• PF50 Multiprocessing Option
• Sparse Programs (GEORGE4)
• Running G4 programs under G3
• The FPC FP6000
• PF50 and Paging!
• The Evolution of 1900 FPUs
• The 1900 Multiprocessing Options
• Monitor Modes
• Priority/Real-time Mode
• The GD1830 GPVDU
• The GD1831 IDU
• Executive Summaries
• Consolidators
• Updating 1900 PASCAL
• Coding for PF56 in PASCAL
• The case of the missing Communications Controller

ICL 1900 Mystery and Unexpected Items

Here is a collection of items and questions that have arisen during the development of the emulators. Subjects include: -

1. Things that we found out that were different to the user facing manuals.
2. Things that we had no idea existed.
   1. Priority Mode or Realtime Mode - Turns out that the larger 1900s all supported it and that the 1900 wasn't a two-mode machine (OBJECT & EXECUTIVE) but had a third mode PRIORITY MODE (PMODE) which given the right peripherals allowed both OBJECT and EXEC modes to be interrupted - three modes.
   2. A Paging option was considered for the 1902A .. 1902T series.The basic PF-50 CPU design included a bit assiged in the Interrupt Register for page-fault traps. Can only guess that the PF-50 performance under GEORGE 4 might not have been too impressive.
   3. Again, on the PF-50, there were interrupt bits set aside for a dual-CPU version.
3. Things that ICT/ICL had stated were not possible or had been removed (but weren't).
   1. The so-called Monitor Modes. Somewhat comparable to the Trace-Trap of the later pdp-11 machines. Only supported on some of the earlier executives (E4BM, E6BM). The early compilers and assemblers used these facilities.
4. Things that we just tried - "just to see what would happen".
   1. Running George 4 FORTRAN and Algol compilers (XFIH and XALH) on a George 3 system. Also running XPCH consolidator and being able to run the resulting images.
5. Unknown peripherals: - Does anyone have anything on these?
   1. A previously unknown interactive graphics VDU with light-pen, the GD1830, only known as we had an EWG3 exec package (driver) for it. We created an emulator as we had some test programs for it on an engineer's tape. Quite recently we obtained a user manual for these devices, which answered many, but not all of our questions.
   2. A device (the IDU) that supports up to 8 or 64 small CRTs and a minimal keyboard . - We have what could be an exec package for this, but no software.
   3. A Curve Tracer (*CO ?) - Exec package in EWG3, but we have neither software nor a description of the PERIs.
   4. Peripheral Tester (*PS ?) Allowed simple read/write PERI instructions to be issued to a channel.
   5. The DataDisk disc storage device. - This was certainly a strange device. A disc device, but neither BDAS nor UDAS, it has 60-word blocks and 16 character filenames. We have a number of *DS disc management programs for this, but no exec packages. It is not possible to create an exec package for this based on E4BM as the E4BM version that we have is Mk3; Mk4 is required to support any form of random-access device (discs, drums, MCF or *DS).
6. The 1906 and 1907 we have no detailed information about at all. Does anyone have anything regarding these high-end 1900 machines?