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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