- Cases are offered in two styles, desktop and tower. Today the tower
type is predominant. It stands upright and is much taller than it is
wide. It is usually placed on the floor next to, or under a desk. The
desktop has a pizza box profile and usually sits on the desktop.
- Tower cases are offered in two basic sizes, one that can fit
ATX (12" wide) motherboards and one that can accommodate ATX mini (8.5"
wide) motherboards. The number of drive bays offered also varies
depending on manufacturer.
- The motherboard and power supply mount to the floor at the rear
of the case. The drives (hard, floppy and CD/DVD) mount in enclosures
called drive bays at the front of the case.
- Cases run from $20 to $70 depending on size (ATX or ATX mini), number of drive bays and the wattage of the power supply.
The motherboard is the main circuit board in a PC. It contains all the circuits and components that run the PC.
Major Components found on the motherboard are:
- CPU - the Central Processing Unit is often an
Intel Pentium or Celeron processor. It is the heart of
every PC. All scheduling, computation and control occurs
here.
- BIOS - Basic Input Output System is a non-volatile
memory that contains configuration information
about the PC. It contains all the code required for the CPU to
communicate with the keyboard, mouse video display, disk drives
and communications devices.
When a PC is powered on it uses the BIOS 'boot code' to set up many required functions that bring the PC to a point where it is ready to work.
- RTC - the Real Time Clock chip keeps date, day
and time in a 24 hour format just like your watch. The PC
uses this clock to 'time stamp' files as they are created
and modified. When you print a file it time stamps the
pages as they are printed.
- Chip Set - these are large chip(s) that
integrate many functions that used to be found in separate
smaller chips on the motherboard. They save space and cost.
The functions performed by these chip sets often broken into two devices with one providing an interface from the CPU to the memory and the other providing controllers for IDE, ISA, PCI and USB devices (see below).
- Power - A 20 pin connector accepts a plug from
the power supply. This plug carry DC power to all the circuits
on the motherboard.
- Keyboard - A Mini-din 6-pin (round) connector
found at the back of the motherboard is where the keyboard
plugs in.
- Mouse - A Mini-din 6-pin connector found next to
the keyboard connector is where the where the mouse plugs
in.
- Display - This connector is not integrated into
the motherboard but is included in this list since its
function is absolutely necessary. It is a 15-pin, D-shell
type connector found on a video card that plugs into the
AGP connector of the motherboard (see below).
- IDE - stands for Integrated Drive Electronics.
These are 40 pin connectors that provide a place to connect
the ribbon cables from the drives (hard and CD/DVD). All data
between the motherboard and the drives is carried in these
cables. They are not accessible unless the PC cover is
removed.
- FDD connector - it is similar in function to the
IDE connector. It is a 34 pin ribbon connector that carries
data between the motherboard and any floppy drive installed
in the PC. Not accessible with PC cover on.
- DRAM - Dynamic Random Access Memory connectors
for SIMM and DIMM type memory modules. Not accessible with
chassis cover on.
- Serial Connectors
- Standard Serial Connector - This connector has
been around in PCs since they first appeared. It was
originally located on ISA expansion type cards (see below).
Today it is an integral part of newer motherboards. It is a 9-
pin, D-shell connector that allows you to connect external
devices with serial ports to your PC. The maximum data rate
is 115 KB/s.
- USB - Universal Serial Bus This is a relatively
new serial bus. Originally specified as low speed, 1.2
Mb/s, it was enhanced to full speed, 12Mb/s. The latest
version 2.0 is specified as high speed, 400 MB/s.
Someday USB will completely replace the standard serial connector that has been the workhorse serial port in earlier PCs. USB is now a standard connector on all new motherboards.
Unlike serial and parallel ports, the USB port is designed to power devices connected to it. The devices must be low power devices and must be able to reduce their current draw to less than 0.5uAmps when commanded to do so by the PC.
- Standard Serial Connector - This connector has
been around in PCs since they first appeared. It was
originally located on ISA expansion type cards (see below).
Today it is an integral part of newer motherboards. It is a 9-
pin, D-shell connector that allows you to connect external
devices with serial ports to your PC. The maximum data rate
is 115 KB/s.
- Parallel Connectors
- Centronix or Standard Parallel - This connector
has been around in PCs since they first appeared. It has
37-pins and is now integrated on new motherboards. It is
usually used to connect your printer to the PC and moves
data at about 1MB/s.
