ON THIS PAGE ,YOU WILL FIND,SCSI DEFINED,
ALONG WITH CABLES OF,INCLUDING ALT 1 AND 2,
A AND B,L,P,AND Q.ALSO ARE ALL
OF THE CABLE
LENGHTS,CONNECTORS AND TRANSFER RATES.AS WELL
AS RAID,INCLUDING RAID O,1,3,AND 5.
SMALL COMPUTER SYSTEM INTERFACE
IS A COLLECTION OF INTERFACE STANDARDS THAT COVERS
A WIDE RANGE OF
PERIPHERAL DEVICES,INCLUDING HARD
DRIVES,TAPE DRIVES,CD-ROM'S,AND RAID.
( REDUNDANT ARRAY OF INDEPENDENT DISKS )
The single most critical item in the installation of a successful,high-reliability,maximum throughput SCSI system.
The longer the cables and the faster the data
throughput,the more critical cables become.
cables are usually non-shielded
ribbon cables and external cables are usually
round,shielded cables with shielded
Cable impedance must be matched to the
requirements of SCSI devices and cable pairs
must be carefully
selected for the correct SCSI
Alt 1 Cable -
An A-cable having 50-pin male high-density
micro-D connectors with spring-latch fasteners.
May be nonshielded or shielded.
Alt 2 Cable -
having 50-pin male Centronics-type connectors
for round,shielded cabling or two rows of 25 pins on
0.1 inch centers
for internal nonshielded ribbon cabling.
A 50 pin narrow SCSI cable.See Alt 1 and Alt 2
for the 4 types of A-Cable.
Identical in construction to the A-cable introduced
in SCSI-2 for
use with WIDE SCSI.Never popular because
of requirement for two cables.The B-cable was rendered
obsolete by the introduction
of the P-cable in SCSI-3.
Use of WIDE SCSI immediately began to increase.
L-Cable - A 110-pin high-density
connector considered for use in 32-bit WIDE SCSI
systems.No longer viable as 32-bit SCSI was
in the SPI-3 document of SCSI-3.
In SCSI-3,the P-cable is defined for 16-bit
systems to eliminate the necessity
to use two cables an A-cable and a B-cable)
for 16-bit WIDE SCSI.Uses 34 twisted
(68 wires)and 68-pin high-density male micro-D
connectors with 2-56 thumbscrew fasteners.
Physically and electrically identical to the P-cable.
Both a P-cable and a Q-cable were specified for 32-bit
SCSI buses.This cable is no long viable as 32-bit
wide SCSI was rendered obsolete in the SPI-3 document
CABLE LENGHTS :
The SCSI specifications provide maximum recommended
cable lengths for various implementations
It is further Recognized that in "engineered"
installations these cable lengths may be exceeded.
Maximum recommended SCSI cable lengths:
-SCSI TYPE - SPEED---MAX CABLE LENGTH
SINGLE ENDED - SLOW
(FAST-5) 6 Meters / 19.7 Feet
SINGLE ENDED - FAST (FAST-10) 3 Meters / 9.8 Feet
SINGLE ENDED -
ULTRA (FAST-20) 1.5 Meters* / 4.9 Feet
Maximum cable length with eight addresses.
May be up to 3 meters With four
DIFFERENTIAL (HVD) -(ANY SPEED) 25 Meters / 82 Feet
LVD -ULTRA2,ULTRA3 or ULTRA4 12 Meters
/ 39.4 Feet
This may be increased to 25 meters
(82 Feet in point to point applications.
IDC HEADER :
50 pin insulation displacement connector(IDC)
used with ribbon
cables for nonshielded,
internal SCSI cabling.Female type used on cables.
CENTRONICS TYPE :
This connector is a 50-pin version of the connector
used for parallel printer
ports for years.Specified
in SCSI-1 and still an acceptable connector for narrow
SCSI.Male connector used for cables,female
Uses bail fasteners on the device-mounted female
connector to secure the male connector.Often referred
to as the "SCSI-1" connector.
Shielded Alternative 1, A-cable.
HIGH-DENSITY MICRO-D CONNECTOR -
PIN AND SOCKET CONNECTOR :
Smaller than the centronics-type.Specified to
spring-latch fasteners.Male connector used
on cables;female on devices.
68-pin Micro-D high-density-
Originally specified in SCSI-3 to allow the use
of one cable for
This cable is called a P-cable.68-pin version
of the 50-pin micro-D high-density connector.
Although the 2-56 thumbscrew fastener is specified
in SCSI-3,some manufacturers have used the spring-latch
connector used on cables;female on devices.
Frequently referred to as the "SCSI-3" connector.
Shielded (or non-shielded)Alternate 3,P-cable.
68-pin VHDCI (Very High Density Cable Interconnect)
specified in SCSI-3.Ribbon contact
construction similar to centronics type connector,
but on smaller 0.8 mm(0.0315")pitch.Much
footprint allows up to four connectors to be mounted
on a PC backplate.Called the VHDCI connector.
Shielded Alternate 4 - P cable.
