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SCSI
SCSI stands for small computer system interface. Pronounced "scuzzy,"
SCSI is a parallel interface standard used by Apple Macintosh computers,
PCs, and many UNIX systems for attaching peripheral devices to computers.
SCSI interfaces provide for faster data transmission rates (up to
320 megabytes per second) than standard serial and parallel ports.
In addition, you can attach many devices to a single SCSI port, so
that SCSI is really an I/O bus rather than simply an interface.
Typical SCSI Devices
Hard
Drives
CD/DVD ROM
Scanners
Tape Drives
Zip Drives
Removable Drives
Printers
SCSI chain – a series of SCSI devices working together through a host adapter
SCSI card or SCSI Host Adapter – comes as a PCI or ISA and has an internal and external connector that would connect to a device
scsi
host adapter
Whatever
devices are at the both ends of the SCSI chain must be terminated
Ways to terminate – PnP, software, jumper settings,
switch and using a terminator
Below
are examples of internal SCSI interfaces:
Below are examples of external SCSI interfaces:
DB25 (found on SCSI 1 and common in Macintosh computers)
SCSI 50
SCSI
68
SCSI ID – Each device on the SCSI chain must have a unique ID with 0 being the highest priority and 15 being the lowest priority and the SCSI card is usually ID 7
LUN – logical unit numbers allows a device to share an ID up to seven sub units per ID
SCSI Cables
SE - Single Ended system allows eight wires on the data cable
to carry data
HVD - High Voltage Differential employs two wires
per bit of data
LVD - Low Voltage Differential employs requires less
power than HVD
SCSI Flavor CHART
| SCSI Types | Bus
Speed (MB/s) |
Bus
Width (bits) |
SE (m) |
LVD (m) |
HVD (m) |
Maximum Device Supported | ID |
| SCSI-1 | 5 | 8 | 6 | 25 | 8 | 0-7 | |
| Fast SCSI 2 | 10 | 8 | 3 | 25 | 8 | 0-7 | |
| Fast Wide SCSI 2 | 20 | 16 | 3 | 25 | 16 | 0-15 | |
| Ultra SCSI 3 | 20 | 8 | 3 | 25 | 8 | 0-7 | |
| Ultra 2 SCSI 3 | 80 | 16 | 12 | 25 | 16 | 0-15 | |
| Ultra SCSI 160 (SCSI 3) | 160 | 16 | 12 | 5 | 16 | 0-15 | |
| Ultra 4 SCSI 320 (SCSI 4) | 320 | 16 | 12 | 5 | 16 | 0-15 | |
| Ultra 4 SCSI 640 (SCSI 5) | 640 | 16 | 12 | 16 | 0-15 |
Other
Types of SCSI
iSCSI use mostly for high end networking
SAS(Serial Attach SCSI) use for storage 300 use SFF 8482, 8484, 8470 connector and is use for high end Serial Transmission
(Narrow SCSI 8bit and Wide SCSI 16bit)
Ultra SCSI 3, 320 and 640 use 68 and 80 pins and uses Parallel Transmission
SCSI
– is used primarily in RAID drives and if the client wants the
ability to daisy chain and have fast devices.