- SCSI - Small Computer System Interface moves
data at a maximum of up to 80Mb/s. It not integrated into
most PC motherboards. It can be added to a PC as an
Expansion card (see below). Some printers and hard disk
drives use SCSI interfaces.
- Centronix or Standard Parallel - This connector
has been around in PCs since they first appeared. It has
37-pins and is now integrated on new motherboards. It is
usually used to connect your printer to the PC and moves
data at about 1MB/s.
- Expansion Card Connectors - The CPU connects to
expansion card connectors through one of the chip set ICs
mentioned above. They are located on the motherboard near
the rear of the PC. These connectors allow special function
cards to plug into and work with the PC.
Before motherboards integrated the serial and centronix connectors they were found on expansion boards that plugged into ISA slots.
Most PCs have the following expansion connector types:
- ISA - Industry Standard Architecture connectors
have been around since 1980 and first appeared in the IBM
XT PC. This type of slot still appears on some newer
motherboards so that older expansion boards can still be
used. However, many motherboards no longer have ISA connectors
on them.
- PCI - Peripheral Component Interconnect is a
newer and faster interface that accepts all expansion cards
that have a PCI interface.
- AGP - Accelerated Graphics Port is a connector that is designed to work with video cards. Your video display plugs into and is controlled by one of these video cards. Many modern video cards offer enhanced 3D-graphics and fast, full motion video.
- ISA - Industry Standard Architecture connectors
have been around since 1980 and first appeared in the IBM
XT PC. This type of slot still appears on some newer
motherboards so that older expansion boards can still be
used. However, many motherboards no longer have ISA connectors
on them.
- A power supply is installed in the back corner of the
PC case, next to the motherboard.
- It converts 120vac (standard house power) into DC
voltages that are used by other components in the PC.
- A 20 conductor cable carries +5vdc, -5vdc +12vdc, -12vdc and ground
to the motherboard.
- Another pair of cables, each with four conductors and two 4-pin
connectors daisy-chained along it, carry +5vdc, +12vdc and ground
to the drives (hard, floppy and CD/DVD).
- Typical PC power supplies are rated at 200-250 watts and sell for about $50 - $75. Higher wattage supplies are available.
- The HDD installs in one of the 3-1/2 inch internal
drive bays in the PC. It is secured by machine screws.
- Data Transport: IDE (Integrated Drive Electronics) is a 40 pin ribbon cable
originally used to carry data to and from the host bus adapters on the
motherboard and the hard disk drive. This parallel bus was later renamed
PATA (Parallel Advanced Technology Attachment).
Drives with PATA interfaces are powered by a separate 4-pin cable from the power supply which carries +5v, +12v and ground.
Since 2009 SATA (Serial Advanced Technology Attachment) has replaced PATA in consumer and laptop PC's. It is a very fast serial bus and uses only 7 lines for data transport which is huge reduction from the 40 lines PATA requires.
SATA drives use a separate 15 pin connector for power and receive +5v, +3.3v, +12v and ground from the power supply.
- Data Storage is maintained magnetically on multiple rigid disks
that are stacked up like pancakes. Small arms with magnetic
pickups move rapidly back and forth across the top and
bottom surface of each disk in the drive. The sensors float
just a few microns above the rotating disk surface and can
read and write data (ones and zeroes) at very high rates.
- Most commercially available hard drives rotate at 5400
or 7200 RPM (revolutions per minute) which translates to 90
or 120 revolutions per second respectively. The data
transfer rate from the drive to the motherboard is 33
Mbytes/second in bursts. Newer drives are capable of higher
speeds up to 66 Mbytes/sec. To use this faster drive, the PC
must have an ATA/66 interface that is capable of keeping up
with it.
- A 40 Gbyte (Gigabyte) drive in 2004 sold for about $100. In 2012 a 1 Tbyte (Terabyte) drive sells for the same or slightly less and has 25 times more storage capacity!
Monitor
CRT Monitors
- Up until recently, CRTs (Cathode RayTubes) were the only type
of displays for use with desktop PCs. They are relatively big
(14" to 16" deep) and heavy (over 15 lbs).
- They are available in screen sizes from 14" to 21". A
17" display means that it is 17" measured diagonally from
one corner of the tube to the other. The actual viewing
area is smaller than 17" (about 16") since the electron gun
can't sweep completely to the tube edge.
