TYMCOM-X

<operating system>

Tymshare's operating system which ran for many years on Tymshare's PDP-10s. It was a descendent of TOPS-10 but had many of the important features of TOPS-20 such as real paging and controllable/spawnable processes. TYMCOM-X, one of the best kept secrets in the PDP-10 folklore, was written by Bill Weiher, Vance Socci <[email protected]>, Allen Ginzburg, Karen Kolling, Art Atkinson, Gary Morgenthaler (founder of the company that produced IDRIS), Todd Corenson and Murray Bowles. Some copies still run today. Most TYMNET development was done under TYMCOM-X and Tymshare sold a TYMCOM-X system to TRW to use in their credit reporting network, which was based on a purchased copy of TYMNET circa 1979.

[E-mail from Vance Socci 1994-05-20].

Last updated: 1995-11-09

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TYMNET

<networking, history>

A United States-wide commercial computer network, created by Tymshare, Inc. some time before 1970, and used for remote login and file transfer. The network public went live in November 1971.

In its original implementation, it consisted of fairly simple circuit-oriented nodes, whose circuits were created by central network supervisors writing into the appropriate nodes' "permuter tables". The supervisors also performed login validations as well as circuit management. Circuits were character oriented and the network was oriented toward interactive character-by-character full-duplex communications circuits.

The network had more than one supervisor running, but only one was active, the others being put to sleep with "sleeping pill" messages. If the active supervisor went down, all the others would wake up and battle for control of the network. After the battle, the supervisor with the highest pre-set priority would dominate, and the network would then again be controlled by only one supervisor. (During the takeover battle, the net consisted of subsets of itself across which new circuits could not be built). Existing circuits were not affected by supervisor switches.

There was a clever scheme to switch the echoing function between the local node and the host based on whether or not a special character had been typed by the user. Data transfers were also possible via "auxiliary circuits".

The Tymshare hosts (which ran customer code) were SDS 940, DEC PDP-10, and eventually IBM 370 computers. Xerox XDS 940 might have been used if Xerox, who bought the design for the SDS 940 from Scientific Data Systems, had ever built any.

The switches were originally Varian Data Machines 620i. The Interdata 8/32 was never used because the performance was disappointing. The TYMNET Engine, based loosely on the Interdata 7/32, was developed instead to replace the Varian 620i. In the early 1990s, newer "Turbo" nodes based on the Motorola 68000 began to replace the 7/32s. These were later replaced with SPARCs.

PDP-10s supported (and still do in 1999) cross-platform development and billing.

Tymshare, Inc. originally wrote and implemented TYMNET to provide nationwide access for their time-sharing customers.

La Roy Tymes booted up the public TYMNET in November of 1971 and, as of March 2002, it had been running ever since without a single system crash.

TYMNET was the largest commercial network in the United States in its heyday, with nodes in every major US city and a few overseas as well. Tymshare acquired a French subsidiary, SLIGOS, and had TYMNET nodes in Paris, France.

Tymshare sold the TYMNET network software to TRW, who created their own private network (which was not called TYMNET). In about 1979, TYMNET Inc. was spun off from Tymshare, Inc. to continue administration and development of the network.

TYMNET outlived its parent company Tymshare and was acquired by MCI. As of May 1994 they still ran three DEC KL-10s under TYMCOM-X, although they planned to decommission them soon.

The original creators of TYMNET included: Ann Hardy, Norm Hardy, Bill Frantz. La Roy Tymes (who always insisted that his name was NOT the source of the name) wrote the first supervisor which ran on the 940. Joe Rinde made many significant technical and marketing contributions. La Roy wrote most of the code of the network proper. Several others wrote code in support of development and administration. Just recently (1999) La Roy, on contract, wrote a version of the supervisor to run on SPARC hardware.

The name TYMNET was suggested by Vigril Swearingen in a weekly meeting between Tymshare technical and marketing staff in about 1970.

http://cap-lore.com/ETH.html.

[E-mail from La Roy Tymes]

Last updated: 2002-11-26

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Tymshare, Inc.

<company>

The US company that created the TYMNET network.

Last updated: 1999-03-17

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type

<theory, programming>

(Or "data type") A set of values from which a variable, constant, function, or other expression may take its value. A type is a classification of data that tells the compiler or interpreter how the programmer intends to use it. For example, the process and result of adding two variables differs greatly according to whether they are integers, floating point numbers, or strings.

Types supported by most programming languages include integers (usually limited to some range so they will fit in one word of storage), Booleans, floating point numbers, and characters. Strings are also common, and are represented as lists of characters in some languages.

