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TOPS-20
Company/
developer		 Digital Equipment Corporation
OS family DEC OS family
Source model  ?
Latest stable release  ? / ?
Marketing target  ?
Available language(s) Assembler, BLISS, FORTRAN, BASIC-20, et al
Update method  ?
Package manager  ?
Supported platforms PDP-10
Kernel type  ?
Default user interface Command line interface
License Proprietary
Working state Discontinued

The TOPS-20 operating system by Digital Equipment Corporation (DEC) was the second proprietary OS for the PDP-10. The software industry comprises businesses involved in the development, maintenance and publication of Computer software. A software developer is a person or organization concerned with facets of the software development process wider than design and coding a somewhat broader scope of Digital Equipment Corporation was a pioneering American company in the Computer industry In the Philosophy of language, a natural language (or ordinary language) is a Language that is spoken or written in phonemic-alphabetic or phonemically-related See the terminology section below for information regarding inconsistent use of the terms assembly and assembler BLISS is a System programming language developed at Carnegie Mellon University by W Fortran (previously FORTRAN) is a general-purpose, procedural, imperative Programming language that is especially suited to In Computer programming, BASIC (an Acronym for Beginner's All-purpose Symbolic Instruction Code) is a family of High-level programming languages The PDP-10 was a Mainframe computer manufactured by Digital Equipment Corporation (DEC from the late 1960s on the name stands for "Programmed Data Processor In Computer science, the kernel is the central component of most computer Operating systems (OS The user interface (or Human Computer Interface) is the aggregate of means by which people&mdash the users '&mdash interact with the System A software license (or software licence in commonwealth usage is a Legal instrument governing the usage or redistribution of copyright protected software Proprietary software is Computer software on which the producer has set restrictions on use private modification copying, or republishing. An operating system (commonly abbreviated OS and O/S) is the software component of a Computer system that is responsible for the management and coordination Digital Equipment Corporation was a pioneering American company in the Computer industry The PDP-10 was a Mainframe computer manufactured by Digital Equipment Corporation (DEC from the late 1960s on the name stands for "Programmed Data Processor It was preferred by most PDP-10 users over TOPS-10 (at least by those who were not ITS or WAITS partisans). ITS, the Incompatible Timesharing System (named in comparison with the Compatible Time-Sharing System also in use at MIT was an early revolutionary and influential WAITS was a heavily-modified variant of Digital Equipment Corporation 's Monitor Operating system (later renamed to and better known as TOPS-10) for the TOPS-20 began in 1969 as Bolt, Beranek and Newman's TENEX operating system, using special paging hardware. Year 1969 ( MCMLXIX) was a Common year starting on Wednesday (link will display full calendar of the Gregorian calendar. The system is almost entirely unrelated to the similarly-named TOPS-10 but shipped with the PA1050 TOPS-10 Monitor Calls emulation facility which allowed most, but not all, TOPS-10 executables to run unchanged. The TOPS-10 System was a computer Operating system from Digital Equipment Corporation (DEC for the PDP-10 released in 1964, the resulting systems As a matter of policy DEC did not update PA1050 to support later TOPS-10 additions except where required by DEC software.

Contents

TENEX

In the 1960s BBN was involved in a number of LISP-based artificial intelligence projects for DARPA, many of which had very large (for the era) memory requirements. The 1960s decade refers to the years from the beginning of 1960 to the end of 1969 Lisp (or LISP) is a family of Computer Programming languages with a long history and a distinctive fully parenthesized syntax The Defense Advanced Research Projects Agency (DARPA is an agency of the United States Department of Defense responsible for the development of new Technology One solution to this problem was to add paging software to the LISP language, allowing it to write out unused portions of memory to disk for later recall if needed. In Computer Operating systems that have their Main memory divided into pages, paging (sometimes called swapping) is a transfer Lisp (or LISP) is a family of Computer Programming languages with a long history and a distinctive fully parenthesized syntax One such system had been developed for the PDP-1 at MIT by Daniel Murphy before he joined BBN. The PDP-1 ( P rogrammed D ata P rocessor- 1) was the first Computer in Digital Equipment Corporation 's Daniel L Murphy is one of the architects of the TENEX operating system developed at Bolt Beranek and Newman in the 1970s Early DEC machines were based on an 18-bit word, allowing addresses to encode for a 262kword memory. Digital Equipment Corporation was a pioneering American company in the Computer industry Possibly the most well-known 18-bit computer architectures are the PDP-1, PDP-4, PDP-7, PDP-9 and PDP-15 Minicomputers produced The machines were based on expensive core memory and included nowhere near the required amount. Magnetic core memory, or ferrite-core memory, is an early form of Random access Computer memory. The pager used the otherwise unused bits of the address to store a key into a table of blocks on a magnetic drum that acted as the pager's backing store, and the software would fetch the pages if needed and then re-write the address to point to the proper area of RAM. Drum memory is a magnetic Data storage device and was an early form of Computer memory widely used in the 1950s and into the 1960s invented by Gustav Tauschek

