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These are the notes I took while studying for my A+ certification, hopefully they can be of some use to you.

A+ Core Hardware Fundamentals

Lesson 1: Computer Fundamentals
Lesson 2: Component Overview
Lesson 3: System Power
Lesson 4: Motherboard
Lesson 5: Installation & Configuration
Lesson 6: Disk Drives
Lesson 7: Peripherals
Lesson 8: System Upgrades
Lesson 9: Networking
Lesson 10: Preventive Maintenance
Lesson 11: Troubleshooting

Lesson 1: Computer Fundamentals
-First computer completed in 1942

ENIAC
-Electronic Numerical Integrator and Computer
-Classified military project completed in 1945

PERSONAL COMPUTER STANDARDS
- No standards before 1981

Open Standards
-Published standards that are not copyright
-First IBM PC was released with Open Standards

IBM defined the following standards in 1981
-Data and address bus
-System and memory addressing
-Peripheral, port and adapter addressing
-System resource allocation use

Original IBM PC
-Released August 1981
-Intel 8088 processor @ 4.77MHz
-16KB memory
-Dos 1.0
-8088 was 8-bit external & 16bit internal

IBM PC-XT
-Released in March 1983
- Intel 8088 processor @ 4.77MHz
-XT stands for ‘Extended Technology’
-10MB Hard Drive
-original standards changed with this PC release

IBM PC-AT
-Released August 1984
-AT stands for ‘Advanced Technology
-Intel 80286 processor
-True 16-bit

Macintosh
-Released January 1984
-Motorola 6800 CPU
-GUI Graphical User Interface with Mouse & Desktop

Bus Standards
- A bus is any data communications path that moves data between devices

Bus qualities
-Width: measured in bits eg: 16, 32, 64bits
-Speed: measured in megahertz MHz or gigahertz GHz

Internal Bus Standards
ISA -Industry Standard Architecture
-16-bit
-first adopted by IBM
EISA -Extended ISA
-32-bit
-commonly known as ISA
PCI -Peripheral Componenet Interconnect
-32-bit
-also supports 64-bit

Types of Personal Computers
Desktop Computer
-categorised by type of case used
Desktop Case Types
Tower
-also known as full-tower
-tallest and largest type
-designed to sit on floor but can be placed on desktop
Mini Tower
-smaller version of tower case
Desktop
-designed to be placed on desktop
Low Profile
-smaller than all other types

Desktop Components
Chassis
-metal frame that holds and acts as a ground for all components
Front Cover
-plastic cover with openings for peripherals
-must be aligned properly to avoid contamination & heat dissipation problems
Slots
-hold expansion cards
Slot Cover
-covers slots normally occupied by expansion cards
-must be properly screwed into place to avoid contamination & heat dissipation problems
Bays
-areas in the chassis for holding drives
Eurocard Industry Standard
-measurement system for rack mounted server cases
-basic unit is the “u”
1u=1.75 inches (4.45cm)
2u=3.5 inches (8.9cm)
3u=5.25 inches (13.35cm)
7u=12.25 inches (31.15cm)

Laptop/Notebook Computer
-all in one system
-can attach separate keyboard mouse and monitor to use as a desktop
-ports are often covered
-a docking station can be used to have access to standard desktop ports and features

Personal Digital Assistant (PDA)
-also called Handheld or Palmtop
-touch sensitive screen
-palmtops typically include small keyboard
-usually have docking station/cradle

PC Block Diagram
-Processing à Storage à Input/Output

Input and Output (I/O) devices
-input devices include keyboard, mouse, scanner, bar code reader, monitors (touch screens)
-output devices include monitor, printer, plotter

Combined I/O devices
-send and receive data
-e.g. modes, network interface cards (NICs)

Troubleshooting a touch screen
-make sure screen is clean
-use proper tool for entering information. Incorrect tool can garble data or damage screen
-isolate problem to screen or pen
-make sure pens light is properly attached
-make sure pen light is sufficiently bright
-make sure pen cable is not worn or damaged
-restart application or computer

I/O Controller
-all I/O devices communicate via I/O controller
-either on motherboard or separate I/O card
-malfunctioning I/O devices often due to faulty I/O controller

Storage
-volatile short-term storage
-nonvolatile long-term storage

Virtual Memory
-used when PC runs out of physical RAM
-called a swap file: PC moves programs and data to and from swap file as necessary

Combined Input, Output and Storage devices
-e.g. digital video camera

Software
-differentiated between Operating System and Application software
Operating System (OS) Software
-controls hardware resources
-provides a user interface
-provides an environment for running applications
-includes device drivers
Application Software
-everything thing else that does not falling into OS category
-MS Windows can blur the line between OS and Application with Notepad and Internet Explorer which are bundled with the OS, although they are still application software

Hardware
-everything you can physically see and touch
-includes peripherals

Firmware
-somewhere between hardware and software
-consists of a microchip that contains software
-nonvolatile software storage
-e.g. BIOS
-peripherals and expansion cards often have firmware

Field Replacable Unit (FRU)
-computer element that can be replaced without sending back to manufacturer
-servers often have database of FRU elements
-notebooks have very limited FRU list

Opening Systems
-turn off
-unplug
-ensure you are static free by touching large metal object or using wrist strap
-ensure nothing can fall into system
-study how case opens

Hot Swapping
-replacing components while system is on
-often possible with high end servers
-includes power supplies, hard drives, RAM, PCI cards
-usually requires software or hardware switches to power off device before replacement
-desktops do not include hot swappable components

Numbering systems
-decimal (base 10)
-binary (base 2)
-hexadecimal (base 16)

Binary Numbering
-based on powers of 2
-1 and 0
-read binary values from right to left

Power	Decimal	Binary
2^0	1	1
2^1	2	10
2^2	4	100
2^3	8	1000
2^4	16	10000
2^5	32	100000
2^6	64	1000000
2^7	128	10000000
2^8	256	100000000

Converting binary to decimal
e.g. 101 in binary = 5 in decimal
This is calculated by adding:
1×2 0=1
0×2 1=0
1×2 2=4
Total=5

Hexadecimal Numbering
-uses digits 0 to 9 and letters A to F
-each hexadecimal digit represents the value of a 4 digit binary number
-hex numbers are often written with a “h” following the number to prevent confusion with decimal numbers. Eg 0060h

Decimal Hex Binary
0 0 0000
1 1 0001
2 2 0010
3 3 0011
4 4 0100
5 5 0101
6 6 0110
7 7 0111
8 8 1000
9 9 1001
10 A 1010
11 B 1011
12 C 1100
13 D 1101
14 E 1110
15 F 1111
16 10 10000
17 11 10001
18 12 10010
19 13 10011
20 14 10100
…
50 32 110010
100 64 1100100
1000 3E8 1111101000

Converting Hex into Binary and Decimal
-first convert each hex value into binary then decimal
e.g. 3DC in hex is:
Hex Value Binary Value
3 0011
D 1101
C 1100
So the binary equivalent of 3DCh is:
001111011100
And the decimal equivalent is:
4+8+16+64+128+256+512=988

Converting Binary into Hex
-group the binary numbers into groups of 4 then convert to decimal then convert to hex
-group from right to left!
-the last group of 4 binaries may not have 4 digits!

