DECSYSTEM-20
| Company type | Computer series |
|---|---|
| Industry | Computer hardware |
| Predecessor | DECsystem-10 |
| Founded | 1977 |
| Products | Mainframe computers (DECSYSTEM-2020, 2040, 2050, 2060, 2065) |
| Owner | Digital Equipment Corporation |
The DECSYSTEM-20 series consisted of 36-bit Digital Equipment Corporation PDP-10 mainframe computers that operated on the TOPS-20 operating system. This line was launched in 1977.
To distinguish from the PDP-11, PDP-10 machines running the TOPS-10 OS were branded as DECsystem-10. In contrast, systems equipped with KL10 processors and running TOPS-20 were identified as DECSYSTEM-20—the uppercase naming arose due to legal action by Singer Corporation, makers of the System Ten. Occasionally, the DECSYSTEM-20 was informally referred to as PDP-20, although DEC itself never adopted this term.
Models
The available models encompassed:
- DECSYSTEM-2020: Featuring a KS10 bit-slice CPU and supporting up to 512 kilowords of solid state RAM (the ADP OnSite variant extended this to 1 MW)
- DECSYSTEM-2040: Utilizing a KL10 ECL processor with magnetic core memory up to 1024 kilowords
- DECSYSTEM-2050: Incorporating a KL10 ECL CPU, equipped with a 2k word cache and up to 1024 kilowords of RAM
- DECSYSTEM-2060: Employing a KL10 ECL processor with a 2k word cache and solid state memory reaching 4096 kilowords
- DECSYSTEM-2065: An enhanced DECSYSTEM-2060 model featuring an MCA25 pager, which provided a double-sized two-way associative hardware page table
A key user-facing distinction between DECsystem-10 and DECSYSTEM-20 systems was their operating system and chassis coloration: TOPS-10 machines typically displayed "Blasi Blue" paint, whereas TOPS-20 units were finished in "Terracotta."
From an internal perspective, earlier KL10 Model A processors found in DECsystem-10 featured an external memory bus and taller cabinets. Later KL10 Model B processors used in DECSYSTEM-20 integrated memory directly into the CPU cabinet, resulting in shorter enclosure heights.
The final implementation of DEC’s 36-bit architecture was embodied by the single-cabinet DECSYSTEM-2020, which utilized the KS10 processor.
Primarily intended as compact mainframes for timesharing, the DECSYSTEM-20 allowed multiple users to log in simultaneously, compile code, and execute programs. The operating system ensured distinct disk space allocation and user access controls. For instance, a model 2060 could accommodate between 40 and 60 concurrent users before experiencing noticeable performance decline.
Remaining machines
The Living Computer Museum in Seattle operates a functional 2065 running TOPS-10, which can be accessed remotely via SSH free of charge after registration.
Trivia
On 1 May 1978, the first instance of email spam promoted the DECSYSTEM-20 to ARPANET users located on the west coast.
References
- C. Gordon Bell, Alan Kotok, Thomas N. Hasting, Richard Hill, "The Evolution of the DECsystem-10", in C. Gordon Bell et al., Computer Engineering: A DEC View of Hardware Systems Design (Digital Equipment, Bedford, 1979)
- Frank da Cruz, Christine Gianone, The DECSYSTEM-20 at Columbia University 1977–1988
Further reading
- Storage Organization and Management in TENEX, Daniel L. Murphy, AFIPS Proceedings, 1972 FJCC
- "DECsystem-10/DECSYSTEM-20 Processor Reference Manual", 1982
- "Manuals for DEC 36-bit computers"
- "Introduction to DECSYSTEM-20 Assembly Language Programming" (Ralph E. Gorin, 1981, )
External links
- Comprehensive summary of KL-10 variants
- Columbia University's DECSYSTEM-20 information
- Access to the Living Computer Museum, gateway to the Paul Allen archive featuring a functioning DECSYSTEM-20 KL-10 2065 system