In 1964 DEC announced the PDP-6. The PDP-6 ( P rogrammed D ata P rocessor- 6) was a Computer model developed by Digital Equipment Corporation (DEC DEC was still heavily involved with MIT's AI Lab, and many feature requests from the LISP hackers were moved into this machine. BBN became interested in buying one for their AI work when they became available, but wanted DEC to add a hardware version of Murphy's pager directly into the system. With such an addition, every program on the system would have paging support invisibly, making it much easier to do any sort of programming on the machine. DEC was initially interested, but soon (1966) announced they were in fact dropping the PDP-6 and concentrating solely on their smaller 18-bit and new 16-bit lines. The PDP-6 was expensive and complex, and had not sold well for these reasons.

It wasn't long until it became clear that DEC was once again entering the 36-bit business with what would become the PDP-10. Many early computers aimed at the scientific market had a 36- Bit word length. The PDP-10 was a Mainframe computer manufactured by Digital Equipment Corporation (DEC from the late 1960s on the name stands for "Programmed Data Processor BBN started talks with DEC to get a paging subsystem in the new machine, then known by its CPU name, the KA-10. DEC was not terribly interested. However, one development of these talks was the inclusion of two dual memory areas, allowing all programs to be divided into a protected (exec in DEC-speak) portion and a user portion. Additionally, DEC was firm on keeping the cost of the machine as low as possible, including only 16K words of core and placing registers in RAM, resulting in a considerable performance decrease. In Computer architecture, a processor register is a small amount of storage available on the CPU whose contents can be accessed more quickly than storage

BBN nevertheless went ahead with its purchase of several PDP-10s, and decided to build their own hardware pager. During this period a debate began on what operating system to run on the new machines. Strong arguments were made for the continued use of TOPS-10, in order to keep their existing software running with minimum effort. This would require a re-write of TOPS to support the paging system, and this seemed like a major problem. At the same time, TOPS did not support a number of features the developers wanted. In the end they decided to make a new system, but include an emulation library that would allow it to run existing TOPS-10 software with minor effort.

The new system, soon known as TENEX, also included a full virtual memory system -- that is, not only could programs access a full 262kwords of memory, every program could do so at the same time. Virtual memory is a Computer system technique which gives an application program the impression that it has contiguous working memory while in fact it may be physically The pager system would handle mapping as it would always, copying data to and from the backing store as needed. The only change needed was for the pager to be able to hold several sets of mappings between RAM and store, one for each program using the system. The pager also held access time information in order to tune performance. The resulting pager was fairly complex, filling a full-height 19" rackmount chassis.

One notable feature of TENEX was its user-oriented command line interpreter. Unlike typical systems of the era, TENEX deliberately used long command names and even included noise words to further expand the commands for clarity. For instance, Unix uses ls to print a list of files in a directory, whereas TENEX used DIRECTORY (OF FILES). "DIRECTORY" was the command word, "(OF FILES)" was noise added to make the purpose of the command clearer. Of course users didn't want to type these long commands, so TENEX used an escape recognition system that would expand partial command words into completed words or phrases. Command line completion is a common feature of Command line interpreters in which the program automatically fills in partially typed tokens For instance, the user could type DIR and the escape key, at which point TENEX would replace DIR with the full command. The same feature worked with file names, which took some effort on the part of the interpreter, and the system allowed for long file names with human-readable descriptions. TENEX also included a help system that could be invoked by typing the question mark (?), which would print out a list of possible matching commands and then return the user to the command line with the question mark removed.

