Page 104 - DCAP303_MULTIMEDIA_SYSTEMS

Multimedia Systems

notes The IDE devices use a ribbon cable to connect to each other. Ribbon cables have all of the wires
laid flat next to each other instead of bunched or wrapped together in a bundle. The IDE ribbon
cables have either 40 or 80 wires. There is a connector at each end of the cable and another one
about two-thirds of the distance from the motherboard connector. This cable cannot exceed 18
inches (46 cm) in total length (12 inches from first to second connector, and 6 inches from second
to third) to maintain signal integrity. The three connectors are typically different colours and
attach to specific items:
• The blue connector attaches to the motherboard.
• The black connector attaches to the primary (master) drive.

• The grey connector attaches to the secondary (slave) drive.
enhanced iDe (eiDe)—an extension to the original ATA standard again developed by Western
Digital—allowed the support of drives having a storage capacity larger than 504 MiBs (528 MB), up
to 7.8 GiBs (8.4 GB). Although these new names originated in branding convention and not as an
official standard, the terms IDE and EIDE often appear as if interchangeable with ATA. This may
be attributed to the two technologies being introduced with the same consumable devices—these
“new” ATA hard drives. With the introduction of Serial ATA around 2003, conventional ATA
was retroactively renamed to Parallel ATA (P-ATA), referring to the method in which data travels
over wires in this interface.

6.2.2 small Computer system interface (sCsi)
The Small Computer System Interface (SCSI) is a set of ANSI standard electronic interfaces that
allow personal computers to communicate with peripheral hardware such as disk drives, tape
drives, CD-ROM drives, printers, and scanners faster and more flexibly than previous interfaces.
Developed at Apple Computer and still used in the Macintosh, the present set of SCSIs are
parallel interfaces. The SCSI ports continue to be built into many personal computers today and
are supported by all major operating systems.
In addition to faster data rates, SCSI is more flexible than earlier parallel data transfer interfaces.
The latest SCSI standard, Ultra-2 SCSI for a 16-bit bus can transfer data at up to 80 megabytes per
second (mbps). The SCSI allows up to 7 or 15 devices (depending on the bus width) to be connected
to a single SCSI port in daisy-chain fashion. This allows one circuit board or card to accommodate
all the peripherals, rather than having a separate card for each device, making it an ideal interface
for use with portable and notebook computers. A single host adapter, in the form of a PC Card,
can serve as a SCSI interface for a laptop, freeing up the parallel and serial ports for use with an
external modem and printer while allowing other devices to be used in addition.

Although not all devices support all levels of SCSI, the evolving SCSI standards are generally
backwards-compatible. That is, if you attach an older device to a newer computer with support
for a later standard, the older device will work at the older and slower data rate.
The original SCSI, now known as SCSI-1, evolved into SCSI-2, known as “plain SCSI” as it became
widely supported. The SCSI-3 consists of a set of primary commands and additional specialized
command sets to meet the needs of specific device types. The collection of SCSI-3 command sets
is used not only for the SCSI-3 parallel interface but for additional parallel and serial protocols,
including Fibre Channel, Serial Bus Protocol (used with the IEEE 1394 Firewire physical protocol),
and the Serial Storage Protocol (SSP).

A widely implemented SCSI standard is Ultra-2 (sometimes spelled “Ultra2”) which uses a 40 MHz
clock rate to get maximum data transfer rates up to 80 Mbps. It provides a longer possible cabling
distance (up to 12 metres) by using low voltage differential (LVD) signalling. Earlier forms of SCSIs

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