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

• Physical protection • Framework for components • EM screening • Cooling • Security • Power Supply Unit (PSU) often integrated • Form factors of motherboards vary EN0129 2

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. EN0129 5

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 EN0129 6

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. EN0129 7

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 EN0129 8

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. EN0129 9

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 EN0129 11

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 EN0129 12

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 EN0129 14

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. EN0129 15

Voltage Levels

• Original PC PSU • +12V • +5V • -5V • -12V • Later PSU’s • +12V • +5V • +3.3V

• -5V • -12V EN0129 16

+12 volts

• primarily for disk drive motors • also cooling fans • legacy motherboards did not use • modern motherboards use • passed on to expansion slots EN0129 17

+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 EN0129 18

3.3 Volts

• new boards • processor • memory • AGP video cards EN0129 19

-5 Volts

• early floppy controllers • supplied to expansion slots (ISA) • being phased out EN0129 20

-12 Volts

• serial ports • only used by some circuits • current output limited • max current 1A EN0129 21

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 EN0129 22

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) EN0129 23

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 EN0129 24

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 EN0129 26