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					Type of Computers

There are four basic types of computers: PC (Personal Computer), Workstations,
Laptops, Servers.

The PC, or Personal Computer, is the most common category of
computers. This category would include your home PCs and most of your
business class PCs.

A workstation is a breed of computer which is a high performance
version of the PC. Workstation manufacturers took many of the high
speed and high availability components normally found in servers and
created a workstation PC which is a high performance version of the
original. Throughout the rest of this tutorial, you will find the word PC and the word
workstation used interchangeably, while technically there is a difference, we will
begin using “workstation” now as a word to describe a PC since the two are in the
same basic category.

Laptops are portable computers. Originally, laptops were large, heavy, short
battery life beasts. Nowadays, laptops (also referred to as notebooks) are
light, powerful, have good battery life, and serve as a desktop replacement
for many individuals (including myself).

A server is a machine developed to allow for file or print serving,
application hosting, or some other task usually involving many
simultaneous connections. Common features of servers include
redundancy, multiple drives, large amounts of memory, multiple
processors.

PDAs

A Personal Digital Assistant (PDA) is a commonplace item in many businesses and
            homes. Spurred by the success of Palm Pilots, the PDA industry has had
            tremendous growth in the past few years.

              A PDA is a device which allows an individual to keep their notes,
              email, schedule, small documents, and other information with them at
              all times. It is a useful device for record keeping and usually syncs with
              your computer to allow your contact list and emails to be "in sync" with
each other in your handheld and normal computers.

Palm Pilots are the most prevalent PDAs on the market, with a market share of about
30%.

Most PDAs are based on either the Palm operating system or the Microsoft PocketPC
         operating system.

           Palm Pilots present an interesting challenge to IT staff who are
           trying to support it. At one firm I worked at, we went through
           several different policies in regards to supporting PDAs.


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Originally, we would not support any PDA, though if a member of management were
to purchase one, we would support them individually. Eventually, we decided on a
standard and if anyone were to buy the standard PDA we would support it. This
allowed us to designate an expert (which coincidentally happened to be me) on PDAs
and be able to develop support procedures for the specific PDA we would support.

Types of PCs

There are several types of Personal Computers you should be aware of: small form
factor, minitower, midtower, full tower, desktop.

A small form factor is the smallest of the non-portable PCs. Typically lacking in
many expansion options, SFF computers are useful for situations which require the
smallest desktop style PC possible.

A minitower PC is a common household and business PC. It usually has some
expansion slots available (1-3) and one hard drive slot available. A typical minitower
PC has all of the ports built in to allow for more expansion cards.

A midtower PC is also a common business class machine. A midtower has more
expansion room than a typical minitower machine.

A full tower has the most expansion room and usually several hard drive bays open
for additional storage drives.

A desktop has probably been the most popular type of machine over the years. A
typical desktop machine is designed to lay flat on a desk or stand and contains 1-3
additional drive bays and 2-7 additional expansion slots available.




                                                                    Desktop
Small Form Minitower                                                Computer
Factor                           Midtower        Full        Size
           Computer
Computer                         Computer        Tower

Safety and Care

Before we launch into a lengthy tutorial on the insides of a computer we should
discuss care and safety when working inside a computer. I know you’re itching to
jump right in and start taking apart a computer at your desk but without the right
precautions, you can easily break your computer or worse, hurt yourself.



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Luckily for you – not only do you get to learn about safety and the precautions to take
when dealing with electronic equipment – but you also get to learn something useful
as these items are a portion of the CompTIA hardware service technician exam.

Electro-Static Discharge

            Electro-static discharge can cause damage to
            electronic components as you work on them. Note:
            ESD may be in several questions on the exam. ESD
            can be caused by static electricity your body picks
up as you move, rub against your clothing, or can be picked up
by things you touch.



While working on a computer or any components, you should always wear an ESD
wrist strap which grounds you. Also, it is recommended that you do not wear
synthetic clothing. Synthetic clothing can cause a buildup of static electricity as your
body rubs against it.

You should also always touch the case of the computer prior to touching components
inside, this will help to ground you.

The ESD wrist strap should not be used when working on monitors though, the stored
voltage can kill you.

When shipping or storing electronic components, you should send them in antistatic
bags. Antistatic bags do not conduct electricity and can be reused.

Generally speaking, if you are disassembling computers, the environment you are in
should be relatively dust free. It is also not recommended you work on electronic
devices in a room which is carpeted.

Parts of a PC

There are basic parts common to all PCs. Though they may look different, most of
these components function similarly among different brands, shapes, and sizes of
computers. This is a broad overview of the elements that makeup a PC, the System
Architecture course goes into much greater detail.

The Case

Typically, there are 5 types of cases for computers (from smallest to largest): small
form factor, minitower, midtower, desktop, full tower.

