The TOPS-20

operating system An operating system (OS) is system software that manages computer hardware, software resources, and provides common daemon (computing), services for computer programs. Time-sharing operating systems scheduler (computing), schedule tasks for ef ...

Digital Equipment Corporation Digital Equipment Corporation (DEC ), using the trademark Digital, was a major American company in the computer industry from the 1960s to the 1990s. The company was co-founded by Ken Olsen and Harlan Anderson in 1957. Olsen was president un ...

(DEC) is a proprietary OS used on some of DEC's 36-bit

mainframe computer A mainframe computer, informally called a mainframe or big iron, is a computer used primarily by large organizations for critical applications like bulk data processing for tasks such as censuses, industry and consumer statistics, enterprise ...

s. The Hardware Reference Manual was described as for "DECsystem-10/DECSYSTEM-20 Processor" (meaning the DEC

PDP-10 Digital Equipment Corporation (DEC)'s PDP-10, later marketed as the DECsystem-10, is a mainframe computer family manufactured beginning in 1966 and discontinued in 1983. 1970s models and beyond were marketed under the DECsystem-10 name, espec ...

and the DECSYSTEM-20). TOPS-20 began in 1969 as the TENEX operating system of Bolt, Beranek and Newman (BBN) and shipped as a product by DEC starting in 1976. TOPS-20 is almost entirely unrelated to the similarly named

TOPS-10 TOPS-10 System (''Timesharing / Total Operating System-10'') is a discontinued operating system from Digital Equipment Corporation (DEC) for the PDP-10 (or DECsystem-10) mainframe computer family. Launched in 1967, TOPS-10 evolved from the earlie ...

, but it was shipped with the PA1050 TOPS-10 Monitor Calls emulation facility which allowed most, but not all, TOPS-10 executables to run unchanged. As a matter of policy, DEC did not update PA1050 to support later TOPS-10 additions except where required by DEC software. TOPS-20 competed with TOPS-10, ITS and WAITS—all of which were notable time-sharing systems for the

during this timeframe.

TENEX

TOPS-20 was based upon the TENEX operating system, which had been created by Bolt Beranek and Newman for Digital's

computer. After Digital started development of the KI-10 version of the PDP-10, an issue arose: by this point TENEX was the most popular customer-written PDP-10 operating systems, but it would not run on the new, faster KI-10s. To correct this problem, the DEC PDP-10 sales manager purchased the rights to TENEX from BBN and set up a project to port it to the new machine. In the end, very little of the original TENEX code remained, and Digital ultimately named the resulting operating system TOPS-20.

PA1050

Some of what came with TOPS-20 was merely an emulation of the

Operating System's calls. These were known as UUO's, standing for Unimplemented User Operation, and were needed both for compilers, which were not 20-specific, to run, as well as user-programs written in these languages. The package that was mapped into a user's address space was named PA1050: PA as in PAT as in compatibility; 10 as in DEC or PDP 10; 50 as in a PDP 10 Model 50, 10/50, 1050.The 10/50 was the top-of-the-line KA machine at that time. The family continued with another KA, the 10/55, and then came KI, KL & KS. Sometimes PA1050 was referred to as PAT, a name that was a good fit to the fact that PA1050, "was simply unprivileged user-mode code" that "performed the requested action, using JSYS calls where necessary."

TOPS-20 capabilities

The major ways to get at TOPS-20 capabilities, and what made TOPS-20 important, were * Commands entered via the command processor, EXEC.EXE * JSYS (Jump to System) calls from MACro-language (.MAC) programs The "EXEC" accomplished its work primarily using * internal code, including calls via JSYS * requesting services from "GALAXY" components (e.g. spoolers)

Command processor

Rather advanced for its day were some TOPS-20-specific features: * Command completion * Dynamic help in the form of :*''noise-words'' - typing DIR and then pressing the ESCape key resulted in ::::DIRectory (of files) ::typing and pressing the key resulted in :::: Information (about) One could then type to find out what operands were permitted/required. Pressing displays status information.