Bits and Bytes
Bit
-Binary Digit representing either 1 or 0
Byte
-A group of 8 bits
-can represent decimal values from 0 to 255
Word
-amount of data a processor can handle. Usually 16bits or 2 bytes

Storage Values
Unit Description
byte 8 bits
kilobyte(KB) 1024 bytes
megabyte(MB) 1024 KB or 1,048,576 bytes
gigabyte(GB) 1024 MB or 1,073,741,824 bytes
Unit Description
bit a single binary digit
nibble 4 bits
kilobit(Kb) 1024 bits
megabit(Mb) 1024 kilobits
gigabit(Gb) 1024 megabits

Note: computers consider 1024 to be a thousand

American Standard Code for Information Exchange (ASCII)
-standard code for storing text
-original ASCII was 7-bit defining 128 values
-latest ASCII is 8-bit defining 256 values

Unicode
-16-bit international standard defining 65,536 characters

Serial Communication
-one bit at a time over a single line
-Serial/com port max speed is 115Kbps or 14.4KBps

Parallel Communication
-moves several bits at a time
-requires a separate line for each bit
-also requires control line(s) to manage data transfer
-PC parallel ports (LPT) are 8-bit
-LPT stands for Local Printer Terminal
-originally 500Kbps but now faster

Asynchronous Communication
-communication can occur at any time
-bits move at a standard rate but the delay between groups of bits is variable
-start and stop bits identify beginning and end of data stream

Synchronous Communication
-uses a timing signal to keep conversation synchronized
-start and stop bits not required
-more efficient that asynchronous but more difficult to implement

Lesson 2: Component Overview
Motherboard

Pin Headers
-pins on a motherboard that IDE & floppy drive ribbon cables connect to

CPU
-Executes program steps and manipulates data
-transfers data between system memory and devices, except DMA devices which access memory directly
-most critical factor in determining system performance
-CPU’s used to be permanently socket-mounted to motherboard but are now considered FRU’s
-laptop CPU’s are not FRU’s

Memory
-used for temporary program and data storage
-another important factor in determining system performance
-mounted in small circuit boards as either SIMMs or DIMMs

CMOS
-low power static RAM
-stores system configuration information including number and type of hard drives, enabled or disabled system ports etc.
-entering CMOS is done at boot time by pressing either F2, delete or F10 key although this can very. The correct key is usually reported during POST

Magnetic Media
-data is stored as changes in magnetic field, referred to as magnetic flux changes

Optical Storage
-read dark areas called pits on a reflective background
-writable CD-ROM and DVD store data by emulating pits by creating dark areas in a dye that covers the disc substrate
-more stable over time than magnetic media
-perfect for software distribution

Floppy Disk Drives
-uses a flexible plastic platter covered with magnetic medium
-has two read/write heads attached to single actuator arm that moves across the disks surface
-5.25-inch floppies are rare but 3.25-inch floppies persist in today’s PC’s

Tape Drives
-often seen with network servers
-use a data cartridge that contains a thin ribbon of Mylar plastic or similar material covered with a magnetic medium
-data is written or read from the magnetic medium as the tape moves across a fixed read/write head
-read/write head referred to as fixed but can usually move vertically allowing multiple data tracks on a single tape increasing storage capacity
-symptoms of problems that can lead to data loss include faded tape, worn tape with streaks, noisy mechanisms.

Keyboard
-most have 102 or 104 keys
-some have additional keys for Internet navigation etc
-laptops have fewer keys but compensate with multi functions keys

Mouse
-called pointing device
-have two buttons called left and right buttons but more accurately referred to as button 1 and button 2
-types of pointing devices include optical mouse, trackball, touchpad, drawing pad, joystick, touch-screen

Display Monitors
CRT
-cathode ray tube much like a television
-screen coated with phosphors that glow when struck by electrons emitted by electron gun
-electrons fired by electron guns at rear to tube

LCD
-uses liquid crystal diode
-voltage is applied to each liquid crystal diode to cause it to darken
-polarised filters generate colours
-also called flat panel displays

Monitor Properties
-viewable size is how much visible screen can actually be used to display data
-resolution refers to maximum number of picture elements (pixels) that can be displayed without distortion
-dot pitch is the distance between two dots of the same colour

Printer
-an output device
-generates hard copy
-printer types include dot matrix, ink-jet & laser
-can be attached to PC via USB, parallel, network, IEEE 1394, infrared, serial, SCSI

AC Adapters
-unique to portable systems
-converts AC line voltage into DC voltage

Boot/Startup Process
-boot process occurs when power is applied to a system, CTRL-ALT-DEL is pressed in DOS based sessions, or a restart command is run from the OS environment
-startup initiated by applying power is called Cold Boot
-startup initiated by CTRL-ALT-DEL or restart command called Warm Boot
-some components not fully initialized during warm boot, but all are tested

POST Process
-begins by testing motherboard devices including processor, memory, CMOS memory and BIOS itself
-errors expressed as series of beeps
-if successful POST then detects and tests video adapter, then keyboard, hard drives, optical drives, floppy drives, and expansion slots
-if no fatal errors detected POST attempts to locate master boot record (MBR)
-the order in which POST searches for MBR is called boot priority which is stored in CMOS

Lesson 3: System Power
Power Supply
-converts AC line voltage to DC voltages

Power Terms
Electricity
-a form of energy; charged atomic particles called electrons
Conductor
-a material such as copper or silver that can provide a path for electrons to flow
Insulator
-a material such as rubber or glass that does not provide a path for electrons to flow
Resistance [Ohm (Ω)]
-the measurement of how much a material impedes the flow of electrons
Circuit
-a complete path through which electrons can flow
Voltage [Volt(v)]
-measurement of electromotive force
-physically voltage is an excess of electrons waiting to flow to an area with a deficiency of electrons
Current [Ampere (a)]
-the measurement of electron flow through a conductor
Power [Watt(w)]
-The measurement of the work performed by an electric current
Ground
-the reference point from which voltage is measured
Ohms Law
-V=IR
-i.e. voltages is a function of current X resistance

Power Supply Block Diagram
-consists of switching network, transformer & voltage regulator

Switching Network
-provides a level of line conditioning to eliminate spikes and sags
-maintains constant frequency
-converts AC sine wave into square wave

PC Transformer
-steps down input voltage
-generates 5v and 12v output voltages
-power is still AC voltage

Regulator
-converts AC from transformer to DC
-square wave voltages converted into steady DC voltage

Feedback Circuit
-allows switching network to compensate for changes in the amount of current required by the computer

Multimeter
-used to test AC voltage, DC voltage, continuity, resistance, current
Measuring DC voltages
-touch black lead to black ground wire
-touch red lead to wire you want to test

