en01291 en0129 pc and network technology - 1 sajjad shami adrian robson gerhard fehringer school of...
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EN0129 1
EN0129 PC and Network Technology - 1
Sajjad ShamiAdrian Robson
Gerhard Fehringer
School of Computing, Engineering & Information SciencesNorthumbria University
Semester One Week 2: Case and Power Supply Unit
[Ref: www.pcguide.com & www.pctechguide.com]
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Case
• 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
• 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• 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:
• 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
• 2) by reducing the number of cables and components in the system, manufacturing time and inventory holding costs are reduced and reliability will increase
• 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– 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• Power Switch (P SW):
– can be connected in either direction – turns the PC on and off.
• Reset Switch (Reset): – can be connected in either direction – if Ctrl+Alt+Del doesn’t work to reboot your
hung-up PC …
• Power LED: (Light-Emitting Diode):– goes on when the system is powered up.
• HD LED: – direction makes a difference– blinks when the hard drive is active.
• Speaker connection: – connects the small case speaker to the
motherboard.
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Voltage Levels
• Original PC PSU• +12V• +5V• -5V• -12V
• Later PSU’s• +12V• +5V• +3.3V• -5V• -12V
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+12 volts
• 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
• 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
• 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
• 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 ConsumptionCards
• 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• Uninterruptible Power Supply• a device that offers an extra protection to PC/equipment
• in case of an electrical mains power interruption, the UPS continues to feed the PC during the time needed to save the work
• this feeding is provided by a battery that is always being charged while the mains network is operating accordingly
• this battery has a set up which will hold the electrical feeding somewhere between 10 and 15 minutes
• 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
• 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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