TENEX became fairly popular in the small PDP-10 market, and the external pager hardware developed into a small business of its own. In early 1970 DEC started work on an upgrade to the PDP-10 processor, the KI-10. BBN once again attempted to get DEC to support a full hardware paging system, but instead DEC decided on a much simpler system. This plan eventually backfired; by this point TENEX was one of the most popular PDP-10 operating systems, and it would not run on the new machines. Known as the DECsystem-10 in the marketplace, the normal operating system was TOPS-10, which did not include any sort of virtual memory system.

TOPS-20

Learning from this mistake, the DEC sales manager in charge of the PDP-10 line managed to purchase the rights to TENEX from BBN and set up a project to port it to the new machine. At around this time Murphy moved from BBN to DEC as well, helping on the porting project. Most of the work centered on emulating the BBN pager hardware in a combination of software and the KI-10's simpler hardware. The speed of the KI-10 compared to the PDP-6 made this possible. Additionally the porting effort required a number of new device drivers to support the newer backing store devices being used. In computing a device driver or software driver is a Computer program allowing higher-level computer programs to interact with a Hardware device

Just as the new TENEX was shipping, DEC started work on the KL-10, intended to be a low-cost version of the KI-10. While this was going on, Stanford University AI-programmers, many of them MIT alumni, were working on their own project to build a PDP-10 that was ten times faster than the original KA-10's. Leland Stanford Junior University, commonly known as Stanford University or simply Stanford, is a private Research university located in DEC visited them and many of their ideas were then folded into the KL-10 project. The same year IBM also announced their own machine with virtual memory, making it a standard requirement for any computer. In the end the KL integrated a number of major changes to the system, but did not end up being any lower in cost. From the start, the new DECSYSTEM-20 would run a version of TENEX as its default operating system. The DECSYSTEM-20 was a 36-bit DEC PDP-10 Computer running the TOPS-20 operating system

Extensions for the new machine were limited, but difficult. The main upgrade was the addition of extended addressing, which allowed the machine to support a 23-bit address space. The extra addressing bits were "added" by the pager hardware, which was now implemented in microcode. Microprogramming (ie writing microcode) is a method that can be employed to implement Machine instructions in a CPU relatively easily often using less The extra bits allowed multiple pages to be mapped into the same physical hardware, which also allowed the system to support a wider range of RAM without it being "obvious". For backward compatibility, the machine included instructions that could generate 18-bit addresses on demand. In Technology, especially Computing (irrespective of platform a product is said to be backward compatible when it is able to take the place of an older product

The first in-house code name for the operating system was VIROS (VIRtual memory Operating System); when customers started asking questions, the name was changed to SNARK so that DEC could truthfully deny that there was any project called VIROS. When the name SNARK became known, the name was briefly reversed to become KRANS; this was quickly abandoned when someone objected that "krans" meant "funeral wreath" in Swedish (though it simply means "wreath"; this part of the story may be apocryphal). Swedish ( is a North Germanic language spoken by more than nine million people predominantly in Sweden and parts of Finland, especially along the

Ultimately DEC picked TOPS-20 as the name of the operating system, and it was as TOPS-20 that it was marketed. The hacker community, mindful of its origins, quickly dubbed it TWENEX (a contraction of "twenty TENEX"), even though by this point very little of the original TENEX code remained (analogously to the differences between AT&T V7 Unix and BSD). Before proposing a merge request please see Talk and see if the merger you propose has recently been made and DEC people cringed when they heard "TWENEX", but the term caught on nevertheless (the written abbreviation "20x" was also used).

TWENEX was successful and very popular; in fact, there was a period in the early 1980s when it commanded as fervent a culture of partisans as Unix or ITS - but DEC's decision to scrap all the internal rivals to the VAX architecture and its VMS OS killed the DEC-20 and put an end to TWENEX's brief period of popularity. The 1980s was the decade spanning from January 1 1980 to December 31 1989. Unix (officially trademarked as UNIX, sometimes also written as Unix with Small caps) is a computer Name "VAX" was originally an Acronym for V irtual A ddress e' X' tension, both because the VAX was seen as a 32-bit Open Virtual Memory System ( OpenVMS) initially known just as Virtual Memory System ( VMS) is the name of a High-end Computer server DEC attempted to convince TOPS-20 users to convert to VMS, but instead, by the late 1980s, most of the TOPS-20 hackers had migrated to Unix. The 1980s was the decade spanning from January 1 1980 to December 31 1989.

Source

References

External links

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