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This document has been written in English for the following reasons:

- In the computerworld there are a lot of English (American) terms
  wich have a narrowly defined meaning. Normally these terms have
  no proper translation in Dutch
- A Dutch document with English terms is difficult to read and the
  resulting language would be difficult to pronounce, as you would
  have to switch from dutch pronounciation to english and back.
  Furthermore we do not think it advisable to mix two languages as
  this could develop into a bad habit.
- Anyone who knows enough about computers to be interested in this
  document may be assumed to be able to read english effordlessly,
  as virtually all literature on this subject is written in English.
- English has become the standard language in the computerworld.
  Having had first-hand experience with incompatabilities we see
  no reason why we shouldn't write this in English.


Note: Due to the limited processortime allocated to us this document
      was typed directly instead of being prepared on a wordprocessor.
      Typing mistakes may therefore occur.


A list explaining the difficult tecnical terms can be found in appendix
A.



                        Aim.

To build a multy-user multy-task operating system on a Z80. As no
fast disks are available everything is held in memory. The system
has been designed to be used with a slow external memory such as
a taperecorder or a floppy disk.

                        Underlying hardware.

JANOS is being developed for two computersystems, the Ordinator
computer at DJO Eindhoven and for the JEC 3.0 being built privately
by J. Bos. The main hardware features of both systems are:

- Z80 CPU (Normally at 4 MHz)
- Interrupt controlled I/O. There is no polling at all.
- A (programmable) timer interrupt.
- An MMU (Memory Mapping Unit) extending the amount of addressable
  memory to 512 Kb (Kilobytes=1024 (2^10) bytes).
The MMU works as follows:
The highest 4 addressbits of the Z80 are used to address a small but
very fast RAM. This RAM has 8 outputbits. One is used for writepro-
tection and the 7 other for addressing memory. The resulting address-
bus is 19 bits wide. The 12 lower addressbits of the Z80 form the
lower addressbits of the addressbus and the MMU the other 7.

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