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A+ Core Technologies - Cram Session
PC
Ports
Parallel
ports:
 | 25
Pin female, "D" connector
|
| Sends
and receives 8 bits of data at a time
|
| Sends
data synchronously |
Serial
ports:
| 25
Pin male, "D" connector or 9 Pin
male, "D" connector
|
| Sends
and receives 1 bit of data at a time
|
| Sends
data asynchronously |
Keyboard:
| DIN-5
or PS2 |
Mouse:
| 9
Pin serial or PS2 |
Video:
| HDA=
15 pin female, 3 rows of pins. (Current VGA
and SVGA only) |
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Cables
and Connectors
-
Tape,
removable, hard, and optical drives along with
scanners can all use SCSI connections.
Up
to eight devices (including the controller) can be
chained off of a SCSI port. (SCSI id 0-7)
18
feet is the maximum length that a SCSI cable can
support.
Most
external SCSI devices have Centronics-50 or female
DB-25 connectors utilizing a male-to-male SCSI cable
(although there are newer 68 pin connectors and
other connectors as well).
Most
SCSI Host Adapters must be set to SCSI ID 7.
Null
modem cables or serial cables are used to transmit
data between 2 DTE devices..
Because
of interference, you have to reduce transfer rates
the longer a cable is.
50
feet is the maximum length that a serial cable
should be.
Phone
lines (few network) cables use RJ11 or RJ12
connectors. Connector resembles a small phone jack.
Twisted
pair cables use RJ45 connectors. Connector resembles
a fat phone jack.
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COM
Ports
-
COM1
and COM3 use IRQ4.
COM2
and COM4 use IRQ3.
The
majority of PC's have only 2 COM port connectors.
BIOS
-
BIOS
(Basic Input Output System) - Built-in software
that contains low level software for configuring
the system's capabilities with hardware.
System
Assembly Basics
-
Phillips
and Flat-Head screw drivers are the most common
tools needed for disassembly.
Paper
should be at hand for diagramming connections.
Egg
cartons are helpful in keeping screws organized.
Expansion
boards should be removed by gently rocking back and
forth at each end.
Red
and blue stripes on ribbon cables indicate pin 1.
Field
replaceable units (or FRU's) are any computer parts
that can be replaced without special equipment such
as soldering irons.
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System
Board Repair
-
Mother
boards, system boards, planar board, and main
logic boards are all interchangeable terms.
Older
XT planar boards used DIP settings for floppy
configuration.
Modern
AT system boards use SETUP in the BIOS.
SETUP
should always be ran after motherboard replacement
to reconfigure the system for customers.
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Busses
| ISA |
8-bit or 16-bit |
| EISA |
32-bit |
| PCMCIA |
16-bit |
| AGP |
32-bit |
| PCI |
64-bit (Most implementations
are 32-bit) |
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IRQ
(Interrupt Requests)
| IRQ 0 |
System Timer |
| IRQ 1 |
Keyboard |
| IRQ 2(9) |
Video Card or cascade to IRQ 9 |
| IRQ 3 |
Com2, Com4 |
| IRQ 4 |
Com1, Com3 |
| IRQ 5 |
Available (Normally LPT2 or sound card ) |
| IRQ 6 |
Floppy Disk Controller |
| IRQ 7 |
Parallel Port (LPT1) |
| IRQ 8 |
Real-time clock |
| IRQ 9 |
Redirected IRQ2 |
| IRQ 10 |
Available |
| IRQ 11 |
Available |
| IRQ 12 |
PS/2 Mouse |
| IRQ 13 |
Math Coprocessor |
| IRQ 14 |
Hard Disk Controller |
| IRQ 15 |
Available (often used for second Hard Disk
Controller) |
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I/O
Ports
| COM1 |
3F8H |
| COM2 |
2F8H |
| COM3 |
3E8H |
| COM4 |
2E8H |
| LPT1 |
378H |
| LPT2 |
278H |
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Processors
-
Floating-point
numeric operations are dealt with by the math
coprocessor.
The
80386SX uses the 80387SX as its fastest coprocessor,
and has a 32-bit word size and 16-bit data path.
The
80386DX uses the 80387DX as its fastest coprocessor,
and has a 32-bit word size and data path.
The
80486SX has a disabled coprocessor, and 32-bit word
size and data path.