Depending on your use for the computer, different sizes serve different needs. A full
tower has the advantage of a large amount of expansion space. A small form factor,
on the other hand, does not have much expansion room, but does fit quite nicely in a
small office or area.



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The case is built to hold all of the components of a computer and protect from the
normal elements inside an office. If you pour coffee into your computer, the case will
not be able to protect it all that much, though from the normal every day occurrences,
a case does provide some protection. A case also is developed to allow for easy
cooling of the devices inside. Many elements of a computer become extremely hot
when operating and a case must be designed to handle airflow effectively to reduce
the temperature of its components.

The Power Supply

The power supply has the responsibility of converting power and providing it to the
components in the computer. The power supply converts 110 volt AC into four
voltages: +5 volts DC, -5 volts DC, +12 volts DC, -12 volts DC (ground).

The Motherboard

The Motherboard, sometimes referred to as the system
board or main board, is the central piece of all
computers. The motherboard contains the processor,
the RAM, and the expansion devices.

Storage Devices

A computer is not an effective tool if it doesn’t have a method to run software or store
data. Storage devices come in all shapes, sizes, and types. The purpose for a storage
device is to store and retrieve data.

Expansion Cards

Expansion cards allow you to expand the computer to add peripherals, communication
devices, or other functionality.

Monitor/Display

The monitor or display device is used to view the software which is running on the
computer.

CRT – Cathode Ray Tube. Most monitors built over the years are CRT monitors.
CRT is the standard in most televisions as well.

LCD – Liquid Crystal Display. LCD monitors have been widely used in laptops and
notebooks. Due to their high cost, they have mostly stayed off the desktop until
recently. With dropping LCD costs, more people are moving to LCD monitors with
the advantages of smaller occupied space, lower power requirements, and what many
believe is a higher quality picture (or possibly just easier on the eyes).




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System Board Overview

The system board, also referred to as the “main board” or “motherboard” contains all
of the elements that are central to the operation of the computer including the CPU,
expansion slots, memory, and components which connect to other devices.

                                  System Board Components

                                   The CPU (Central Processing Unit) is the central
                                   chip to the operation of the computer. The CPU
                                   processes the instructions from the software. A
                                   CPU can be from several different manufacturers,
                                   examples include a Pentium II, an AMD Athlon, or
                                   a PowerPC. CPU speeds are measured in
                                   Megahertz. The higher the Megahertz, the faster
                                   the chip (generally speaking, CPUs are also
measured in how many instructions per second it can perform and so a chip with a
lower MHz could work much faster than one with a higher MHz, though on the Intel-
compatible side of computing, the higher the MHz number, the faster the chip). For
example, a Pentium III running at 800 MHz is faster than a Pentium III running at 700
MHz.

Newer chips are measured in GHz (Gigahertz), which is simply 1000 MHz. A 1.2
GHz chip is 1,200 MHz.

The expansion bus allows the computer to be upgraded using different modules.
Expansion buses are made up with copper slots where a circuit board can plug into it.
The motherboard contains a bus clock which controls how fast information flows to
the expansion boards and back.

Memory, or more specifically RAM (Random Access Memory), is the place for
storages of software, computer instructions, and operations while the computer is
operating. RAM is a very fast storage location; though it loses all of its information
with a loss of power.




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The System Board

The System Board, or Motherboard, is discussed in great detail in the System
Architecture course. For the exam, you need to know the general layout of a
motherboard. Become familiar with the general layout of the system board. Here is an
example of a motherboard with common components referenced:




Expansion Bus

Expansion Bus Speed




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The different types of expansion busses operate at different speeds. The speed is
controlled by a bus clock. The speed is controlled so that the motherboard/CPU only
has to receive and transfer the amount of data it can handle or process at a given time.
For example, a slow processor may not be able to handle the amount of data a very
fast bus could transfer, so the data transfer speed is regulated to ensure the data does
not overload the processor.

Interrupts

Interrupts are commands from a device to signify to the computer to stop. Basically,
the operating system will continue running software code until the code is complete or
until it receives an interrupt request. In hardware, the interrupt request (e.g. IRQ) has
a value associated with it for each particular device.

DMA Channels

DMA Channels, or Direct Memory Access Channels, were designed to allow certain
devices direct access to the memory. In the original PC, the system was designed so
the CPU would control all access and act as the “traffic cop.” DMA was designed to
allow certain expansion cards or devices to bypass the “middle man” and access
memory directly. DMA was only used in ISA and its cousins EISA and VLB. PCI
expansion cards do not use DMA.

