Universal Serial Bus (USB)

The Universal Serial Bus (USB) is a relatively new technology that is designed to resolve all of the issues related to connecting peripheral devices to a workstation.

It eliminates the need to open computer case for installing cards needed for certain devices, and designed to meet Microsoft Plug and Play (PnP) specification.

USB also allows 127 devices to run at the same time on the bus using only one interrupt, it has dual-speed data transfer, 1.5Mbps and 12Mbps, and can provide limited power, (maximum 500mA of current) to devices attached on the bus.

SCSI Controllers

SCSI (Small Computer Systems Interface, pronounced "scuzzy") is a parallel interface standard used to connect devices to a PC. Although most manufacturers prefer to use the new usb interface for external peripherals, SCSI controllers and hard drives are still a very popular in servers that require high speed disk access and support for raid.

PC Case

PC case is a thin sheet metal enclosure that houses the motherboard, power supply and various drives (HDD, FDD, CD, DVD).

Cases are offered in two styles, desktop and tower. Today the tower type is predominant. It stands upright and is much taller than it is wide. It is usually placed on the floor next to, or under a desk. The desktop has a pizza box profile and usually sits on the desktop.

Tower cases are offered in two basic sizes, one that can fit ATX (12" wide) motherboards and one that can accommodate ATX mini (8.5" wide) motherboards. The number of drive bays offered also varies depending on manufacturer.

The motherboard and power supply mount to the floor at the rear of the case. The drives (hard, floppy and CD/DVD) mount in enclosures called drive bays at the front of the case.

Cases run from $20 to $70 depending on size (ATX or ATX mini), number of drive bays and the wattage of the power supply.

Power Supply

A power supply is installed in the back corner of the PC case, next to the motherboard.
It converts 120vac (standard house power) into DC voltages that are used by other components in the PC.

A 20 conductor cable carries +5vdc, -5vdc +12vdc, -12vdc and ground to the motherboard.

Another pair of cables, each with four conductors and two 4-pin connectors daisy-chained along it, carry +5vdc, +12vdc and ground to the drives (hard, floppy and CD/DVD).

Typical PC power supplies are rated at 200-250 watts and sell for about $50 - $75. Higher wattage supplies are available.

Digital Video Disk drive

DVD also known as the Digital Versatile Disk drive, installs in one of the external 5 1/4 inch drive bays in the PC. It is secured by machine screws. Some manufacturers offer special rail-like systems that mount on the DVD. These allow the drive to be removed from the PC without having to remove screws.

It is designed to optically access data stored on a DVD. A laser moves back and forth near the disk surface and accesses data at a very fast rate.

A 4-pin cable from the power supply plugs into the CDD and provides power to it.
Data between the DVD drive and the motherboard is carried on a 40-pin IDE (Integrated Drive Electronics) cable.

There are two types of DVD drives that typically go into PCs.

DVD-ROM (Read Only Memory) can read DVDs and CDs and costs about $75.

DVD-RAM (Random Access Memory) units can read and write DVDs. They can also read CDs and cost about $500.

A standard DVD stores up to 4.7 Gbytes on one side of the disk. Digitally formatted movies can be stored on a standard DVD in MPEG-2 format.

Audio

Speakers and headphones are the primary audio output devices for a PC.

Some monitors have speakers built into their sides. Other speakers are free standing.

Passive speakers plug into and are powered directly from the output signal provided by the 'speaker out' port on the sound card.

Active speakers amplify the sound signal from the sound card using battery or rectified AC house power.

Cables and Wires

• Although these are not the most sophisticated part of the system, they are just as important as any other component.


• All the components in a PC are connected together and to power with wires and cables.

• Ninety percent of all electronics problems (including PCs) are the result of poor connections.


• If you have a PC problem, it is always a good idea to first check that all the cables on your PC are plugged in and properly seated.