A
486DX2's external clock speed is half of the
internal clock speed.
A
486DX4's external clock speed is 1/3 of the internal
clock speed.
Protected
mode is a processor feature that allows 2 or more
programs run without interfering with one-another.
Superscalar
- Two chips inside; one for parallel processing
and the other for fault tolerance.
Instructions
/ clock cycle - 4 instructions, 2 on each path.
MMX:
1)
57 instructions for manipulating video, audio
and graphic data
2) SIMD: Single Instruction Multiple Data
3) More build-in cache on chip
Dynamic
Execution (Pro):
1)
Multiple branch prediction Predicts when
instructions are to be processed
2) Dataflow analysis Analyzes instructions
3) Speculative execution
Pentium
II System Bus allows multiple simultaneous
transactions.
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Memory
ROM
(Read-Only Memory):
| ROM
is a form of non-volatile memory.
|
| Contains
both POST and SETUP. |
NVRAM
(Non-Volatile Memory):
| Can
maintain data without the use of power. |
CMOS:
| Contains
the computer setup data used by BIOS.
|
| Maintains
its data with the use of a battery for periods
when the machine is powered down. |
RAM
(Random Access Memory):
| RAM
is volatile memory and does not retain data
without power.
|
| RAM
contains any active application, including the
operating system. |
HMA
(or high memory area) is the first 64K of extended
memory.
Conventional
memory is the first 640K of memory.
Upper
memory is the memory between 640K and 1024K. Used to
load DOS drivers to allow applications more
conventional memory.
Extended
memory is the memory above 1024K.
Expanded
memory is addressed in pages of 16K.
The
suspend mode of portables often causes problems with
the expanded memory manager.
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Drives
-
When
transferring data, copying data from one drive to
another is the best method of data protection.
A
cluster is a group of sectors.
Sectors
are aligned in tracks.
The
seek time is the time that is takes the head to
reach the needed track.
The
latency period is the time that it takes the sector
to move under the head.
The
overall time it takes a hard drive to find data is
the access time.
The
data transfer rate is how fast the hard drive sends
data to the PC.
The
BIOS in older systems may not support large hard
drives, and must be upgraded before installation.
With these BIOSes, you can upgrade (flash or
replace) the ROM Bios chip, replace the motherboard,
buy an EIDE controller card, or use DDO (disk drive
overlay) software to support larger hard drives. The
BIOS limit for older controllers was 504 megabytes
(sometimes listed as 528 MB because 504 megabytes is
528,482,304 bytes).
The
physical or low level format is rarely needed.
To
prepare a hard disk for use, setup a partition on
the disk, format the partition, then load the OS.
FDISK
and PART (found on older versions of DOS) are the
programs used for setting up partitions.
Always
back up hard drives before formatting.
FORMAT.COM
- Program used for DOS formatting.
FORMAT
/Q performs a quick format.
FORMAT /S switch tells FORMAT to copy system boot
files to the disk.
Physical
drives are actual separate drives while logical
drives concern partitions on the physical drives.
To
write protect a 3.5 floppy, uncover the hole in the
upper-right hand corner of the diskette.
To
write protect a 5.25 floppy, cover the notch on the
side of the diskette.
Computers
detect HDD (high-density) 3.5 floppies by the hole
in the upper left corner.
FDD
controllers use DMA channel 2 in most cases.
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HDI
= Head to Disk Interference
|
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Controllers
-
Controllers
match speeds between sending and receiving
devices, convert data between formats, and isolate
the software from the hardware.
A
DTE device in general, is a device such as a
computer or printer.
A
DCE device is a device such as a modem.
A
terminal sends the Ready To Send signal when it
transmits to a DCE device such as a modem.
A
modem must have the Carrier Present signal before it
is able to receive.
RS232
is the standard for serial connections.
DMAs
(Direct Memory Access) work with the CPU, letting
devices put data into memory rather than the CPU,
therefore helping to speed transfer rates.
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Monitors
-
The
picture element (PIXEL) is the smallest point that
can be controlled on a monitor display screen.
The
refresh rate is the number times display is
redrawn every second.
| CGA |
640 x 200 |
| EGA |
640 x 350 |
| VGA |
640 x 480 |
| SVGA |
1024 x 768 |
Networking
-
Coaxial,
twisted pair, and fiber optic cables are all used
in networking.
