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.
COM2 and COM4 use IRQ3.
The majority of PC's have only 2 COM port connectors.
Paper should be at hand for diagraming 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.
Older XT planar boards used DIP settings for floppy configuration.
Modern AT system boards use SETUP in the BIOS.
SETUP should always be run after motherboard replacement to reconfigure the system for customers.
|ISA||8-bit or 16-bit|
|PCI||64-bit (Most implementations are 32-bit)|
|IRQ 0||System Timer|
|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 12||PS/2 Mouse|
|IRQ 13||Math Coprocessor|
|IRQ 14||Hard Disk Controller|
|IRQ 15||Available (often used for second Hard Disk Controller)|
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.
Instructions / clock cycle - 4 instructions, 2 on each path.
Dynamic Execution (Pro):
Pentium II System Bus allows multiple simultaneous transactions.
NVRAM (Non-Volatile Memory):
RAM (Random Acces Memory):
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.
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 /Q performs a
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.
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.
|CGA||640 x 200|
|EGA||640 x 350|
|VGA||640 x 480|
|SVGA||1024 x 768|
A token ring network passes packets of data called tokens to each station in a network.
Ethernet can use coaxial and twisted pair wiring, and can support speeds of 10mbps - 100mpbs.
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 tests fine after a boot configuration error, the most likely cause is the system board.
Always carefully examine any new components before installing them and powering the system on.
Compressed air is most effective for removing dust because of the pressure, directability, and small 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 maintenence.
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 component's 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.
Dark spots on a page from a laser printer indicates loose toner particles. Running extra paper through the printer will usually resolve it.
The order of processes
in a laser printer is:
A mnemonic device for remembering this 6-step process is, "Canadians & Canucks Will Defeat The Flames"
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 has a negative charge, and loses its charge when light hits it.
The transfer corona can cause the print to be too light.
Missing or broken printhead pins cause incomplete characters.
Never lubricate the printhead on a printer.
If the print density is erratic, then there is probably an error with the ribbon advance.
|ATF1||Half-Duplex Off (echo copy of receiving information)|
|ATH||Hangs up modem|
|Type 2||5 mm||Modems, Network cards|
|Type 3||10.5 mm||Hard Disks|
PCMCIA cards use very little power and can be hot-swapped.