOS)
Complementary metal-oxide semiconductor
Stores configuration information about the computer
such as type of disk drives, keyboard, and monitor Uses a battery to retain the information when the
computer is turned off
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MEMORY
(Memory Access Times)
Speed at which the processor can access
data from memory directly
Measured in nanoseconds (ns) which is one
billionth of a second
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EXPANSION SLOTS AND EXPANSION
CARDS An opening, or socket, where a circuit board can beinserted into the motherboard
Add new devices or capabilities to the computer
Three common types Video card
Sound card
Internal modem
Plug and Play Computers capability to automatically configure expansion cardsand other devices they are installed
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PORTS
Used to connect external devices to the system unit
Most located on the back of the system unit
Many types of connectors Some connectors are on the computer when purchased, others
added with expansion slots
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PORTS (Serial Ports)
Transmits one bit of data at a time
Used to connect devices that do not require fast
transmission rates
Mouse
Keyboard
Modem
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PORTS (Parallel Ports)
Connect devices that can transfer more than one
bit at a time
Usually used for printers Two newer types
EPP (Enhanced Parallel Port)
ECP (Extended Capabilities Port)
EPP and ECP use the same connector as parallel port,
but are more than ten times faster
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