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Ch
6 The System Unit


Competencies
page 148


Describe
the four basic types of system units.


Discuss
how a computer uses binary codes to represent data in electronic form.


Describe
each of the major system unit components.


Describe
microprocessors, including specialty processors.


Describe
the different types of memory.


Describe
expansion slots and boards.


Describe
the five principal types of expansion buses.


Discuss
the four standard ports.


Introduction
page 149



Differences in microcomputer power focus on speed,
capacity and flexibility.
Competent end users need to understand the functionality
of the basic components in the system unit, including the system board,
microprocessor, memory, system clock, expansion slots and cards, bus
lines, ports, cables, and power supply units.
Some terms:
Disk Drives: are secondary storage devices for saving
data, programs, and information.
Bus Lines: provide data pathways that connect various
system components
Power Supply Unit: converts Alternating Current (AC)
to Direct Current (DC) providing power to the system unit.
Systems Board: connects all system components to
one another.
System Unit: contains most of the computers electronic
components.
Memory: holds data, instructions, and information,
memory circuit boards plug into slots on the system board
Microprocessor: controls operations and performs
arithmetic and logical operations, microprocessor cartridges plug into
a special slot on the systems board.
Expansion Cards: allow external devices to connect
to and expand a computers capabilities, expansion cards plug into slots
on the systems board.
Expansion Slots: provide connections for expansion
cards to the system board.



System
Unit page 150



The System unit (aka system cabinet or chassis) is
a container that houses most of the electronic components that make
up a computer system.  Four basic types include:
Desktop system units: contain the systems electronic
components, secondary storage; input & output devices are located
outside the system unit.  Vertical units are called tower models.
Notebook system units (aka laptops): are portable
and much smaller.
Tablet PC system units: similar to notebooks with
a screen that allows input via a stylus.
Handheld computer system units (aka palm computers):
smallest and designed to fit into the palm of one hand.  Personal
Digital Assistants (PDAs) are the most widely used handheld computers.



Electronic
Data and Instructions page 152



Computers only recognize digital electronic signals.
Much information comes via analog signals: continuous
signals, which vary to represent different tones, pitches, and volume
such as our voices.
Computers must be able to convert analog signals
to digital for processing.
A binary system is used to represent computer data
and information.
Binary systems use two digits, 0 & 1.
Each 0 or 1 is called a bit short for binary digit.
Bits are combined into groups of eight bits called
bytes.
Each byte typically represents 1 character.



Binary
Coding Schemes



Characters are represented as a series of bits through
the use of a binary coding scheme.  Popular schemes include:
ASCII: American Standard Code for Information Interchange
the most widely used code for microcomputers.  It typically uses
an 8 bit encoding scheme, enough to handle 2^8th (256) different characters. 
An example for the letter A is 0100 0001.
EBCDIC: Extended Binary Coded Decimal Interchange
Code an IBM standard used for large computers.  It also uses
8 bits, but differs slightly from the ASCII coding scheme, e.g. A =
1100 0001
Unicode: a 16 bit (2 byte) code used to support international
languages.  It can represent 2^16th characters (65,536 characters)
When you press a key on the keyboard, the keyboard
hardware sends an electronic signal to the system unit, converting the
key such as the number 3 to the ASCII code of 0011 0011.



System
Board page 154



The system board (aka main board or motherboard)
is the communications medium for the entire computer system.  Every
component of the system unit connects to the system board.
A standard circuit board can contain:
Sockets: provide a connection point for small specialized
electronic parts called chips.
Chips (aka silicon chips, semiconductors, or integrated
circuits): consist of tiny circuit-boards etched on to squares of sand-like
material called silicon.