Chapter 4
The Components of The System Unit
Matt Vanacore, Ryan Bratton, Thomas Bender
The System Unit
• Is a case that contains electronic
components of the computer used to
process data
– The motherboard is the main circuit board of
the system unit
• A chip is a small piece of semi conducting
material on which integrated circuits are
etched
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Processor
• Interprets and carries out the basic instructions that
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operate a computer
Contains a control unit and a arithmetic logic unit (ALU)
– Performs arithmetic operations, which is basic arithmetic
(addition, subtraction etc) and Comparison, which involves
comparing data with other data.
– Logical operations uses “and,” “or,” and “not.” It must verify
conditions.
• The control unit directs and coordinates most of the
operations in the computer.
• Both of these units work together to perform processing
operations
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Processor Cont.
• Registers are small high speed storage
locations that temporarily hold data.
• The computer relies on the System Clock
to control timing of all computer
operations.
– Each tick is a clock cycle, clock speed is
measured by the number of ticks per second.
– A hertz is one cycle per second
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Processor Cont.
• The four major manufacturers of Processors are
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Intel, IBM, AMD, and Motorola.
Most high performance computers use the
Pentium Processor, which is manufactured by
Intel.
AMD manufactures processors similar and
compatible to Intel, but not always as powerful
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Data Representation
• Two types of data representation
– Analog is a continuous signal that varies in strength and quality
• Humans
– Digital recognize only two discrete states, on and off
• Computers
• Binary system (bit) is a number system that has two
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unique digits, 0 and 1. This is the smallest unit of data
8 bites together form a byte, and this has enough
combinations to represent 256 individual characters
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Memory
• Consists of electronic components that store instructions
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waiting to be executed by the processor, data needed by
those instructions, and the results of processed data.
Three basic categories:
– Operating system and other system software that control or
maintain the computer and its devices
– Application programs that carry out specific tasks
• Word
– Data being processed by the application programs and resulting
information.
• RAM consists of memory chips that can be read from
and written to by the processor and other devices
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Memory Continued
• RAM has three different types
– Dynamic RAM are chips that must be reenergized constantly or they lose their
contents
– Static RAM chips are faster and more reliable
then any variation of DRAM chips
– Magnetoresistive Ram stores data using
magnetic charges instead of electrical charges
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Memory Cont.
• Memory Cache helps speed the process
of the computer because it stores
frequently used instructions and data.
– L1 cache is built directly into the processor.
– L2 cache is slightly slower than L1, but has
much larger capacity.
– L3 cache is a cache separate from the
processor chip on the motherboard.
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Memory Cont.
• ROM refers to every chip storing permanent data and
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instructions.
Firewall contains permanently written data,
instructions, or information.
A PROM chip is a blank ROM chip onto which a
programmer can write permanently.
EEProm chip allows a programmer to erase the
microcode with an electrical signal.
FLASH MEMORY is a type of none volatile memory that
can be erased electronically and re-written.
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Memory Cont.
• CMOS complimentary metal-oxide
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semiconductor technology because it provides
high speeds and consumes little power.
Memory Access Time is the amount of time it
takes the processor to read data, instructions,
and information from memory.
– Nanosecond is one billionth of a second
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Expansion Slots and Adapter Cards
• Expansion slide is a socket on the motherboard that can
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hold an adapter card.
An adapter card is a circuit board that enhances
functions of a component.
A peripheral is a device that connects to the system unit
and is controlled by the processor in the computer.
A sound card enhances the sound generating capabilities
of a personal computer by allowing sound to be input
through microphone and output through external
speakers.
A video card converts computer output into a signal that
travels through a cable to the monitor which displays an
image on the screen.
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ADAPTER CARDS CONTINUED
• A modem card is a communication device that enables
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computers to communicate via telephone lines, television
or other media.
A network card is a communications device that allows a
computer to access a network.
Plug and play is the computer automatically configuring
adaptor cards.
The pc card slot hold the pc card and the pc card is a
small device that adds memory, storage, sound, and
other communications.
Flash memory card is used to transfer data from mobile
devices to desk top computers.
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Ports and Connectors
• A port is a point at which a peripheral attaches to a
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system unit to send or receive data
A connector joins a cable to a peripheral
– Male connectors have one or more exposed pins
– Female connectors have matching holes to accept the pins on a
male connector
– A gender changer is a device that connects both male and male
or female and female
• Serial port is a type of interface that connects a device
to a system unit by transmitting data one bit at a time
• A parallel port is a interface that connects devices by
transferring more then one bit at a time.
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Ports and Connectors Continued
• USB ports can connect up to 127 different peripherals
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together with a single connector type
A USB hub is a device that plugs into a USB port on the
system unit and contains multiple USB ports
Firewire port is similar to a USB, but it transfers data
faster
MIDI port is the electronic music industries that defines
how devices such as sound cards represent sound
electronically
SCSI port is a high speed parallel port that allows you to
attach SCSI peripherals such as disc drives and printers
IrDA transmits signals to a computer via infrared light
waves
Bluetooth ports uses radio waves to transmit data
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Buses
• A bus allows the various devices both inside and
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attached to the system unit to communicate
Word size is the number of bits the processor can
interpret and execute at a given time
Data transmitted to memory travels from expansion bus
via the expansion bus and the system bus.
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Bays
• A bay is an opening inside the system unit
• In which you can install additional
equipment.
• Rectangular openings called Drive bays
typically hold disk drives.
• An external drive bay allows the user to
access the drive from outside the system
unit.
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Power Supply
• Power Supply is the component of the system unit that
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converts the wall outlet AC power into DC power.
An AC Adapter is an external power supply, which
modems, speakers, and tape drives get their power
from.
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Mobile Computers and Devices
• Two types of computing mobile devices are the tablet PC
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(Laptop) and a PDA (Palm Pilot).
The laptop is similar to the desktop in almost every way
except that many of the devices are part of the system
unit.
PDA’s have external keyboards and they often have
Bluetooth ports so they can communicate wirelessly.
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Putting It All Together
• People buying computers should how the components
of the system work because they influence many aspects
of the computer.
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