Small Computer System Interface

The Small Computer System Interface (SCSI) is a set of standards that dictate the physical connection between a computer and peripheral devices and the hardware and software implementation needed to make all that work together.

Even though nowhere as popular as it once was it is still pretty much a requirement for anyone doing low level programming to have at the least a basic understanding of the SCSI subsystem and the standard commands etc. Most if not all alternative data transport systems for peripheral devices copy the SCSI command structure to some degree and storage centred standards like SATA copy the command structure down to a tee, even though they are electrically very different systems. You are therefore going to find SCSI in the oddest of places when you are doing any programming that involves interfacing with storage systems of some sort.

In hardware terms SCSI still has a number of advantages over alternatives such as SATA, although its main advantage is of processing independence from the host was partially lost in the mid-90s on PC systems (PC architecture issue rather than an OS or driver issue).

Advanced SCSI Programming Interface

Better known as just ASPI, it is a programming interface introduced by Adaptec in the 1990s that simplifies the programming for end user applications that need to access a SCSI device or devices with compatible command interface such as ATAPI, most but not all SCSI drivers provide an ASPI interface. Most operating systems provide an ASPI interface for their ATAPI (IDE/SATA) implementation or have them as optional installs although with the decline in use of CD-ROM technology the use of ASPI has gone down as well.

SCSI over Ethernet

A networking protocol that allows computers to access storage devices and other peripherals to be accessed over Ethernet as if they where local SCSI devices, via encapsulation.

Fibre channel

High speed networking standard that is in practice mostly used to connect high speed storage devices to computer servers using a SCSI based protocol very similar to SCSI over Ethernet.

InfiniBand

A very high speed interconnect standard primarily used in high speed networking hardware, it allows for a form of iSCSI for peripheral or storage devices best described as "SCSI over InfiniBand".

USB Attached SCSI

Introduced with the USB version 3 specification but has also been made to work with USB 2. Basically replaces the USB Mass Storage Bulk-Only Transport (BOT) with the SCSI protocol. In general UAS is faster than the old BOT especially when dealing with SSD or other fast flash memory technology. At this point in time there are no OS/2 drivers for UAS.

Universal Flash Storage

Or UFS is a new(ish) standard for flash storage on consumer devices, the hardware interface part is either M-PHY or UniPro but the software interface copies SCSI.

Publications

Introductory material

• Friedhelm Schmidt: SCSI-Bus und IDE-Schnittstelle (4. Auflage) - Addison-Wesley 2001, ISBN 3827318289

A much improved fourth edition of this book, IDE in particular improved and all in all one of the better introductory texts but only available in German.

• Friedhelm Schmidt: The SCSI bus and IDE interface (2nd edition) - Addison-Wesley 1998, ISBN 0-201-17514-2

English translation of an older version

• Gary Field; Peter Ridge: Book of SCSI: I/O for the New Millennium (2nd edition) - No Starch Press 2000, ISBN 1886411107

This is targeted towards the beginner but as such is a rather good introduction.

• Brian Sawert: The Programmer's Guide to SCSI - Addison-Wesley 1998, ISBN 0-201-18538-5
• Louis Columbus: Exploring the World of SCSI - Prompt 2000, ISBN 0790612100

Targeted towards the end user rather than the programmer.

• Marc D. Brooks; Duane J. Stein; Barry B. Shiloff: Making SCSI Work Paralan Corporation 1999, ISBN 096574650X
• NCR Corp: SCSI: Understanding the Small Computer System Interface - Prentice Hall 1990, ISBN 0-13-796855-8

Well written and clear introduction, but outdated. Short, almost a booklet rather than a book.

• David Deming: The SCSI Tutor - ENDL 1995, ISBN 1879936089
• John Lohmeyer: SCSI Standards Architecture

A short article that explains what SCSI standards are out there, what they define and how they came to be.

• Nabeel ur Rehman, Asad Asif and Junaid Iqbal - SCSI Interface

Quite good introduction to SCSI and more modern than most of the above.

Reference works

• Seagate Corp. SCSI Commands Reference Manual - Includes Fibre Channel and SAS
• Jeffrey D. Stai:
  • The SCSI Bench Reference (3rd edition) - ENDL Publications 1997, ISBN 1879936305 - Aimed squarely at the technician rather than the software engineer, but as such very good although outdated.
  • SCSI Encyclopedia Phases & Protocols A-M - ENDL Publications 1991, ISBN 1879936119
  • SCSI Encyclopedia Phases & Protocols N-Z - ENDL Publications 1991, ISBN 1879936127
  • SCSI Encyclopedia Phases & Protocols A-M & N-Z (Set of two) - ENDL Publications 1991, ISBN 1879936100
• Mike Jackson: SAS Storage Architecture: Serial Attached SCSI – MindShare Press 2006, ISBN 0977087808

Example chapters and index PDF

• Fujitsu Corp.: [Fast Track To SCSI - Product Guide] - 1989

Actually a technical sales document if a bit long at 377 pages, and outdated but does contain loads of relevant SCSI information to a point where some implementations point to this publication rather than the published standard. There were later editions released by the company but they are not to be found on the net.

• L. Brett Glass: The SCSI Book - Brady 1991, ISBN 0-13-792136-5

Very good in its day and still has some value, but outdated.

Standards

• SCSI Primary Commands - 2 - Version 20
• SCSI Block Commands - 2 - Draft version
• [SCSI/ATA Translation - 2] - Draft version

Hardware reference texts

• Understanding the Single-Ended SCSI Bus - Microsemi application note

Fibre Channel

• Ralph O. Weber and Jeffrey D. Stai: FCBR-2: Fibre Channel Bench Reference, Second Edition - ENDL Publications 2005, ISBN 1879936186

Infiniband

• William T. Futral: InfiniBand Architecture Development and Deployment - Intel Press 2001, ISBN 0970284667
• Mellanox Technologies: Introduction to InfiniBand - PDF file

USB Attached SCSI

• Curtis E. Stevens: USB Attached SCSI Protocol - Presentation that gives an overview of the UASP.
• Universal Serial Bus Mass Storage Class Specification Overview - Gives you an overview of the standard including UAS.

UFS

• Introduction to the Universal Flash Storage Association - UFS Association white paper - has background info on UFS.
• UFS Standards - From JDEC

Links

• The T10 Committee - Oversees the SCSI standard.
• SCSI Trade Association - Promotes the SCSI standards.
• A mirror of an old Adaptec ftp site with lots of info - Since deleted from the Adaptec site proper.