AT Form Factor Power Supplies
-has two 6-pin connectors labeled P8 & P9 or P1 & P2
-connectors are keyed to ensure correct orientation

AT Motherboard P8/P9 pin-outs
Pin Voltage Standard Colour
P8-1 Power_Good(+5v) Orange
P8-2 +5v Red
P8-3 +12v Yellow
P8-4 -12v Blue
P8-5 Ground (0v) Black
P8-6 Ground (0v) Black
P9-1 Ground (0v) Black
P9-2 Ground (0v) Black
P9-3 -5v White
P9-4 +5v Red
P9-5 +5v Red
P9-6 +5v Red

ATX Form Factor Power Supplies
-20 pin connector
-connector is keyed to ensure correct orientation
-has molex connector for optical and hard drives
-mini connector for floppy drives

ATX Motherboard pin-outs
Pin Voltage Standard Colour
1 +3.3v Orange
2 +3.3v Orange
3 Ground(0v) Black
4 +5v Red
5 Ground(0v) Black
6 +5v Red
7 Ground(0v) Black
8 P_Good(5v) Grey
9 +5v standby Purple
10 +12v Yellow
11 +3.3v Orange
12 -12v Blue
13 Ground(0v) Black
14 PS_On Green
15 Ground(0v) Black
16 Ground(0v) Black
17 Ground(0v) Black
18 -5v White
19 +5v Red
20 +5v Red

Disk Drive (molex) connector pin-outs
Pin Voltage Standard Colour
1 +12v Yellow
2 Ground(0v) Black
3 Ground(0v) Black
4 +5v Red

12v Tolerances
-acceptable 12v range is 11v-13v (i.e. +/-1v)

Notebook Battery Types
Nickel Cadmium (Ni-Cad)
-original batteries for notebooks
-suffer from ‘memory effect’ when partially charged and recharged
-recharge can take up to 24hours
Nickel Metal-Hydride (Ni-MH)
-longer operating time than Ni-Cad
-recharge takes 2-3 hours
Lithium-ion (Li-ion)
-longer operating time than Ni-Cad
-recharge takes 4-5 hours
Fuel Cell
-alternative to electrical storage
-uses fuel tank & electronic equipment
-various fuels including hydrogen and methanol converted into energy
-10+ hour life span
-no memory effect
-not as convenient as Li-ion

Troubleshooting Power Supplies

Signs of power supply failure
-spontaneous reboots
-system will not power on at all

Dirty Power Supplies
-spikes, sags and variations in frequency
-problems can be caused by other users on the same power supply line

Surge Suppressor/Protector
-protect from short term over voltage by absorbing the spike and shunting to ground
-power strips often have surge protectors
-it is hard to know when a surge protector has failed so but one with and indicator LED

Line Conditioner
-provide clean stable power
-do not protect against power loss

Standby Power Supply (SPS)
-not designed for PC’s
-switching time is often too long and causes PCs to reboot
-e.g. a diesel powered motor generator is an SPS

Uninterruptible Power Supply (UPS)
-best all round protection device
-uses a battery connected to AC line voltage
-switching time is instantaneous which is ideal for PCs
-UPS can initiate system shutdown if power not restored eliminating data loss
-also provides line conditioning
-make sure UPS provides enough power for your system
-never plug a laser printer into a UPS as they have large power requirements that can damage the printer

Testing a UPS
-make sure it is plugged in and charging
-use proprietary UPS management software to ensure UPS is active
-unplug UPS from AC voltage to ensure it properly activates
-verify that UPS sends a warning before losing batter power
-a UPS will only provide power for about 30mins

Electromagnetic Interference (EMI)
-electric noise
-emitted by fluorescent lights, electric motors, power lines, switches and relays
-best way to avoid EMI is to route cables away from EMI sources
-alternate way to avoid EMI is to use shielded cable

Electrostatic Discharge (ESD)
-the most hazardous form of EMI
-caused when a build-up of charge is transferred from one object to another

Minimising ESD
-easiest way is to touch a large metal object before working on ESD sensitive equipment
-or use a grounded static wrist strap
-spray working areas (especially carpets) with anti-static spray
-not removing components from protective containers until ready for installation
-must remove grounding strap before working on high voltage devices eg power supplies and monitors

Safety Concerns
-when a person touches live voltage, muscle contractions can make it impossible to pull free
-unplug the device if possible or use a leather belt to pull the person free
-when working with a high voltage device only use one hand if possible

Lesson 4: Motherboard
Motherboard Form Factors
-”form factor” refers to motherboard design and layout
-3 form factors: AT, ATX and NLX
-also have mini versions
-ATX and NLX have standard ports installed directly on motherboard

AT Motherboard
-based on IBM AT motherboard
-12×13inch PCB but also 12×13.5 and 12×13.8
-mini-AT is 8.66×13 inch PCB

ATX Motherboard
-12×9.6inch PCB
-de facto standard released as specification 2.0 in December 1996
-similar to mini-AT but rotated 90 degrees allowing full length adapter cards
-side mounted cooling fan can cool processor and peripheral cards
-power connector is closer to CPU than other form factors
-less expensive to manufacture
-supports both 5v and 3.3v
-has fewer integrated circuits than AT

Mini ATX
-11.2×8 inch PCB
-higher density chipsets used to reduce size

Communication Network Riser (CNR)
-communicates in serial
-supports NIC or modem
-frees up PCI slot
-tied to south bridge

Audio Modem Riser (AMR)
-standard developed by Intel
-supports audio features in modems
-frees a PCI slot

Mobile Daughter Card (MDC)
-same as AMR but designed for notebooks

NLX Motherboard
-introduced September 1996
-uses motherboard and riser combination
-only expansion slot is AGP
-all expansion slots on riser card
-connects to motherboard through 340pin edge connector
-PCB size varies

Northbridge
-memory controller for processor including L2 cache
-works with PCI and AGP controllers (i.e. more than one chip)

Southbridge
-sits on Northbridge bus
-provides i/o functions for ISA, IDE, AGP & serial
-one discreet chip
-can be compatible with many different Northbridge chipsets

Microprocessors
I/O Unit
-responsible for passing data and instructions into and out of processor
-link between processor and rest of computer including address bus and data bus
-address bus specifies a location in memory
-data bus is the path over which executable instructions and data move into and out of processor

Control Unit
-controls execution of instructions in the processor
-receives instructions from the I/O unit, translates if needed and passes to arithmetic/logic unit
-keeps track of which instruction within a program is currently being executed

Arithmetic/Logic Unit and Floating Point Unit
-performs all logic functions and mathematical calculations
-receives instructions from I/O unit and executes each instruction

Math Coprocessor (floating point unit)
-provides faster processing for involved calculations
-FPU is now integrated into processor

Processor Cache
-high speed memory built into processor
-first introduced with Intel 80386 processor

L1 Cache
-primary cache located on processor itself
-early processors used write through cache which could be used for reads only (i.e. data going into processor)
-Pentium introduced write back cache which supports both reads and writes