Commands

The following list of commands are supported by the TOPS-20 Command Processor. * ACCESS * ADVISE * APPEND * ARCHIVE * ASSIGN * ATTACH * BACKSPACE * BLANK * BREAK * BUILD * CANCEL * CLOSE * COMPILE * CONNECT * CONTINUE * COPY * CREATE * CREF * CSAVE * DAYTIME * DDT * DEASSIGN *

DEBUG In computer programming and software development, debugging is the process of finding and resolving '' bugs'' (defects or problems that prevent correct operation) within computer programs, software, or systems. Debugging tactics can involve i ...

* DEFINE * DELETE * DEPOSIT * DETACH *

DIRECTORY Directory may refer to: * Directory (computing), or folder, a file system structure in which to store computer files * Directory (OpenVMS command) * Directory service, a software application for organizing information about a computer network' ...

* DISABLE * DISCARD * DISMOUNT * EDIT * ENABLE * END-ACCESS * EOF * ERUN * EXAMINE * EXECUTE * EXPUNGE * FDIRECTORY * FORK * FREEZE * GET *

HELP Help is a word meaning to give aid or signal distress. Help may refer to: Arts, entertainment, and media Films * ''Help'' (2010 film), a Bollywood horror film * ''Help'' (2021 theatrical film), a British psychological thriller film * '' ...

* INFORMATION * KEEP * LOAD * LOGIN * LOGOUT * MERGE * MODIFY *

MOUNT Mount is often used as part of the name of specific mountains, e.g. Mount Everest. Mount or Mounts may also refer to: Places * Mount, Cornwall, a village in Warleggan parish, England * Mount, Perranzabuloe, a hamlet in Perranzabuloe parish, ...

* PERUSE * PLOT * POP * PRINT * PUNCH * PUSH * R * RECEIVE * REENTER * REFUSE * REMARK *

RENAME Rename may refer to: * Rename (computing), rename of a file on a computer * RENAME (command), command to rename a file in various operating systems * Rename (relational algebra), unary operation in relational algebra * Company renaming, rename ...

* RESET * RETRIEVE * REWIND *

RUN Run(s) or RUN may refer to: Places * Run (island), one of the Banda Islands in Indonesia * Run (stream), a stream in the Dutch province of North Brabant People * Run (rapper), Joseph Simmons, now known as "Reverend Run", from the hip-hop group ...

* SAVE * SEND * SET * SET HOST * SKIP *

START Start can refer to multiple topics: *Takeoff, the phase of flight where an aircraft transitions from moving along the ground to flying through the air *Starting lineup in sports * Standing start, and rolling start, in an auto race Acronyms *S ...

* SUBMIT * SYSTAT * TAKE * TALK * TDIRECTORY * TERMINAL * TRANSLATE * TYPE * UNATTACH *

UNDELETE Undeletion is a feature for restoring computer files which have been removed from a file system by file deletion. Deleted data can be recovered on many file systems, but not all file systems provide an undeletion feature. Recovering data wit ...

* UNKEEP * UNLOAD * VDIRECTORY

JSYS features

JSYS stands for Jump to SYStem. Operands were at times memory addresses. "TOPS-20 allows you to use 18-bit or 30-bit addresses. Some monitor calls require one kind, some the other; some calls accept either kind. Some monitor calls use only 18 bits to hold an address. These calls interpret 18-bit addresses as locations in the current section." Internally, files were first identified, using a GTJFN (Get Job File Number) JSYS, and then that JFN number was used to open (OPENF) and manipulate the file's contents.

PCL (Programmable Command Language)

PCL (Programmable Command Language) is a programming language that runs under TOPS-20. PCL source programs are, by default, stored with Filetype .PCL, and enable extending the TOPS-20 EXEC via a verb named DECLARE. Newly compiled commands then become functionally part of the EXEC.

PCL language features

PCL includes: * flow control: DO While/Until, CASE/SELECT, IF-THEN-ELSE, GOTO * character string operations (length, substring, concatenation) * access to system information (date/time, file attributes, device characteristics)

TOPS-20 today

Paul Allen Paul Gardner Allen (January 21, 1953 – October 15, 2018) was an American business magnate, computer programmer, researcher, investor, and philanthropist. He co-founded Microsoft Corporation with childhood friend Bill Gates in 1975, whic ...

maintained several publicly accessible historic computer systems before his death, including an XKL TOAD-2 running TOPS-20. See also SDF Public Access Unix System.

References

*
DIGITAL Computing Timeline
.