- CRTs send a stream of electrons at the screen, which is
charged to about 25,000 volts. As they strike it they cause
phosphor on the backside of the screen to glow creating
light which you see. The electron stream is sweep back and
forth and up and down at about 60 sweeps per second and
turned off and on at the right time to make text and
graphics images appear.
- They are powered by standard 1230Vac wall power.
- Data is transferred to the display on a cable with a
15-pin D-shell connector that plugs into a connector on the
video card which in turn plugs into one of the PC's
expansion slots.
LCD Monitors
- Liquid Crystal Display (LCD) technology has been used in laptops for
some time. It has recently been made commercially available as monitors
for desktop PCs.
- LCDs have no electron gun and are therefore not very deep like
CRTs. The text and images you see are created by a back light behind the
panel, that shines through pixels (picture elements). Each pixel is
made up of three chambers red, green and blue. The chambers in each
pixel must be opened enough and in the proper proportion to produce the
correct brightness and color.
- For an LCD to provide a screen resolution 1024 x 768 pixels
(SVGA), it must have 786,432 (1024 x 768) pixels. In TFT (Thin Film
Transistor) type LCDs, each pixel is controlled by a tiny transistor
that opens and closes the chambers in each pixel.
- Desk top LCD displays are powered by standard 120Vac wall power.
- Data is transferred to the display on a cable with a 15-pin connector that plugs into a mating connector on the video card seated in an expansion slot in the PC.
- The keyboard was the first input device developed
for the PC.
- The standard keyboard layout provides 104 keys organized as four groups:
- alphanumeric keys (A-Z, 0-9)
- location keys (home, end etc.)
- numeric keypad
- function keys (F1-F12)
- alphanumeric keys (A-Z, 0-9)
- In addition to the standard keys, some keyboards offer
functions such as volume control for speakers, web browser
functions and power management.
- Data is transferred to the PC over a short cable with a
circular 6-pin Mini-din connector that plugs into the back of the
motherboard.
- Standard keyboards sell for $7 to $30 depending on the
feature set.
- There are wireless keyboards that communicate with a
pod that is plugged into the keyboard port. Radio Frequency
(RF) or InfraRed (IR) technology is used to communicate
between the keyboard and the receiver pod, which plugs into the PC.
Wireless keyboards are priced in the $40 to $45 range.
- Cherry Hill Inc. is releasing a keyboard that has an integrated Finger Tip sensor. Instead of having to type in passwords to access the PC a successful fingerprint match allows entry in to the PC or specific programs.
The mouse is the most common 'pointing device' used in PCs. Every mouse has two buttons and most have one or two scroll wheels.
- By default the left button is used to select items.
The right button is assigned as a context or alternate menu.
A single wheel is normally set to scroll up and
down on the active page . If a second wheel is present, it is usually assigned to scroll left and right on the page.
- The button functions can be reassigned by going to Control
Panel > Mouse > Buttons tab.
- Data is transferred to the PC over a short cable with a
circular 6-pin Mini-din connector that plugs into the back of the
motherboard. This type of mouse sells for $10 to $25 depending
on the style, button and wheel configuration.
- Some versions of the mouse are wireless. They communicate with a receiver pod that is plugs into the mouse port. Radio Frequency (RF) or InfraRed (IR) technology is used for communication between the mouse and the pod. These sell in the $30 to $45 range.
There are two designs used in a mouse for detecting motion:
Track ball
This type of mouse uses a rolling (track) ball. As the mouse moves the ball rolls. The rolling motion is converted electronically into matching movements of the mouse pointer that moves across your video display.
The track ball mouse is rapidly becoming another casualty of rapidly changing technology. The optical mouse has pretty much replaced it. The track ball mouse is already becoming a thing of the past.
Optical
This mouse uses an InfraRed transmitter/receiver pair to optically detect the motion of the mouse. It has a number of advantages over the track ball mouse:
- No mouse pad is required.
- Can work on any flat surface
- No rolling track ball that collects and transfers dirt to the internal rollers, making them slip. When they do, your mouse pointer jumps around in an unpredictable and annoying way!
See the Easy Tips section of this web site for an explanation on how to clean a track ball mouse.
- Speakers and headphones are the primary audio output
devices for a PC.
- Some monitors have speakers built into their sides.
Other speakers are free standing.
- Passive speakers plug into and are powered directly
from the output signal provided by the 'speaker out' port
on the sound card.
- Active speakers amplify the sound signal from the sound card
using battery or rectified AC house power.
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