L2 Cache
-secondary external cache
-Pentium systems located L2 cache in system memory
-Pentium pro moved L2 cache onto processor
-loaded with instructions and data that the processor might need

Symmetric Multipricessing (SMP)
-the use of 2 or more CPU’s in a system
-both operating system and BIOS must support SMP

Processor Modes
-when a processor is first initialized it is running in real mode
-an 8088 processor runs in real mode which is limited to 1MB memory and 16-bit instructions
-Win95/98 start with processor in real mode then switch to protected mode during OS startup

Protected Mode
-name comes from protection implemented to stop programs overwriting memory assigned to each other

Virtual Real Mode
-emulation of real mode when running a 32-bit OS in protected mode
-also called virtual 8088 processor

Processor Generations
Gen Description
1st 8086(`78), 8088, 80186, 80188
2nd 80286(`82) IBM PC AT
3rd 80386(`85) true 32-bit
4th 80486 (introduced 1989)
5th Pentium (`93)WB cache Sock 7
6th Pent Pro, PII, AMD K6. L2 cache
7th PIII, Xeon, AMD Athlon
8th Pentium 4 and Athlon

Pentium Charcteristics
-Complex Instruction Set Computer (CISC)
-16KB(program)/16KB(data) L1 cache
-all Pentium processors have FPU
-Pentium MMX and on have additional multimedia extensions
-MMX defines 57 additional graphics and sound instructions
-SSE/SIMD (Streaming Single Instruction Multiple Data Extensions) defines 70 instructions additional to MMX with Pentium III
-first Pentium was nearly equal to two 80486 processors

1stGen 2nd Gen MMX Pent
Sock 273pin 296pin
Voltage 5v 3.465/3.3 2.8v
Multiplier 1x 1.5x - 3x 1.5 - 4.5x
Speed 60-66MHz 75-200MHz 60-266MHz
Registers 32-bit 32-bit 32-bit
Ex. Data Bus 64-Bit 64-Bit 64-Bit
Address Bus 32-bit 32-bit 32-bit
Transistors 3.1M 3.1M 4.5m

Pentium Pro
-387-pin socket mounted.
-3.1 or 3.3v
-8KB(program)/8KB(data) L1 cache
-256, 512 and 1MB L2 cache

Pentium II
-slot mounted single edge contact cartridge (SECC & SECC2)
-16KB(program)/16KB(data) L1 cache
-512KB L2 cache
-7.5M transistors

Celeron
-basically same as PII with no 128KB cache
-128KB Celeron called CeleronA
-single edge processor package (SEPP).
-Like SECC without cover
-has 32-bit address bus which means it is limited to 4GB memory instead of 36-bit address bus which has 64GB max.
Pentium III
-introduced SIMD extensions
-uses SECC2 packaging

Xeon
-high end versions of Pentium 3 & 4
-larger and faster L2 caches

Pentium 4
-improved pipeline
-socket 423 and 478
-uses special power supply

AMD Processors
K5
-Reduced Instruction Set Processor (RISC)
-supports less instructions but can process them faster
-has instruction decoder that translates Intel instructions into RISC
-16KB program/8KB data cache
K6
-licensed and implemented MMX before Intel
-socket 7
-original K6 equivalent to Pentium 200
-has two separate 32KB L1 program/data caches making it possible to read & write data at same time(write back cache)
-K6-2 has additional instructions in addition to MMX
-K6-2 equivalent to Pentium 350
-K6-3 competitor to PIII
Duron
Athlon/K7
Athlon64/K8
-64bit
Cyrix Processors

Cooling the CPU
Heat Sink
-passive device
Fan
-active device
Liquid Cooling Units
-active device
-uses radiator to cool water that is passed over the CPU core

Memory
RAM
-Random Access Memory
-volatile storage used for temporary data storage
ROM
-Read Only Memory
-non-volatile storage e.g. BIOS
-types include ROM, PROM, EPROM, EEPROM
Parity RAM
-used to check whether data has been lost or written over when data is moved
-uses 9bits instead of 8
-when parity is found to be incorrect, an error is reported
Error Correction Code (ECC) RAM
-detects and automatically corrects errors
Ram Types
Static RAM (SRAM)
-retains contents as long as power applied to memory chips
-e.g. CMOS
Dynamic RAM (DRAM)
-each dynamic memory cell(each bit) is like a capacitor
-capacitors can hold charge for a short time (a millisecond) before it needs to be refreshed
Fast Page Mode DRAM (FPM DRAM)
Extend Data Output DRAM (EDO DRAM)
Synchronous DRAM (SDRAM)
-data input and output are synchronised with external clock
-designed with two internal banks
-as one bank is accessed, the other is preparing to be accessed
Video RAM (VRAM)
-used for video adapters
-dual ported
-as one port is used to write, the other is used to refresh monitor display
Windows RAM (WRAM)
-nothing to do with Microsoft
-high performance VRAM
Synchronous Graphics RAM (SGRAM)
-can be synchronised with system bus up to 200MHz
Multibank DRAM (MDRAM)
Double Data Rate RAM (DDR RAM)
-184 pins
-a CPU has two clock transitions: the rising edge and falling edge
-combined they are a clock cycle
-DDR is able to transfer data at both transitions of the cycle
Rambus DRAM (RDRAM)

Single Inline Memory Module (SIMM)
-8bit 30 pin SIMMs installed in banks of 4 with 32bit processors
-72pin SIMMs support 32bit data path and can be installed as single chip
-only has pins on one side of chip ?
Dual Inline Memory Module (DIMM)
-32bit 72pin SIMMS must be installed in pairs to support 64bit data path Pentiums
-144pin and 168pin DIMMs support 64bit data path
-168pin DIMMs support ECC
Small Outline DIMMs (SODIMM)
-used in notebooks
-72pin 32bit data path
-144pin 64bit data path
Micro DIMM
-100, 144 and 172pin
Rambus Inline Memory Module (RIMM)
-form factor for Rambus chips
-184 pins
Rambus Continuity Module (RCM)
-empty slots must be filled with RCM`s
-form factor for notebook Rambus chips is called ?

Lesson 5: Installation & Configuration
System Resources
-Interrupt Request (IRQ)
-I/O Address
-Direct Memory Access (DMA)
-ROM BIOS
-PC communication is controlled by interrupts
-PC-XT supported 8 interrupts numbered 0-7
-PC-AT added 8 additional IRQs numbered 8-15
-interrupts originally controlled by 8259 interrupt controllers
-system timer IRQ 0 has highest priority

Standard IRQ Assignments

IRQ	Priority	Standard Assignment
0*	1	System Timer
1*	2	Keyboard Controller
2	Reserved	Cascades IRQ’s 8-15
3	11	COM2 COM4
4	12	COM1 COM3
5	13	LPT2
6*	14	Floppy Disk Controller
7	15	LPT1
8*	3	Real-Time Clock (RTC)
9	4	Substitute for IRQ 2
10	5	Unassigned
11	6	Unassigned
12	7	P/S2 Mouse
13	8	Math Coprocessor
14*	9	Primary IDE
15	10	Secondary IDE

*=fixed IRQ assignments that cannot be changed
-as a general rule if no device is assigned to an IRQ the IRQ is available for assignment
-anything assigned to IRQ2 is assigned IRQ9, so you can assign IRQ2 or IRQ9 to any device but not both
-SCSI adapters usually IRQ 11
-USB controller usually IRQ 11 (or IRQ 10 if SCSI present)

I/O Address
-I/O address is a memory location
-when processor needs to send command or data to a device, it writes the value to the devices I/O address. Processor then activates device’s IRQ line causing the device to read and process contents of addressed memory
-when device wants to communicate with processor, it writes data or status info to its I/O address, then activates its IRQ line. Processor will then read contents of device’s I/O address when it services the interrupt.

