Page 105 - DCAP303_MULTIMEDIA_SYSTEMS

Unit 6: Hardware

use a single wire that ends in a terminator with a ground. Ultra-2 SCSI sends the signal over two notes
wires with the data represented as the difference in voltage between the two wires. This allows
support for longer cables. A LVD reduces power requirements and manufacturing costs.
The latest SCSI standard is Ultra-3 (sometimes spelled “Ultra3”)which increases the maximum
burst rate from 80 Mbps to 160 Mbps by being able to operate at the full clock rate rather than
the half-clock rate of Ultra-2. The standard is also sometimes referred to as Ultra160/m. New
disk drives supporting Ultra160/m will offer much faster data transfer rates. Ultra160/m also
includes cyclical redundancy checking (CRC) for ensuring the integrity of transferred data and
domain validation for testing the SCSI network.

Currently existing SCSI standards are summarized in the Table 6.1.
table 6.1 The SCSI Standards

technology name Maximum Maximum Maximum number
Cable Length speed (Mbps) of Devices
(metres)
SCSI-1 6 5 8
SCSI-2 6 5–10 8 or 16
Fast SCSI-2 3 10–20 8
Wide SCSI-2 3 20 16
Fast Wide SCSI-2 3 20 16
Ultra SCSI-3, 8-bit 1.5 20 8
Ultra SCSI-3, 16-bit 1.5 40 16
Ultra-2 SCSI 12 40 8
Wide Ultra-2 SCSI 12 80 16
Ultra-3 (Ultra160/m) SCSI 12 160 16

6.2.3 enhanced integrated Drive electronics (eiDes)

Enhanced (sometimes “Expanded”) IDE is a standard electronic interface between your computer
and its mass storage drives. The EIDE’s enhancements to IDE make it possible to address a hard
disk larger than 528 Mbytes. The EIDE also provides faster access to the hard drive, support for
direct memory access (DMA), and support for additional drives, including CD-ROM and tape
devices through the AT Attachment Packet Interface.
When updating your computer with a larger hard drive (or other drives), an EIDE “controller”
can be added to your computer in one of its card slot.
To access larger than 528 M byte drives, EIDE (or the basic input/output system that comes
with it) uses a 28-bit Logical Block Address (LBA) to specify the actual cylinder, head, and sector
location of data on the disk. The 28 bits of the LBA provide enough information to specify unique
sectors for a device up to 8.4 GB in size.
The IDE interface cable has two plugs and can be attached to two devices. The first device acts as
the master, and the second device acts as a slave. This interface is busy if either device is processing
a request, so activity on one device blocks access to the other. It will generally be necessary when
adding a new disk to a system to set a switch or connector on the disk to indicate if it is to function
as master or slave.
When they designed the EIDE standard, they needed compatibility with all the existing IDE
devices. So they did not change the rules on the cable. The EIDE interface chip can support four
devices, but it has two interface cables each connecting two devices. The EIDE chip looks and acts
like two IDE chips. An old IDE disk can be connected to a new EIDE connector.

LoveLy professionaL University 99