If s and t are types, then so is s -> t, the type of functions from s to t; that is, give them a term of type s, functions of type s -> t will return a term of type t.

Some types are primitive - built-in to the language, with no visible internal structure - e.g. Boolean; others are composite - constructed from one or more other types (of either kind) - e.g. lists, arrays, structures, unions. Object-oriented programming extends this with classes which encapsulate both the structure of a type and the operations that can be performed on it.

Some languages provide strong typing, others allow implicit type conversion and/or explicit type conversion.

Last updated: 2003-12-22

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type-ahead

<operating system>

The facility where the user can type more characters before the system has fully responded to those already typed. Type-ahead is common on most current systems. It allows the user to type without worrying that the computer may miss input because it is temporarily busy, e.g. reformating a page, checking spelling, or simply suffering from network latency. There is usually some limit to the amount of input the system can buffer, beyond which it will lose input.

[Equivalent term for speech recognition?]

Last updated: 2003-06-15

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type-ahead search

incremental search

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type assignment

<theory>

A mapping of the free variables of some expression E to types. This is used in type inference to deduce the type of E and its subexpressions.

Last updated: 2002-02-22

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type class

A set of types for which certain operations or methods are defined. E.g. the class Number might have methods for addition and subtraction. Classes are a feature of object oriented languages and of the functional programming language Haskell. See also inheritance.

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typed lambda-calculus

<theory>

(TLC) A variety of lambda-calculus in which every term is labelled with a type.

A function application (A B) is only synctactically valid if A has type s --> t, where the type of B is s (or an instance or s in a polymorphic language) and t is any type.

If the types allowed for terms are restricted, e.g. to Hindley-Milner types then no term may be applied to itself, thus avoiding one kind of non-terminating evaluation.

Most functional programming languages, e.g. Haskell, ML, are closely based on variants of the typed lambda-calculus.

Last updated: 1995-03-25

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TypedProlog

<language>

A strongly typed logic programming language.

Last updated: 1995-03-25

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typeface

<text>

The style or design of a font. Other independent parameters are size, boldness (thickness of lines), and obliqueness (a sheer transformation applied to the characters, not to be confused with a specifically designed italic font).

Last updated: 1996-08-02

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type inference

<programming>

An algorithm for ascribing types to expressions in some language, based on the types of the constants of the language and a set of type inference rules such as

	f :: A -> B,  x :: A
	---------------------  (App)
	      f x :: B

This rule, called "App" for application, says that if expression f has type A -> B and expression x has type A then we can deduce that expression (f x) has type B. The expressions above the line are the premises and below, the conclusion. An alternative notation often used is:

	G |- x : A

where "|-" is the turnstile symbol (LaTeX \vdash) and G is a type assignment for the free variables of expression x. The above can be read "under assumptions G, expression x has type A". (As in Haskell, we use a double "::" for type declarations and a single ":" for the infix list constructor, cons).

Given an expression

	plus (head l) 1

we can label each subexpression with a type, using type variables X, Y, etc. for unknown types:

	(plus :: Int -> Int -> Int)
		(((head :: [a] -> a) (l :: Y)) :: X)
		(1 :: Int)

We then use unification on type variables to match the partial application of plus to its first argument against the App rule, yielding a type (Int -> Int) and a substitution X = Int. Re-using App for the application to the second argument gives an overall type Int and no further substitutions. Similarly, matching App against the application (head l) we get Y = [X]. We already know X = Int so therefore Y = [Int].

This process is used both to infer types for expressions and to check that any types given by the user are consistent.

See also generic type variable, principal type.

Last updated: 1995-02-03

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type scheme

A typing of an expression which may include type variables. E.g.

	\ x . x :: a -> a

where a is a generic type variable which may be instantiated to any type.

Last updated: 1994-10-31

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typo

typographical error

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typographical error

(typo) An error while inputting text via keyboard, made despite the fact that the user knows exactly what to type in. This usually results from the operator's inexperience at keyboarding, rushing, not paying attention, or carelessness.

Compare: mouso, thinko.

Last updated: 1996-04-20

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TYPOL

<language>

A specialised logic programming language.

["TYPOL: A Formalism to Implement Natural Semantics", T. Despeyroux, RR 94, INRIA, 1988].

Last updated: 1994-10-31

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typo squatter

<web>

A domain squatter who registers a domain name that is a common typographical error for a popular website so that people will visit their site accidentally, e.g. http://goggle.com/ for http://google.com/.

Last updated: 2007-07-13

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tyt

<chat>

Take your time.

Last updated: 2004-02-15

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typographical errorTYPOLtypo squattertytTZtzuaUAN

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