Standard I/O Address Assignments in Hexadecimal
Device I/O Address Range
Keyboard-PS/2 Mouse 0060 or 0064
Real-Time Clock 0070 - 0071
Math Coprocessor 00F0 - 00FF
Primary IDE 01F0 - 01F7
Secondary IDE 0170 - 0178
Game Adapter 0200 - 020F
LPT1 0378 - 037F
LPT2 0278 - 027F
COM1 03F8 - 03FF
COM2 02F8 - 02FF
COM3 03E8 - 03EF
COM4 02E8 - 02EF
Mono Display Adapter 03B0 - 03BF
EGA display adapter 03C0 - 03CF
CGA display adapter 03D0 - 03DF
VGA display adapter 03C0 - 03DA
XT disk controller 0320 - 032F
Floppy Disk Controller 0370 - 0377

-display adapter assignments overlap
-keyboard and PS/2 mouse share an I/O address
-330h - 331h is default i/o for midi port on many sound cards

Programmed input/output (PIO)
-requires all data first pass through the processor
-considered outdated in favor of DMA

Direct Memory Access (DMA)
-devices directly address bypassing processor
-originally controlled by DMA chip but now integrated
-a device that does not support DMA must move data through its i/o address
-original PC & XT supported DMA channels 0,1,2,3
-PC-AT increased to 8 DMA channels 0-7
-DMA channel 2 assigned to floppy disk controller
-DMA channel 4 is assigned as the cascade from the second DMA controller to the first
-SCSI adapters default to DMA 6
-sound cards typically use DMA0 or 1 or both

Ultra-DMA (UDMA/UltraATA)
-uses strobe technology in which a single command contains both data and command signal
-addition of Cyclical Redundancy Check (CRC) which reduces errors
-uses new 40 pin cable which has a blue connector at one end
-new cable increases EMI shielding

Latest UDMA Standards
-UDMA/ATA-66 up to 66MBps
-UDMA/ATA-100 up to 100MBps
-UDMA/ATA-133 up to 133MBps

ROM BIOS
-system memory between 0A0000h-0FFFFFh (640KB to 1024KB) is reserved for system use including for ROM BIOS from 0C0000h
-an adapters bios is physically on the adapter board, but it must be mapped to a memory area between 0C0000h-0FB999h. This allows the adapters bios to be addressable by the system
-each adapter board must be assigned a unique non overlapping ROM BIOS address range

Memory Addresses Typically Available for Assignment to ROM BIOS
-0D0000, 0D8000, 0E0000, 0E8000, 0F0000, 0F4000, 0F8000

Viewing and Changing Resource Assignments

Windows 9x/Me
-Start | Settings | Control Panel | System Icon | Device Manager Tab
-Right click My Computer | Properties for system resources which can be displayed by IRQ, I/O, DMA and memory usage

Windows NT
-Start | Programs | Administrative Tools | Computer Management | NT Diagnostics icon

Windows 2000
-Start | Settings | Control Panel | Administrative Tools | Computer Management | Device Manager
-for summary resource lists expand System Information | Hardware Resources

Windows XP
-Start | Settings | Control Panel | System | Hardware tab | Device Manager button.

Burst Mode
-allows device to take over temporary control of processor’s external data bus

Bus Mastering
-allows devices to directly communicate with one another bypassing CPU

Bus Summary
Bus Name Data Width Memory Clock Speed
(bits) (MHz)
ISA 16 16MB 8.33
EISA 32 4GB 8.33
MCA 16/32 16MB/4GB 10
VL-bus 32 4GB 33
PCI 32/64 4GB 33
AGP 32 4GB 66
PCMCIA 16 64MB 8

Industry Standard Architecture
-ISA is NOT a local bus
-16bit bus introduced with PC-AT
-has two slots. 8bit slot with 62 connectors and 16bit slot with 36 connectors
-8bit ISA boards will not work in 16bit slots as they are designed to run at 4.77MHz

Extended ISA (EISA)
-32bit
-additional connectors between and below ISA connectors
-longer slot has 124 connectors, shorter slot has 74 connectors
-very limited acceptance

Micro Channel Architecture (MCA)
-IBM’s attempt at proprietary 32bit bus
-introduced with IBM Personal System 2 (PS/2)
-limited acceptance

Video Electronics Standards Association Bus (VESA-Bus)
-based on ISA with third inline 116pin slot
-backward compatible with ISA
-supports burst mode and bust mastering
-only implemented on 80386 & 80486

Accelerated Graphics Port (AGP)
-direct access to system RAM

AGP Modes
AGP Mode Base Speed Effective Clock Speed
(MHz) (MHz)
1x 66 66
2x 66 133
4x 66 266
8x(AGP3.0) 275 512
-AGP slots are only found on PII systems and higher

Peripheral Component Interconnect (PCI)
-supports burst mode and bus mastering
-124pin connector
-introduced 4 additional interrupts
-PCI adapters share system IRQ assignments
-full plug and play
-32bit up to 133Mbps

64bit PCI
-64bit at 66MHz up to 266Mbps
-backwards compatible with 32bit PCI as long as PCI driver supports 32bit

Personal Computer Memory Card Industry Association (PCMCIA)
-credit card sized 68pin connector
-hot swappable
-2.12 x 3.37 inch form factor

PCMCIA Card Types

PCMCIA Type	Description	Slot Notes
Type I	3.3mm thick	Slot supports Type I only
Type II	5mm thick	Slot supports Type I & II
Type III	10.5mm	Slot supports Type I, II & III

Computer Aided Design (CAD)
-use of computers to create a design for a product
Computer Aided Manufacture (CAM)
-use of a computer to help manufacture a product
Scale Up
-upgrading systems to accommodate demand
Scale Out
-obtain new systems to accommodate demand

Lesson 6: Disk Drives
Track
-information stored in concentric circles

Platter
-flat circular object covered with magnetic substance
-older platters made of aluminum, newer are made of ceramic or glass

Cylinder
-cross section of a single track through all platters
-both top and bottom of platter

Sector/Segment
-a small piece of a track that looks like a pie
-smallest unit of measurement (512bytes)
-each track has same number of sectors
-sectors near the spindle are physically smaller