                                                           8-bit

                                    The 8-bit expansion bus operates at a maximum of 4.77 MHz
                                    (approx. 5 MHz), has eight interrupts, four DMA Channels,
                                    and one large 62 slot card.
8-bit                      Bus
(Click image for large version in
new window)
                                    ISA Bus

The ISA (Industry Standard Architecture) bus is a 16-bit bus
with a card slightly larger than the 8-bit. The 16-bit cards have
an extra piece extending beyond the 8-bit card length. This bus
                                                                  ISA               Bus
has 16 interrupts and 8 DMA channels. ISA also runs at 8 (Click image for large version in
MHz. ISA buses are backwards compatible with the 8-bit new window)
cards.



MCA Bus

The MCA (Micro Channel Architecture) bus was a proprietary bus designed by IBM.
It is a 16-bit or 32-bit bus and it’s clock speed is 10 MHz. It also offered software
configuration instead of dip switches and jumper settings.




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EISA

EISA (Extended ISA) bus borrowed a lot of features from the
MCA bus and expanded on them. It has a 32-bit bus and has
more I/O addresses (Input/Output addresses or memory
addresses). It also still uses the 8 MHz of the ISA bus to allow
for backwards compatibility.                                     EISA                                   Bus
                                                                             (Click image for large version in
                                                                             new window)




                                    Vesa Local Bus

                                    The VESA Local Bus (VLB) is a local bus type, meaning it is
                                    a bus which runs at the same speed as the processor. Typically,
                                    it is used for video to gain the advantage of the high speed of
                                    transfer of the processor. It is backwards compatible with the
VLBus                               ISA, but has an extra slot to make it 32-bits.
(Click image for large version in
new window)




PCI Bus

PCI (Peripheral Component Interconnect) Bus is the newest
and most advantageous type of all of the buses. It supports
both 32-bit and 64-bit data paths to be compatible with 486
and Pentium class processors. PCI is also processor
                                                            PCI                      Bus
independent, allowing it to operate in Macintosh, PC, and (Click image for large version in
RISC computers. PCI runs at 33 MHz and has a maximum new window)
throughput of 256 megabytes per second.



                                    AGP Bus

                                    AGP, or Accelerated Graphics Port, is a bus technology
                                    developed by Intel to support high speed video cards. The
                                    AGP interface uses the RAM in your computer to generate 3-
                                    D images and video very quickly.
AGP                        Bus
(Click image for large version in
new window)


PCMCIA Bus

PCMCIA (Personal Computer Memory Card Association) is the last type of bus we
will discuss. It is mainly used in laptops or other small computers and in some digital
cameras. PCMCIA comes in three types, cleverly called Type I, Type II, and Type III.

Type I cards are 3.3 mm thick. Type II cards are the most common type and are 5 mm
thick. Type III cards are mainly used for hard drives and are 10.5 mm thick.



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Summary of Expansion Busses

Bus Type                     Bus Size                       Speed (MHz)
8-bit                        8-bit                          4.77
ISA                          16-bit                         8 (10 in turbo mode)
MCA                          16-bit or 32-bit               10
EISA                         32-bit                         8
VESA Local                   32-bit                         Processor Speed
PCI                          64-bit                         Processor Speed
PCMCIA Card                  16-bit                         33 MHz

Storage Devices

There are several types of storage devices you should be aware of for the exam.

Hard Drives

There are three main types of hard drives (more specifically hard drive connection
types): IDE, EIDE, and SCSI.

IDE (Integrated Drive Electronics) is the original standard for hard drives for PCs.
IDE is the interface between the bus and the hard drive, based on the ISA 16-bit bus.
Originally, it was designed as a separate interface, but currently most computers
support EIDE with a built-in interface on the motherboard. A standard IDE drive
supports up to 528 MB of space.

                                     The EIDE (Enhanced IDE) interface was developed to
                                     overcome the 528 MB limit on hard drive size. The most
                                     common type of connector, EIDE also supports faster access,
                                     DMA, AT Attachment Packet Interface (ATAPI) for CD-
                                     ROM and tape drives, and support for additional drives. EIDE
EIDE                Connector can be added as an expansion board to older systems. Most
(Click image for larger version in a
new window)                          newer systems come with EIDE functionality built-in to the
                                     motherboard.

                           SCSI (Small Computer Systems Interface) is another standard
                           for hard drive connection. SCSI also has a variety of other
                           peripherals and storage devices which can take advantage of it.

                                     SCSI comes in three varieties: SCSI 1, SCSI 2, and SCSI 3.
                                     SCSI 1 supports up to 8 devices, 1 of which is required to be
                                     the controller card (so you can add 7 additional devices to the
SCSI 3 Cable                         controller). Unlike normal IDE or EIDE systems, most SCSI
                                     devices come in internal or external varieties and most cards
(Click picture for larger version in can support both. SCSI 2 (also known as Ultra-2), which is
a new window)
                                     more popular than SCSI 1, supports up to 16 devices (one of
which has to be the adapter card or controller) and supports a higher transfer speed.
SCSI 3 is sometimes referred to as Ultra-3 SCSI. Ultra-3 SCSI increases the


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throughput rate of the interface from 80 Mbps to 160 Mbps. The new standard for this
transfer rate is referred to as Ultra160/M.




