|Theo Engel's P800 pages (Philips Electronics' 16 bit minicomputers)|
Last update: Dec 15 '11
About the P800 Minicomputers
After selling the Honeywell minicomputers for a number of years, Philips developed its own minicomputer line. This first resulted in the P880, which was a very powerful 16 bit machine, but it was for 1970/1971 a too big and too expensive machine for applications which required small scale, cost effective computer power. The alternative became another computer line, incompatible with the P880, but much more focused on minicomputer applications at that time. The P880 found its way to scientific and computer graphics applications.
P860 (rack mount)
P857 (rack mount)
In 1971, Philips Data Systems started the marketing of their 16 bit minicomputers of the P800 family (development name: Sagittaire and created by Philips-CTI in Fontenay Aux Roses near Paris, France). The family started with 3 models: P850, P855 and P860. The P850 was a very small machine with only 2k of 16 bit words. The P855 and P860, upwards compatible with the P850, shared a common instruction set and had a memory varying from 4k 16 bit words up to 32k 16 bit words. The only difference between the two models was performance: the P855 memory cycle time was 1.2 musec, while the memory cycle time of the P860 was 0.84 musec. End 1973 this difference was removed; the P855 got the performance of the P860 and the P860 was dropped.
The hardware was complemented with an extensive set of standard software: operating systems for various purposes, language processors, utilities, multi key file management and software libraries (for real time, non real time and data communication applications).
The standard software was delivered as "papertape" software for the smaller machines and disk oriented software for the larger machines. All standard software like the assembler, Fortran, linker, etc. were running under monitor control (except for the P850). BOM (Basic Operating Monitor) and BRTM (Basic Real Time Monitor) supported the papertape oriented configurations, while DOM (Disc Operating Monitor) and DRTM (Disk Real Time Monitor), both upwards compatible with BOM and BRTM, supported the machines configured with one or more disc units. These operating environments could be used on machines with a memory of up to 32k 16 bit words. In principle these systems were "single user systems", while the real time monitors supported multitasking.
With the P857, with memory up to 128 kwords, an additional operating system was introduced: MAS (Multi Application System). By combining the features of DOM (batch processing, software development, ..) and DRTM, this system created a foreground/background operating environment with true multi user support.
By means of a system generation process, each operating system could be composed to fit a machine configuration and the applications to run on that machine. This way also cassette tape and later floppy disc based systems could be produced. For small/dedicated process control applications, a special monitor was available: SRTM (Small Real Time Monitor), which supported a subset of the BRTM functionality.
Unfortunately not much is left of this computer family. Also on the web is hardly any reference available, so it looks like these machines are completely forgotten. When cleaning my archive I found a few P800 documents, which I once kept as remembrance to an early period in my working life. It is not much; most I had, already long time ago disappeared in that other archive. But the little I still have and remember and the documentation and software (both DOM and DRTM) I received since these pages were published (thank you !), is may be just enough to prevent that the P800 is completely lost for the community.
The P800 machines are a good illustration of where the development in the early seventies of small computers was heading at. Compared with the Honeywell machines the biggest difference was not the hardware cq. the size of the machines. Indeed, the P800's were much smaller than the DDP-416/DDP-516. But the H316 was also much smaller than its predecessors. The biggest difference, and also the beauty of the P800 machines at that time is, e.g. compared with the Honeywell machines, the instruction set: 16 general purpose registers, subroutine linkage by means of a hardware stack, standard an interrupt priority system, interrupt handling with a hardware stack, software interrupt in combination with user/system mode differentiation and memory protection to completely separate user applications and operating system and excellent facilities to make code reentrant. In a little more than 5 years, the ideas about the design of a small computer were completely changed. These pages are meant to preserve at least some of the ideas that were behind the 1970 P800 design.Documentation
P800 (P852/56/57 ..) Instruction Set (Extended Specification)
P856M/P857M System Handbook
P800 Disc Operating Monitor (DOM) for P852/56/57
P800 Disc Real Time Monitor (DRTM) for P852/56/57
Page last updated on: December 29 2008 | Contact: Info@theoengel.nl