Cluster
-a group of sectors on a single track
-most OS’s write information in clusters
-smallest amount of disk space that can be assigned for data storage

Density
-number of tracks stored per inch TPI (Tracks Per Inch)

Floppy Disk Drive
-first floppy drives were 9inch with 250KB data
-first floppy drives used in PCs were 5.25inch with 180KB data
-has moveable arm with opposable heads
-stepper motor moves arm across disk surface

3.5inch Floppy Disks
-invented by Apple
-34 pin cable with mini power connector
-when connected to end of cable will be A: drive
-twist in pins 10 to 16 near end of cable are for drive and motor select signals for A and B drive
-red stripe on cable will usually go to pin 1
-double Density 720KB (double sided)
-high density 1.44MB (double sided)
-extra high density 2.88MB (double sided)
-when write protection notch is open disk is read write
-susceptible to magnetic fields and heat

Hard Disk Drive Fundamentals

ST506/412
-developd by Seagate in 1978, improved to ST412 in 1981 and included in PC-AT
-practical limit of 200MB and 1.2Mbps
-phased out around 1989

Enhanced Small Devices Interface (ESDI)
-developed by Maxtor in 1983 and adopted by ANSI
-limit of 1GB and 24MBps
-up to 7 devices per controller
-phased out around 1991

Advanced Technology Attachment: Integrated Drive Electronics (ATA: IDE)
-developed by Compaq, Western Digital, Conner in 1988 and accepted by ANSI under name ATA
-based on 16bit ISA
-two drives per controller
-limited to 504MB and 12MBps at 5V

Interleave
-sets order in which sectors are read from and written to a track
-compensates for slow bus speeds

Write Pre-compensation
-compensation method used on older drives to improve read/write reliability on inner sectors

Enhanced Integrated Drive Electronics (EIDE/ATA2)
-released 1996
-up to 137.4GB
-support for PCMCIA
-recent modifications added support for advanced power management and IEEE1394

Logical Block Addressing (LBA)
-developed by Western Digital
-28bit addressing system allowing PC to reference an area of the hard disk by unique sector number rather than CHS value i.e. uses logical values to represent drives geometry
-called geometry/sector translation to give Logical Geometry
-allows BIOS to address up to 8.46 GB

Int 13h Extensions
-allows system to completely ignore how BIOS accesses CHS
-does not translate CHS into logical geometry
-up to 137.4GB

AT Attachment Packet Interface(ATAPI)
-allows EIDE controller to support CDROM droves

Cable Select
-uses specially designated CSEL cable
-drive must be EIDE and support CSEL (not supported by IDE)
-BIOS must support CSEL

Serial ATA (SATA)
-drives communicate via 250millivolt DC signal
-3.3v 15pin power cable
-7 (or 9?) pin data cable

SCSI
-early forms of SCSI date to 70s
-first recognizable version in 1986 by Apple
-allows daisy chaining including mix of internal/external
-supports bus mastering

SCSI-1 (Narrow/8bit)
-ANSI in 1986
-8bit data bus at 5 MBps
-7 devices
-50 pin cable known as B cable
-6M for SE signaling
-25M for HVD signaling
-12M for LVD

SCSI-2 (Narrow/8bit & Wide/16bit)
-ANSI in 1994
-backward compatible
-5MBps over 8bit data bus
-50pin cable
-same cable lengths as SCSI-1
-optional support for fast SCSI up to 10MBps

Wide SCSI(16bit)
-came with SCSI-2 standard
-16bit data bus
-68pin cable known as P cable
-15 devices
-LVD cable length 3M
-HVD cable length 25M

Fast Wide SCSI
-20MBps

SCSI-3/Ultra SCSI
-ANSI in 1995
-8 bit/50pin(b) cable
-16 bit/68pin(p) cable
-same time as LVD signaling
-includes Ultra/fast-20 SCSI, Ultra2/fast-40 SCSI, Ultra3/fast-80 SCSI
-each can be implemented with 8bit 50pin cable(B) or 16bit 68pin(P)

Version	Narrrow (8bit)	Wide (16bit)	Cable Limit
Ultra	20MBps	40MBps	1.5 at SE 25 at HVD
Ultra2	40MBps	80MBps	12 at SE 25 at LVD 8 at HVD
Ultra3	80MBps	160MBps	12 at LVD 16 at HVD

SCSI Signaling
Single Ended Signaling (SE)
-signal carried on one wire and other acts as ground (unbalanced signaling)
-Used with SCSI-1 & 2
-susceptible to noise
-max cable length inversely related to clock speed
6M at 5MHz
3M at 10MHz
1.5M at 20MHz

High Voltage Differential (HVD)
-two signal wires but both carry data
-one wire positive other is negative
-less susceptible to noise
-expensive. Standard now dropped

Low Voltage Differential (LVD)
-inexpensive and can co-exist on same bus as SE signal devices
-12M cable length at any SCSI-3 bus clock rate

SCSI Termination
-scsi device chain must be terminated at the ends and only at the ends
-most devices self terminate

SCSI Termination Types
Passive
-a physical device

Active
-an electrical device built into the scsi drive
-first introduced in SCSI2

Auto
-can act as either passive or active

SCSI Priority
-Highest 7 6 5 4 3 2 1 0 15 14 13 12 11 10 9 8 Lowest
-host adapter is usually SCSI ID 7

SCSI Jumpering
-narrow SCSI has 3 jumbers
-wide SCSI has 4 jumpers numbered 0 to 3
jumper 0 has binary value of 1
jumper 1 has binary value of 2
jumper 2 has binary value of 4
jumper 3 has binary value of 8

Logical Unit Number
A logical unit number (LUN) is the numeric value that is assigned to an I/O device

Laptop Storage devices
-2.5inch internal hard disk with 44pin ribbon cable
-PCMCIA type III hard drives
-external devices via I/O ports. E.g. external USB hard drives.

CD-ROMs and CD-RWs
-audio CDs introduced in 1979
-12×0.1cm CD standard introduced by Sony & Phillips in 1982
-0.5cm hole
-CD-ROMs introduced in 1985
-CD surface consists of ‘Pits’ and ‘Land’ which is read by laser combined with timing signal
-when laser detects a transition from Pit to Land or Land to Pit this is treated as a ‘1’
-no transition is treated as a ‘0’

CD-ROM Access Speeds

DRIVE SPEED	TRANSFER RATE (BPS)	ACCESS TIME (ms)
Single-speed (1x)	153,600	400
Double-speed (2x)	307,200	300
Triple-speed (3x)	460,800	200
Quad-speed (4x)	614,400	150
Six-speed (6x)	921,600	150
Eight-speed (8x)	1,228,800	100
Ten-speed (10x)	1,536,000	100
Twelve-speed (12x)	1,843,200	100
Sixteen-speed (16x)	2,457,600	90
Eighteen-speed (18x)	2,764,800	90
Twenty-four-speed (24x)	3,686,400	90
Thirty-two-speed (32x)	4,915,200	85
One-hundred-speed (100x)	15,360,000	80