                                                                             Max
                                                            Max Cable Max
                                                                             Number
                     SCSI Type                              Length    Speed
                                                                             of
                                                            (meters)  (MBps)
                                                                             Devices
                     SCSI-1                                 6                        5            8
                     SCSI-2                                 6                        5-10         8 or 16
                     Fast SCSI-2                            3                        10-20        8
                     Wide SCSI-2                            3                        20           16
                     Fast Wide SCSI-2                       3                        20           16
                     Ultra SCSI-3, 8-bit                    1.5                      20           8
                     Ultra SCSI-3, 16-bit                   1.5                      40           16
                     Ultra-2 SCSI                           12                       40           8
                     Wide Ultra-2 SCSI                      12                       80           16
                     Ultra-3 (Ultra160/m)
                                          12                                         160          16
                     SCSI

A SCSI chain (all of devices on a controller) must have a terminator at both ends.
The SCSI card often has a built-in terminator and a lot of present day SCSI devices
also have a switchable termination on the drive or device. SCSI drives are typically
more expensive than EIDE drives, but have higher access speed and allow for more
devices on one controller.




SCSI             2          Port
(Click picture for a large image in
                                      SCSI            2          Cable                        Internal                       SCSI
a new window)
                                      (Click picture for a large image in a   SCSI Terminator Cable
                                      new window)                             (Click picture for a large   (Click picture for a large
                                                                              image in a new window)       image in a new window



Preparing Your Hard Drive

The factory does a low level format on the hard drive prior to shipping it out which
organizes the hard drive into tracks and sectors. It is possible for you to perform a low
level format of a drive but highly not recommended. Low level formatting can
damage a hard drive and make it unusable.



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When you install a hard drive, there are several items you need to be aware of when
setting it up. There are three settings on hard drives: Master/Slave/Cable Select.
Master is used for the first hard drive, Slave for the second drive when you have two,
and Cable Select goes in the order on the EIDE cable.

EIDE interfaces allow two drives per channel. Most EIDE controllers have a primary
and secondary channel to allow for four total devices.

Before the installation of an operating system, you have to partition and format (high
level format) the hard drive. When you partition a drive, you setup different virtual
drives on the PC. Hard drives can have three primary partitions and 1 extended
partition. Extended partitions can have up to 23 logical partitions. On most computers,
you are able to setup a single partition if you wish. Commonly this becomes drive
"C:" in Windows (A: and B: are typically reserved for floppy disk drives).

CD-ROMs

CD-ROM (Compact Disc – Read Only Memory) was
developed by Sony and Phillips. It has a standard
capacity of 650 Megabytes of information and is
burned onto a disc using laser light.

CDs have expanded over the years and a typical CD-
ROM today can hold 700 MBs of information or 80
minutes of music.

Most typical home machines and some business-class PCs come with a CD-R or CD-
RW drive. A CD-R drive allows you to write once to a CD-R or CD-RW disc. A CD-
RW drive allows you to write once to a CD-R disc or many times to a CD-RW disc.

There are many advantages to using CD-Rs and CD-RWs to store data or backup
data. Cost per megabyte is very cheap on CD-Rs, most for pennies per megabyte. In
addition, CD media is fairly long lasting if you care for it.

CD media can become unreadable if you leave discs in sun or heat for too long or if
they become scratched.

CDFS (Compact Disk File System) is the type of filing system CD-ROMs use to store
information.

Tape Backup Devices

Typical backup drives connect via the parallel port, SCSI, ATAPI,
or USB ports.

There are several different competing tape formats you should be
aware of. QIC (Quarter Inch Format) is a format which either
comes in a 3.5” or a 5.25” hard plastic case. It can store from 40
Mb to 25 GB worth of data.



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Linear Tape-Open (LTO) is an open standard format developed by IBM, Hewlett-
Packard, and Seagate. LTO was developed to provide a standard among normally
proprietary tape backup systems. LTO format tapes come in a variety of sizes and
types.

The positive of tape is a large amount of storage for a low reusable cost. The
negatives of a tape are its access time – a tape starts at the beginning and moves to the
spot where the data is when retrieving information.

Tape devices are typically only used for backup situations.

Floppy Drives

In early home PCs, often the floppy drive was the only way to store and retrieve data
(though in my first computer – an Atari – I had a tape cassette recorder which stored
and retrieved somewhere in the neighborhood of 16K of a normal audio cassette).
Over the years, the floppy drive has stayed with us, though more as a leftover from
the early days than anything else.

A typical system with a floppy drive is a 3.5” drive which holds 1.44 MB.




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