EN0129 PC and Network
Technology - 1
Semester One Week 2:
Case and Power Supply Unit
[Ref: www.pcguide.com & www.pctechguide.com]
Sajjad Shami
Adrian Robson
Gerhard Fehringer
School of Computing, Engineering & Information Sciences
Northumbria University
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Case
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Physical protection
Framework for components
EM screening
Cooling
Security
Power Supply Unit (PSU) often
integrated
• Form factors of motherboards vary
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Components
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Inside
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Case Sizes & Form factors
• tower or mid-tower cases
• preferably ATX form factor.
– Advanced Technology Extended
http://en.wikipedia.org/wiki/ATX
• smaller cases: smaller footprint: save space.
• larger cases: more room for expansion options,
easier working
• good mid-tower or full-tower ATX cases can be
paired with any ATX motherboard.
– £40 - £90.
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Case Style
• ATX case style
– set by motherboard manufacturers
– can last through several years of
motherboard upgrades
• note: some PC manufacturers, e.g. Dell,
use proprietary motherboards and case
designs
– have unique drilling patterns that connect the
motherboard to the case.
– not as easily upgraded.
• standard components: maximum upgrade
potential
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ATX .. Some detail
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ATX is a Motherboard Specification
written as a specification for the PC industry
designed to add value to the PC
defines a new PC form-factor that will allow PC
manufacturers to build products
– more cheaply
– improve ease of use and serviceability
– incorporate new and exciting I/O features with ease.
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ATX …contd.
• ATX form factor is essentially an AT motherboard rotated 90 degrees
within the chassis enclosure
– and a new mounting configuration for the power supply
• by doing this, the processor is relocated away from the expansion
slots
– allowing them all to hold full length add-in cards
• ATX defines a double height opening to the rear of the chassis
– which can be used to host a wide range of on-board I/O
• only the size and position of this aperture is defined
• this allows PC manufacturers to add new I/O features
• e.g.; TV input, TV output, joystick, modem, LAN, audio, etc.
• to systems that will help them differentiate their products in the marketplace
• and better meet the needs of end users
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ATX … effect on cost
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a change to the system form-factor is of little benefit if it doesn't reduce
overall system cost
ATX achieves this in a number of ways:
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1) by integrating more I/O down onto the board and better positioning the
hard drive and floppy connectors material cost of cables and add-in cards is
reduced
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2) by reducing the number of cables and components in the system,
manufacturing time and inventory holding costs are reduced and reliability
will increase
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3) by using an optimized power supply, it is possible to reduce cooling costs
and lower acoustical noise
– an ATX power supply, has a side-mounted fan, allows direct cooling of the
processor and add-in cards
– making a secondary fan or active heatsink unnecessary in most system
applications.
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ATX spec
• ATX specification is freely available to the whole industry
• current revision (2.0) incorporates feedback from the
many chassis and power supply vendors making ATX
products.
• the specification is available for download in Adobe
Acrobat format (357 KB).
• more information about the ATX specification and
vendors is available at
http://www.formfactors.org/developer/specs/atx/atxspecs.htm
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ESD Handling
• ESD = ElectroStatic Discharge (static electricity)
• worst when dry (winters)
• can destroy good PC components
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motherboards
memory chips
plug-in cards
bottoms of hard-drives
any PCB
• avoid carpet floors
• mats with grounding straps that ground the mat
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ESD tips
• three points to handling components safely:
• 1) draw off any static electricity that may be built up on your hands
before you touch a sensitive part
– should touch the metal PC case before touching the components
– metal will draw off any built-up charge
– even if you wear a grounding wrist strap, touch the PC case anyway as
an extra precaution
– touching the case’s power supply is recommended
• 2) touch the parts where they’re the least sensitive to being harmed
by ESD
– pick up mainboards/cards by the edges/metal parts.
• 3) always plan where you will place a component before removing it
from its electrostatic protection pouch
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Power Supply
• PSU comes with most cases
– has many power connectors
– to power the motherboard, hard drive(s), CD-RW
drives, ..
• ATX case: ATX power supply: ATX motherboard
• mains voltage is ac 240 Volts (UK)
• PC requires dc voltage
– need stable supply
– many components requiring different voltage levels
• ( drives, motherboard etc).
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Connectors
• twenty-pin ATX power
connector
– designed so that they can only be
plugged in one way
– provides power to the ATX
motherboard.
• newer ATX power supplies
– also have a special four-pin power
connector
– used with Pentium 4
motherboards
– not needed for AMD Athlon
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Thin-wire Connectors
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Power Switch (P SW):
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Reset Switch (Reset):
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goes on when the system is powered up.
HD LED:
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can be connected in either direction
if Ctrl+Alt+Del doesn’t work to reboot your hungup PC …
Power LED: (Light-Emitting Diode):
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can be connected in either direction
turns the PC on and off.
direction makes a difference
blinks when the hard drive is active.
Speaker connection:
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connects the small case speaker to the
motherboard.
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Voltage Levels
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Original PC PSU
+12V
+5V
-5V
-12V
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Later PSU’s
+12V
+5V
+3.3V
-5V
-12V
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+12 volts
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primarily for disk drive motors
also cooling fans
legacy motherboards did not use
modern motherboards use
passed on to expansion slots
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+5 Volts
• on older machines used for motherboard
and processors/memory
• now used for some motherboard
• passed to expansion slots
• also to drives for circuitry
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3.3 Volts
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new boards
processor
memory
AGP video cards
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-5 Volts
• early floppy controllers
• supplied to expansion slots (ISA)
• being phased out
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-12 Volts
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serial ports
only used by some circuits
current output limited
max current 1A
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Power Good Signal
• usually 5 Volt
• signifies that voltage levels are stable after
initial power up (takes time)
• power glitch will turn off power good
• resets PC
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Soft Power On
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early: PC mechanical switch
new: send signal from motherboard
software control
power required to tell PSU to switch on
+5V standby
always on (wake on LAN etc)
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Typical Power Consumption
Cards
• AGP Video Card 30 – 50W +3.3V
– Top range more power @ 1.5V or 0.8V
• Hard Drive 5W to 20W
• Fans 3W upwards
• Pentium 4 70W
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Totals
• for overall power supply wattage:
• add the requirement for each device in your system,
• multiply by 1.8.
• (The multiplier takes into account that today’s systems
draw disproportionally on the +12V output. Furthermore,
power supplies are more efficient and reliable when
loaded to 30% - 70% of maximum capacity.)
• http://www.distortionwave.com/Power.html
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UPS
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Uninterruptible Power Supply
a device that offers an extra protection to PC/equipment
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in case of an electrical mains power interruption, the UPS continues to feed the PC
during the time needed to save the work
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this feeding is provided by a battery that is always being charged while the mains
network is operating accordingly
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this battery has a set up which will hold the electrical feeding somewhere between 10
and 15 minutes
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do not use the UPS to work while there is no mains, but to have the opportunity to
save your work and turn the computer off
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do not connect other peripherals to the UPS, such as printers and scanners; only the
video display
PRACTICAL 1: PC Assembly: PREVIEW
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