RSX-15
| Industry | Computer hardware |
|---|---|
| Founded | 1957 |
| Founder | Ken Olsen, Harlan Anderson |
| Defunct | 1998 |
| Headquarters | Maynard, Massachusetts , United States |
| Products | PDP-15, PDP-1, PDP-4, PDP-7, PDP-9, PDP-11 |
The PDP-15 was an 18-bit minicomputer developed by Digital Equipment Corporation, first delivered in February 1970. It represented the fifth and final iteration in DEC's series of 18-bit machines, which began with the PDP-1 in 1959. Within its initial eight months on the market, more than 400 units were purchased. A subsequent model, the PDP-15/76, incorporated a full PDP-11, allowing it to utilize the widely adopted Unibus peripherals associated with the PDP-11. Production ceased in 1979, with total sales reaching approximately 790 units.
Essentially a modernized successor to the PDP-9, the PDP-15 was constructed using small-scale integration integrated circuit technology rather than the discrete transistor flip chips found in its predecessor. This advancement resulted in a more compact and cost-effective system: whereas an 8 kW PDP-9 was priced around $35,000 in 1968, a 4 kW PDP-15 was offered at $15,600 in 1970. A fully outfitted PDP-15 configuration—including 8 kW memory, punch tape, a KSR-35 terminal, a math coprocessor, and dual DECtape drives—cost $36,000, substantially less than earlier models.
The PDP-15 accommodated various operating systems such as DECsys, RSX-15, and DOS-15. It also featured compilers for programming languages like Fortran and ALGOL, broadening its applicability for scientific and commercial purposes.
History
Prior to the PDP-15, DEC produced several 18-bit systems including the PDP-1, PDP-4, PDP-7, and PDP-9. The last PDP-15 unit rolled off production lines in 1979.
Hardware
The PDP-15 stood out as DEC’s sole 18-bit computer built with TTL integrated circuits instead of individual transistors. Consistent with all DEC 18-bit models, it could be equipped with:
- an optional X-Y (point plotting or vector graphics) display,
- a hardware option for floating-point operations that improved speed by a factor of ten,
- core memory expandable up to 128K words.
Models
DEC released multiple versions of the PDP-15:
- PDP-15/10: Paper-tape-based system with 4K words
- PDP-15/20: Featured 8K words plus added DECtape
- PDP-15/30: Offered 16K words of memory along with memory protection and a foreground/background monitor
- PDP-15/35: Included a fixed-head disk drive with 524K words capacity
- PDP-15/40: Equipped with 24K words of memory
- PDP-15/50: Known for higher maintenance costs; some units remained operational into the early 1980s
PDP-15/76
This model combined the capabilities of the 15/40 with a front-end processor based on a PDP-11, forming a dual-processor configuration that shared memory with an attached PDP-11/05. The PDP-11 functioned as a peripheral processor, enabling access to Unibus peripherals.
Software
DEC provided several operating systems for the PDP-15 including DECsys, RSX-15, and XVM/RSX. Additionally, BOSS-15 (Batch Operating Software System), a batch processing monitor, was available.
DECsys
DECsys was the first mass-storage operating system offered by DEC for the PDP-15. It was an interactive single-user environment distributed on DECtape reels. Each user received their own copy to save programs and data, while a second DECtape served as temporary storage for assembling code and compiling Fortran programs.
RSX-15
Introduced by DEC in 1971, RSX-15 was primarily developed by Dennis "Dan" Brevik. Following the release of XVM/RSX, users could upgrade their RSX systems to XVM by adding the XM15 memory processor.
The operating system RSX-11 originated from porting RSX-15 to the PDP-11 platform but later developed independently with distinct design and features.
RSX-15 Name Origin
The system was initially designated DEX-15 by Brevik, an acronym for "Digital's Executive - for the PDP-15." However, due to trademark complications, a new name was necessary. Brevik experimented with various acronyms emphasizing key letters such as "X." After consultation with marketing director Bob Decker, the name "RSX" was selected. It originally stood for "Real-Time System Executive," but was later updated to mean "Resource Sharing Executive." This naming decision took place on the third floor of building 5 within DEC’s former mill facility.
XVM/RSX
Subsequent versions of the PDP-15 incorporated XVM/RSX, a multi-user real-time operating system that evolved from RSX-15. The XVM enhancement supported up to six simultaneous teletype terminals and was compatible with the PDP-15/76 model equipped with RK05 disk drives.
Non-DEC Software
The MUMPS operating system, created in 1966 on a PDP-7 outside of DEC, was also made available for use on the PDP-15.
Application Software
DEC provided a range of software packages for the PDP-15, covering mathematical, scientific, and business applications. Among these was a Commercial Subroutine Package designed to be compatible with the IBM 1130 system.