DVD (Digital Video Disc)
-initial standard of 4.7GB
-double sided discs have 9.4GB
-dual layer standard of 8.5GB

Standard	Storage Capacity	Description
DVD-R	3.95	Released 1997 Write once.
DVD-RAM	2.6 & 4.7	Released 1997 Write once.
DVD-RW	4.7	Rewritable
DVD+RW	2.8 then 4.7	Supports Mt Rainier

Tape Devices
-long history of 50 years

Tape Formats
Quarter Inch Cartridge(QIC)/Digital Audio Tape (DAT)/Digital Data Storage (DDS)
-released 1983
-capacities from 40MB to 25GB
Digital Data Storage (DDS) Standards

DDS Standard	Capacity (GB)	Capacity (GB-Compressed)
DDS-1	2	4
DDS-2	4	8
DDS-3	12	24

Digital Linear Tape (DLT)
-40 GB uncompressed
-Super DLT up to 220GB

Travan Tapes
-developed by 3M

Travan Level	Uncompressed Storage	QIC compatibility
TR-1	400 MB	QIC-80-MC
TR-2	800 MB	QIC-3010-MC
TR-3	1.6 GB	QIC-3020-MC
TR-4	4 GB	QIC-3095-MC

Lesson 7: Peripherals
Standard Ports
Serial Ports
-asynchronous
-computer communicates internally via parallel buses therefore data converted to serial via UART
-male connector at back of PC

Universal Asynchronous Receiver Transmitter (UART)
-first UART was IBM INS8250 at up to 56Kbps but unstable above 9600bps
-16450 released in IBM PC-AT at up to 115200bps
-16550 added DMA channel support
-16550A is latest with first in first out (FIFO) support

Parallel Ports/IEEE 1284 standard
-can support network communication via Parallel Line Internet Protocol (PLIP)
-created by Institute of Electrical and Electronic Engineers (IEEE)
-female connector at back of PC

IEEE 1284 Modes

Mode	Description
Compatibility Mode	Called Centronics mode. Max 150Kbps
Nibble Mode	Allows communication in “Reverse Mode” but not truly bi-directional 4bit limited to 50Kbps
Byte Mode	Called Enhanced Bi-directional port. Allows daisy chaining. Reverse Mode. 8bit
Enhanced Parallel Port (EPP)	Truly bidirectional. 500 Kbps to 2MBps.
Extended Capability Port (ECP)	Bidirectional. Supports data compression and DMA. Up to 2MBps.

USB Ports
-supports asynchronous and isochronous serial transmission
-hot swappable and supports Plug and Play
-Low speed 1.2Mbps
-Full speed 12Mbps
-High speed 480Mbps
Firewire (IEEE 1394)
-serial communication up to 400Mbps

Connectors and Cables
Serial Calbles (RS232)
-defined by Electronics Industry Association (EIA)
-uses both DB9 and DB25

Null Modem Cable
-used for making connection between two computers
-TD signal at one end connected to RD signal at other

Parallel Cables
-DB25 connector
-has 36pin Centronics connector at printer end
-68pin mini-Centronics connector also used

Keyboard
-uses Deutsche Industrie Norm (DIN) connector
-5pin DIN and 6pin Mini-DIN

Mouse
-uses DB9 and mini-DIN

Game Port
-DB15 connector
-can also be used as MIDI connector

Monitor
-DB15 connector for VGA
-female at PC end
USB
-up to 127 devices but bandwidth is limiting factor
-‘A’ connector for port connections (i.e. at PC or hub - flat)
-‘B’ Connector for device connections (square)
-four wire cable: 2 for data and 2 for power (+5v)
-cable length limited to 5M (3M on older slow devices)

IEEE 1394
-introduced by Apple
-up to 400Mbps at 4.5M with up to 63 devices daisychained
-cable same at each end
-standard uses two twisted pairs for data and two power connectors (power and ground)
-6 pin connector is standard
-4 pin connector called mini connector. Does not provide power

IEEE 1394b
-800Mbps transfer rate
-uses 1394b cable

Infrared Developers Association (IrDA) devices
-optical equivalent of RS232 serial communication
-same transfer rates of 2400 to 115200 Kbps
-requires line of sight

Network and Telephone Connectors
British Naval Conector (BNC)
-used for coaxial cable network connections
-has conductive core with wire mesh grounding shield
-must be terminated with 50 ohm resistor

RJ-11 connectors
-used with telephone/modems
-4 contacts but only 2 wires called tip and ring

RJ-45 connectors
-8 contacts all wired but only 4 used in each direction allowing bi-directional support

Attenuation
-loss of signal strength over distance

Input Devices
Keyboard
-first PC’s released with 83 keys
-IBM PC-At had 84 keys
-current standard is 101 keys
-Windows keyboard has 104keys

Pointing Device
Mouse
-ball moves against 2 sensors translated into X and Y coordinates
-has 2 or more buttons
-also have optical mice
Trackball
-effectively a mouse turned on its back
Touch Sensitive pads
-controlled by moving finger across touch sensitive pad
Joystick
-small version of game controller joystick
Touch Sensitive Screens
-screen is sensitive to touching by finger

Monitors
Monitor Terms
Dot
-individual colour element
Dot Pitch
-diagonal distance between two dots of same colour
Pixel
-picture element
-made up of several dots
Interlace
-alternating rows are refreshed on each pass
Persistence
-how long a dot will remain lit before fading
Bandwidth
-how quickly a CRTs electron gun is turned off and on
-measured in MHz

Cathode Ray Tube (CRT)
-screen coated with phosphors that generate light when excited by electrons
-colour monitor has 3 electron guns that fire electrons through deflection coils and yoke magnet
-deflection coils and yoke magnet focus electron stream to correct location
-pattern of horizontal lines known as raster
-time for one horizontal pass known as horizontal refresh rate (HRR)
-time for one vertical pass known as vertical refresh rate (VRR)

Liquid Crystal Diode (LCD)
-liquid crystal diodes sandwiched between sheets of glass create image
-sheets of polarizing material between glass and LCDs
-filters generate red, blue and green dots
Passive Matrix
-uses transistor-transistor logic(TTL) to control voltage levels
-slower to respond to image changes
Active Matrix
-thin file transistor (TFT) arrays provide better response times

Monitor Standards
Video Electronics Standards Association (VESA)
-managing body for video monitor standards
-defined video graphics array (VGA) standards

Video Power Management
-VESA has set display power management signaling (DPMS) modes standards

DPMS modes

Status Mode	Description
On	Monitor receiving signal and displaying image
Standby	Monitor not receiving signal but can recover to ON quickly
Suspend	Monitor still receiving signal but inactive. Recovery time longer.
Off	Most of monitor circuitry is off and not receiving signal. Long recovery time.