80-pin SCA (Single Connector Adapter) -
in the SCSI-3 specifications
for device connection on hot-swap backplanes.Device
ID is assigned by the backplane and
are included on the connector,so using peripherals with
an SCA connector in a cabled system requires
of an SCA to 68 pin (or 50 pin)adapter with provisions
for peripheral power and assignment of ID.
Non-shielded Alternate 4 - P cable.
DB-25 - Not specified
in the SCSI specifications,
this 25-pin connector can support SLOW 8-bit(narrow)
SCSI only and then only with very
Apple Macintosh version became a de facto standard
totally incompatible with the pinout of the old -
Future Domain 25-pin SCSI connector).Male connector
on cable;female on devices.
30-pin HDI -
connector created by Apple for
reduced mounting space on their PowerBook notebooks.
Not suitable for multiple SCSI
devices or long cables
because there are only 30 pins.
DB-50, D-sub connector was used on some older
and DG computers for Narrow SCSI applications.
50 pins arranged in three rows.
60-pin high-density -A non-standard
by IBM.Early in the process of writing the
SCSI-2 specification,the ANSI X3T9.Two committee
a 60-pin connector for 8-bit SCSI that
was later abandoned,IBM,however,retained this connector
for their PS/2 systems.It
is a 60-pin high-density
micro-D male connector with spring-latch fasteners.
The first 50-pin assignments are identical
SCSI-2 high-density pinout and pins 51 to 60
are designated as "reserved".
MORE SCSI CONNECTOR
END P = MALE
S = FEMALE
RC - 50 P/S -------FULL-PITCH
DB - 25 P/S--------FULL-PITCH D-SUB 25-PIN
DB - 50 P/S -------FULL-PITCH D-SUB 50-PIN
RCII -50 P/S------CENTRONIC HALF-PITCH
---------------------- MICRO CONNECTOR 50 PIN
DBII - 50 P/S----D-SUB
-------------------------- CONNECTOR 50 - PIN
RC3 -68 P/S-------CENTRONIC HALF-PITCH
MICRO CONNECTOR 68 -PIN
DB3 - 68 P/S ------D - SUB HALF-PITCH MICRO
------------------------CONNECTOR 68 - PIN
SCSI - 1 ( ASYNCHRONOUS )--2 Mbps
SCSI - 1 ( SYNCHRONOUS )---- 5 Mbps
SCSI - 2 FAST-----------------------10 Mbps
SCSI - 2 16 - BIT- WIDE----------10 Mbps
SCSI-2 FAST AND
SCSI -2- 32 BIT-WIDE--------------- 20 Mbps
SCSI -2-FAST AND 32-BIT-WIDE--40 Mbps
WHEN SCSI-2 AND SCSI-3 DEVICES FIRST CONNECT ASYNCHRONOUSLY,THEY HANDSHAKE IN 8-BIT NARROW MODE TO ENSURE THAT THE
DATA WILL TRANSFER PROPERLY.THE INITIATOR AND TARGET THEN NEGOTIATE THE MAXIMUM MUTAL CAPABILITIES.
SPEED-----FREQUENCY-----NARROW SPEED----WIDE SPEED
SCSI---------5MHz-----1,5 to 5 MB/s---/[no wide device]
SCSI----10MHz--------10 MB/s---------------20 MB/s
Ultra SCSI---20MHz--------20 MB/s---------------40 MB/s
Ultra2 SCSI---40MHz-------40 MB/s----------------80 MB/s
Ultra 160/m--80MHz--/ [no narrow device]---- 160 MB/s
REDUNDANT ARRAY OF INDEPENDENT DISK
IS A STORAGE TECHNOLOGY THAT USES TWO OR MORE HARD
DRIVES IN COMBINATION
FOR HIGH AVAILABILITY,
FAULT TOLERANCE,AND PERFORMANCE.
RAID 0 - DATA STRIPING :
INTERLEAVES DATA ACROSS MULTIPLE DRIVES.
DOESN'T INCLUDE MIRRORING,REDUNDANCY,
OTHER PROTECTION AGAINST DEVICE
FAILURE.IT IS NOT FAULT TOLERANT
RAID 1 - DATA MIRRORING :
TOLERANCE BY COMPLETELY DUPLICATING
DATA ON TWO INDEPENDENT DRIVES.IN CASE ONE OF THE
MIRRORED DRIVES FAIL.
3 - PARALLEL TRANSFER WITH PARITY :
PROVIDES FAULT TOLERANCE BY TRANSFERING DATA TO AND
FROM THREE OR MORE HARD DRIVES
WITH DATA STRIPED ACROSS
THE DRIVES AND THE PARITY BITS,WHICH ARE USED TO RECON-
STRUCT THE DATA IN THE EVENT OF A
DRIVE FAILURE AND STORED ON A SEPERATE AND DEDICATED DRIVE.
RAID 5 - DATA STRIPING WITH PARITY :
TOLERANCE BY EMPLOYING ESSENTIALLY THE
SAME APPLICATION AS RAID 3.HOWEVER,RAID 5 STORES THE
PARITY BIT FROM TWO DRIVES
ON A THIRD DRIVE TO PROVIDE
FOR DATA STRIP ERROR CORRECTION.THIS IS THE MOST POPULAR RAID TECHNOLOGY USED TODAY.