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The '''Standard Tape Interconnect''' (usually referred to by the acronym, '''STI''') is a [[Digital Equipment Corporation|DEC]] designed [[magnetic tape]] [[magnetic tape controller|formatter]] to [[device controller|controller]] [[interface]] standard, intended to support sequential-type [[mass storage]] devices. It is a key element of the [[Digital Storage Architecture]] (DSA), used with [[PDP-11]]s and with [[VAX]] single and multiple [[Central Processing Unit|CPU]] systems.

STI claims to offer high performance, availability, and configuration flexibility, and does so across a large range of configurations (ranging from small individual systems, to groups of large [[server]]s.

A variant, the [[Standard Disk Interconnect]] (SDI), is used with [[disk]] systems. It shares its physical connection technology (called the [[Standard Drive Bus]], SDB) with STI; the higher layer [[protocol]]s are adapted to [[random access]] storage needs. STI configurations are slightly more complex than SDI, as SDI controllers connect directly to disk [[drive]]s, whereas in STI a formatter is interpolated between the STI controller and the [[magnetic tape drive]]s attached to it.

==Technical details==

The SDB formatter to controller interconnect is a [[serial]] link which connects each drive directly (i.e. individually), or 'radially' (a term for such a device connection approach which DEC also used in its early machines), to its controller.

Logically, at a higher layer, STI consists of a [[protocol]] by which a controller can recognize a drive's characteristics, direct its mechanical operation, store data on or retrieve data from it, and recognize and recover from error conditions. This protocol is the [[Tape Mass Storage Control Protocol]] (TMSCP).

STI commands include:

* Start and stop the motion of the tape
* Space the tape forward or backward
* Rewind the tape
* Write an inter-record gap on the tape
* Select a configurable attribute (e.g. density)
* Ask a drive for its attributes and/or status
* Begin recovery from an error

==STI Family of DSA Products==

The family of products which implement the STI includes:

* STI [[Hierarchical Storage Controller]]s (HSCs):
** [[HSC40]]
** [[HSC50 Mass-Storage Controller|HSC50]]
** [[HSC60]]
** [[HSC65]]
** [[HSC70]]
** [[HSC90]]
** [[HSC95]]

* STI drives
** [[TA78]]
** [[TA79]]
** [[TA81]]
** [[TA90]]

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==Further reading==

* ''Digital Storage Technology Handbook'', 1989 (EC-H0374-45/89) - see Chapter 4, The Digital Storage Interconnects
* ''Digital Large System Mass Storage Handbook'', 1986 - Chapter 7, The Storage Interconnect


[[Category: DEC Mass Storage]]
[[Category: DEC Buses]]
[[Category: DEC Interface Standards]]

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Standard Tape Interconnect - Revision history

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