[ale] What is ultra-scsi vis-a-vis say,.... scsi2 ?

Sun Apr 14 00:35:34 EDT 2002

Courtney Thomas wrote:
> Greetings !
> 
> Please distinguish between the scsi varieties or please point me
> to a URL that will.
> 
> Thank you,
> Courtney
> 

from http://www.paralan.com/glos.html

SCSI - Small Computer Systems Interface:
     An intelligent peripheral I/O interface with a standard, device independent protocol that allows many different peripheral devices to be attached to the host's SCSI port. Allows up to 8, 16 or 32 addresses on the bus depending on the width of the bus. Devices can include multiple hosts (initiators) and peripheral devices (targets) but must include a minimum of one of each. 32 bit SCSI was rendered obsolete in the SPI-3 document of SCSI-3. See SCSI-1 X3.131-1986.

SCSI-1:
     A derivative of SASI. Specification first released by ANSI in 1986 as X3.131-1986. Originally included synchronous and asynchronous data transfers at speeds up to 5 Megatransfers per second (5 MBytes/sec for 8 bit). Defined the single-ended narrow interface with the "idc" internal connector and the centronics type external connector. Did not include definitions of a device independent interface.

SCSI-2:
     The next generation of SCSI by ANSI Committee X3T9.3 and released as specification X3.131-1994 in January of 1994. Arguably the most significant addition of SCSI-2 is the expanded definition of the common command set (CCS). Defines 16-bit and 32-bit WIDE data bus. Increases the maximum data throughput to 10 Megatransfers /second (10 MBytes/ second for 8-bit; 20 Megabytes/second for 16-bit; and 40 Megabytes/second for 32-bit). Added the smaller 50-pin high-density micro-D connector. Strongly recommends active terminators for single-ended bus. Backward compatible with SCSI-1.

SCSI-3:
     An ANSI Committee X3T10 work in progress. With the new SCSI Architecture Model, a "SCSI-3" specification will not be published. Instead, a collection of stand-alone documents, each with its own rev number will be introduced. These documents include enhancements for parallel SCSI as well as definitions for serial SCSI to allow interface to serial buses such as Fibre Channel, SSA and FireWire. Parallel SCSI enhancements include Ultra SCSI (also called Fast-20) which doubles SCSI-2 speeds to a maximum data throughput of 20 Megatransfers/second (20 MBytes/sec for 8-bit SCSI; 40 MBytes/sec for 16-bit SCSI). The SPI-2 document of SCSI-3 includes Ultra2 SCSI 
(also called Fast-40) which doubles these data throughputs again and requires low voltage differential (LVD) signalling for 80 Mbyte/sec transfers.
The Ultra 160 (also called Fast 80) interface will be found in SPI-3 for 160 Mbyte/sec data transfers. SPI-3 obsoletes the 32-bit wide interface, the high voltage differential (HVD) interface and SCAM. Future enhancements will include 320 MBytes/second transfers. SCSI-3 defined a single cable (the P-cable) to eliminate the necessity to use two cables (the A-cable and B-cable) for 16-bit SCSI. The EPI document of SCSI-3 includes definitions for expanders including SCSI enhancement devices such as converters. The new interfaces are backward compatible with SCSI-2 as well as SCSI-1 via the single-ended interface.

Ultra 320:
     Refer to Ultra4.

Ultra SCSI:
     Also called "Fast-20". An enhancement of SCSI that results in doubling the FAST SCSI data throughput speeds to 20 MBytes/sec for 8-bit and 40 MBytes/sec for 16-bit. Reduces maximum allowable single-ended SCSI cable length to 1.5 meters (4.9 feet) for five to eight addresses and 3 meters (9.8 feet) for four or fewer addresses. Maximum allowable differential (HVD) SCSI cable length is 25 meters (82 feet). Defined in the SPI document of the SCSI-3 specification.

Ultra2 SCSI:
     Also called "Fast-40". An enhancement of SCSI that results in doubling the Ultra SCSI data throughput speeds to 40 Megatransfers/sec (40 MBytes/sec for 8-bit and 80 MBytes/sec for 16-bit). The SCSI specification recognizes only LVD Ultra2 SCSI and single-ended is not defined at this speed. Maximum allowable Ultra2 cable length is 12 meters (39.4 feet) with more than two active SCSI IDs or 25 meters point to point. Backward compatible through the single-ended interface using Ultra or slower speeds and cable lengths.

Ultra3 SCSI:
     Also called "Fast-80" or "Ultra160". Described in SPI-3, Ultra160 again doubles the data throughput speeds to 80 Megatransfers/sec (160 MBytes/sec for 16-bit). Single-ended not defined at this speed. Requires LVD signalling. SPI-3 also obsoletes HVD, SCAM and the 8-bit and 32-bit wide bus. U160/m is a sub-set of Ultra160 SCSI that includes double transition clocking, CRC and domain validation. Maximum allowable Ultra3 cable length is 25 meters (82 feet) point to point or 12 meters (40 feet) with more than two active SCSI IDs. Backwards compatible through the single-ended interface using Ultra or slower speeds and cable lengths.

Ultra4 SCSI:
Also called "Ultra 320" or "Fast-160". Again doubles the data throughput to 320 MBytes/sec. Defined in the SPI-4 document of the SCSI-3 specifications, Ultra 320 requires LVD signaling. To reduce overhead and increase data throughput Ultra 320 will include QAS and Information Units (packetizing). Maximum allowable Ultra4 cable length is 12 meters (39.4 feet) with more than two active SCSI IDs and up to 25 meters (82 feet) point to point. Ultra320 is backward compatible through the single-ended interface using Ultra or slower speeds and cable lengths. As with Ultra3 SCSI, single-ended is not defined at Ultra4 throughputs and HVD is obsolete.

Fast SCSI:
     Defined in the SCSI-2 specifications. Increased the maximum SCSI data throughput from 5 MBytes/second for 8-bit (NARROW) synchronous SCSI-1 to 10 Mbytes/sec. WIDE (16-bit) SCSI synchronous speed increased from 10 Mbytes/second to 20 Mbytes/ second. No effect on asynchronous SCSI speed.

Fast-20:
     Refer to Ultra SCSI

Fast-40:
     Refer to Ultra2 SCSI

Fast-80:
     Refer to Ultra3 SCSI Also known as Ultra160 or Ultra 160/m.

Fast-160:
     Refer to Ultra4 SCSI Also known as Ultra320.

Fast-Wide SCSI:
Usually refers to 16-bit (WIDE) SCSI with FAST data transfers of up to 20 MBytes/second. May also refer to 32-bit SCSI FAST data transfers (up to 40 MBytes/ second). Note that 32-bit wide SCSI was obsoleted in the SPI-3 document of SCSI 3.

also:

http://directory.google.com/Top/Computers/Hardware/Buses/SCSI/Standards/
http://www.adaptec.com/worldwide/support/supporteditorial.html?prodkey=SCSI_glossary

-- 
Lost in Tokyo,
   Keith

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