A
token ring network passes packets of data called
tokens to each station in a network.
LAN
- Local Area Network
|
WAN
= Wide Area Network
|
|
MAN
= Metropolitan Area Network
|
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Fiber-Optic
- Cables designed for high transfer rates over
large distances; carry light pulse signals
through glass core at speeds of between
100Mbps - 1Gbps.
Ethernet
can use coaxial and twisted pair wiring, and can
support speeds of 10mbps - 100mpbs. |
|
10Base5
- 10 Mbps transfer rate with thick coaxial
cable.
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10Base2
- 10 Mbps transfer rate with thin coaxial
cable.
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10BaseT
- 10 Mbps transfer rate, baseband
transmission, with twisted pair wire.
|
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100BaseT
- 100 Mbps transfer rate, baseband
transmission, with twisted pair wire.
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Troubleshooting
-
When
replacing a power supply pay special attention to
the physical characteristics, the voltage and
connectors are standardized.
Rom
addresses, I/O addresses, IRQs, and DMA channels can
all cause conflicts.
IRQ
conflicts are the most common conflict, because
there are so few IRQs compared to the many
peripherals that can be installed into a system.
If
a battery test fine after a boot configuration
error, the most likely cause is the system board.
Always
carefully examine any shipped in merchandise before
installation and powering the system on.
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Preventative
Maintenance and Safety
-
Almost
all computer equipment should be cleaned with only
a soft, damp cloth with a mild detergent.
ESD
(Electro-Static Discharge) - Prevention of having
electric currents damage system components.
Compressed
air it most effective for removing dust because of
the pressure, directability, and less chance of ESD
damage.
Line
analyzers are used for detecting line surges, sags,
and spikes.
Hard
drives should be defragmented and backed up often.
Hard
drives should be protected from both magnetic fields
and temperature extremes.
Never
lubricate the printhead pins of a dot matrix printer
during preventative maintenance.
Never
wear a wrist strap while working on a monitor CRT
because the stored voltage is capable of killing a
person.
ESD
will degrade a components integrity. Although not
immediately seen, the effects could show up months
later.
Any
amount of friction is enough to cause enough static
to cause ESD.
To
avoid ESD use a wrist strap, and always ship items
in ESD safe bags.
Nylon,
plastic, wood, and vinyl are not ESD safe materials.
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Printers
Laser
Printers:
The
ozone filter needs to be replaced on laser
printers when performing preventative maintenance.
For
dark spots on a page with a laser printer, it
indicates loose toner particles. Running extra
paper through will usually resolve it.
The
order of processes in a laser printer is:
1)
Cleaning
2) Conditioning
3) Writing
4) Developing
5) Transferring
6) Fusing
The
primary corona has the highest negative charge in
a printer.
Always
check where the leading edge of paper is when
troubleshooting paper jams, because it can
indicate which printer part is causing the jam.
The
photoconductive drum in a laser printer is charged
negatively, and loses its charge when light hits
it.
The
transfer corona can cause the print to be too
light.
Dot
Matrix:
A
tight ribbon can cause flecks and smudges on the
paper.
Missing
or broken printhead pins causes incomplete
characters.
Never
lubricate the printhead on a printer.
If
the print density is erratic, then there may be an error with the ribbon advance.
Modem
Commands
| Command |
Function |
| ATA |
Answer |
| ATD |
Dial |
| ATZ |
Reset |
| ATF1 |
Half-Duplex Off (echo copy of receiving
information) |
| ATHN |
Hang up |
| ATMN |
Speaker On/Off |
| ATSR |
Display register |
| ATH |
Hangs up modem |
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PCMCIA
| Type 1 |
3.3mm |
Memory |
| Type 2 |
5 mm |
Modems, Network cards |
| Type 3 |
10.5 mm |
Hard Disks |
Socket
Services - BIOS level software interface for
hardware information.
|
Card
Services - I/O, IRQ hardware interface with
computers.
|
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CIS
(Card ID Structure) - Cards describe
themselves to other devices.
PCMCIA
cards use very little power and can be
hot-swapped.
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Power
Supplies
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Yellow:
+12
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Blue:
-12
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Red:
+5
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White:
-5
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Voltage
for motor: +/- 12 volts
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Voltage
for circuitry: +/- 5 volts
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