Calculating Video Ram
HR x VR x CD / 8,388,608 = Min video RAM
8,388,608 is 1MB RAM in bits

Printers
Printer Control Language (PCL)
-defines how data and commands are passed to the printer
-there are many printer control languages but one is called “Printer Control Languate” developed by HP called PCL
-PCL is now a de facto standard up to PCL6
-also PCL XL

Postscript
-another printer control language
-developed by Adobe and used by Apple and UNIX printers

Laser Printers
-photosensitive drum included as part of toner cartridge
-printer creates a raster image of print data i.e. an image made of a series of lines

Laser Print Process

Step	Description
Cleaning	Drum is scraped clean and passed over a conditioning roller
Charging	Primary corona wire generates negative charge on drum
Imaging	Laser transfers raster image to drum
Toner Transfer	Toner applied to transfer roller. The toner is attracted to positively charged areas of drum
Image Transfer	Transfer corona placed positive charge on paper that causes paper to attract toner from drum
Fusing	Paper is passed through fuser rollers to bind toner to page

Modems
-combination of the words modulator demodulator
-in 1998 V.90 standard released
-modems are asynchronous serial
-internal modems appear as addition COM port to computer

Lesson 8: System Upgrades
Resetting BIOS passwords
1-remove CMOS battery
2-remove bios chip
3-use reset jumpers on motherboard
4-flash the bios may work
Note: erasing CMOS memory can take several days after battery removal due to capacitance in CMOS circuit

Voltage Regulator Module
-controls voltages for socket mounted processors

Scale Out
-ad additional power such as second processor

Scale Up
-upgrade existing hardware such as faster processor

Handling Precautions
-keep device in antistatic bag until ready for installation
-do not touch PCB

Lesson 9: Networking
Local Area Network (LAN)
-a network is defined as a LAN as long as long as communication does not require a public carrier

Wide Area Network (WAN)
-a collection of LANs connected through public carriers
-uses a router to connect LANs
-the Internet is a worldwide WAN

Networking Models
Workgroup
-peer to peer
-no centralized computer where all computers are equal
-computers act as both client and server

Client/Server
-security is centrally controlled
-each server managed separately

Domain
-domain servers managed as group

Directory Services
-more advanced that Domain servers
-users, computers, servers treated as logical group
-no one server acts as primary controlling server
-Win2K, XP and Novell NetWare4.x supported
-more advanced directory service called Kerberos(WinXP) and e-Directory(Novell Directory Services)

OSI Model
-developed by International Standards Organisation in 1978
-a node is any device communicating on the network
-data is divided into packets before packets before transmission from one layer to another
-transmission starts at top; i.e. Application layer 7
-each layer attaches formatting and addressing information
-when packets reach physical layer of sending PC data passes across network to receiving computer
-upon reaching physical layer of receiving computer formatting and addressing information is removed as packet passes up the OSI model

OSI Layers

Layer	Description
Application Layer 7	Responsible for formatting information used in applications EG: HTTP SMTP POP3
Presentation Layer 6	Acts to translate and interpret data i.e. will convert data into a useable form. Also responsible for encryption and protocol conversion
Session Layer 5	Establishes, manages and terminates connections/sessions between nodes
Transport Layer 4	Breaks data into Datagrams Error detection and correction
Network Layer 3	Controls physical path data should take Translates logical addresses and names into physical machine addresses
Datalink Layer 2	Controls data sent to physical layer Divided into Media Access Control(MAC) and Logical Link Control(LLC)
Physical Layer 1	Establishes and maintains physical link between nodes

Institute of Electrical and Electronics Engineers (IEEE) Standards
-started project ‘802’ in Feb 1980 to define networking standards
-802.3 defines Ethernet standard
-802.11 defines wireless networks

Data Communication Fundamentals
Signaling
-refers to method used to transmit data between nodes

Full Duplex
-data transmitted in both directions at same time
-requires one path for each direction

Half Duplex
-data transmitted in both directions but not at same time

Simplex
-data transmitted in one direction only

Host Address
-identifies a single device on a network

Network Address
-allows network to be divided into subnetworks
-a subnet contains multiple host addresses

Host Names
-a “human compatible” name
-windows machine name is called a NetBIOS name
-WANs use DNS host names
-NetBIOS stands for Network Basic Input/Output System

Topologies
-a networks physical layout

Bus
-all nodes connected to central line
-only one node can communicate at a time
-data signal broadcast along entire trunk
-uses 50ohm resistor to reduce bounce

Ring
-connected in a physical ring

Star
-cables run from each node to hub

Network Access Methods
Ethernet
-defined by IEEE 802.3

Ethernet Standards

Standard	Description
10Base2	Coax 10Mbps Bus topology called thinnet
10Base5	Coax 10Mbps with DB15/AUI called thicknet
10BaseT	Twisted pair cable either UTP or STP cat 3 Star Topology Cable length 0.6 to 100M Max 1,024 devices
100BaseT	Same as 10baseT
100BaseFL

Token Ring
-defined by IEEE 802.5
-ring topology but often physically a star
-collisions should never occur
-if receiving computer not present the token will travel in endless loop
-4Mbps or 16Mbps

Communication Protocols
Transmission Control Protocol/Internet Protocol (TCP/IP)
-de facto standard
-routable
-all hosts have 32bit IP address

Standard IP Classes

Class	Address Range	Subnet Mask
A	1.0.0.0 to 126.0.0.0	255.0.0.0
B	128.0.0.0 to 191.0.0.0	255.255.0.0
C	192.0.0.0 to 223.0.0.0	255.255.255.0

Classless Interdomain Routing (CIDR) notation
-e.g. addresses from 55.66.77.88 to 55.66.88.99 with S/N of 255.255.255.0 is represented as:
55.66.77.88-55.66.88.99/24

NetBIOS Extended User Interface (NetBEUI)
-developed by IBM as enhancement to NetBIOS
-non routable

Internet Packet Exchange/Sequenced Packet Exchange (IPX/SPX)
-Based on Xerox Network System (XNS)
-routable
-supported by Microsoft via NWLink protocol

Lesson 10: Preventive Maintenance
-if you find a worn cable you should replace it before it fails
-perform basic system operation after completing preventative maintenance

Lesson 11: Troubleshooting
Troubleshooting Goals
-minimise interruption to normal business activities
-replacing a failing system often more cost effective than repair
-a problem should not be considered repaired until users have been notified of the repair; explain problem and its resolution
-keep conversation as non technical as possible

General Troubleshooting Flow
1-check for obvious physical errors
2-determine if problem is hardware or software related
3-collect and document relevant system information
4-duplicate the failure
5-isoloate the failing component
6-repair or replace failing component
7-document the resolution
9-inform the customer

Questioning Users
Open Ended Questioning
-designed to elicit more information from the user
Closed Ended Questioning
-used to determine specific details
-if closed ended questioning fails revert to open ended
General Guidelines
-create environment that allows free information exchange
-avoid technical jargon
-have the user duplicate the problem
-take notes

Problem Isolation
-divide an conquer
-change one component at a time

URL’s
www.scsifaq.org