Prerequisites and installation

UniDOS is designed to be installed in a ROM board expansion (we would recommend the FlashGordon from PulkoTronics).

Please, refer to your Rombard user manual to learn how to install ROMs.

You will need to install UniDOS ROM itself and DOS nodes ROMs which fit your requirements and the peripherals you wish to use. You will need at lead two free ROM slots.

Caution: current UniDOS version works only with CPC equipped with firmware version 3 or 41).

In case of installation problem, UniDOS will automatically disable itself so that your system will remain usable. UniDOS can also be manually disabled by pressing ESC during the boot sequence.

UniDOS installation

The latest version of UniDOS can be found in the download section.

UniDOS shall always be installed in a ROM slot lower than AMSDOS. It means that if AMSDOS is at its original slot 7, UniDOS shall be installed in slots 1 to 6.

Minimal configuration: (no replacement of internal ROM 7)

  • ROM 1, 2, 3, 4, 5 or 6: UniDOS
  • ROM 7: AMSDOS (internal ROM 7)
  • ROM …: DOS nodes (see DOS nodes installation bellow)

But for an optimal compatibility, it is advised to move AMSDOS to ROM slot 15 and to install UniDOS in ROM slot 7 (the original AMSDOS slot). That way, numerous programs which are resetting ROM 7 at start will work under UniDOS without any drawback. Unfortunately, this configuration is not possible on CPC6128 without patching the motherboard to disable the internal ROM 7.

Optimal configuration: (replacement of the internal ROM 7)

If you cannot replace the ROM 7 but own a Rombard which is capable to replace the firmware you can use an alternate optimal configuration by configuring the patched firmware “u5” from the download page.

Alternate optimal configuration: (with the patched firmware “u5”, without remplacement of internal ROM 7)

  • ROM 5: UniDOS
  • ROM 6: ParaDOS (optional)
  • ROM 7: AMSDOS (internal ROM 7)
  • ROM …: DOS nodes (see DOS nodes installation bellow)

In anycase, UniDOS works together with the original AMSDOS ROM to manage the floppy disc drives. UniDOS is also compatible with the famous ParaDOS ROM from Richard Wilson which you can use instead of AMSDOS.


  • On CPC6128, it is required to patch the motherboard to disable the internal ROM 7 so that you can reconfigure it through an external Rombard (other CPC models to not have this issue).
  • To install the patched firmware “u5”, you need a Rombard which is capable to reconfigure the firmware such as the X-Mem.
  • ParaDOS is normally not able to work in ROM slot 15, but you will find a patched version in the download section which fixes this issue.
  • If AMSDOS/ParaDOS are not installed, UniDOS will not handle the floppy disc drives but all other features and additional drives will operate normally.
  • If you use the Utopia ROM from Arnord Ltd., always install it in a slot greater than UniDOS and lower than AMSDOS/ParaDOS3).

Once UniDOS is installed, at boot you may read the message:

 Warning: UniDOS found no NVRAM!        
          Activating degraded mode      
          Please, finalize install      

This warning is normal because UniDOS needs at least one DOS node with non volatile memory support to operate. You can continue with the installation of DOS nodes as described in the section bellow.

DOS nodes installation

You will find the list of the available DOS nodes in the download section.

Caution: do never install a DOS node with a version number greater than the one of UniDOS ROM.

DOS nodes are ROMs which are specific to UniDOS to add management of new drives. These drives can be related to an interface (board with USB ports, microSD card readers…) or be pure virtual drives (like the “Zero” DOS node).

DOS nodes can be either extension ROMs (type 2) or background ROMs (type 1). In this second case, in addition to add a DOS node to UniDOS, they can also provide new RSX to the system.

Some DOS nodes, can additionally provide non volatile memory support. UniDOS use this feature to retain the user's current context (more details are given in the user manual).

DOS nodes can be installed in any ROM slot bellow number 32. Nevertheless, if a DOS node also features RSX (i.e. is a background ROM) it will have to be installed in a slot bellow 16 so that the operating system can initialize it.

At least one DOS node with non volatile memory shall be installed so that UniDOS can operate. If several DOS nodes are providing the non volatile memory feature, only the one provided by the DOS node in the lowest slot will be used.

Example of a complete configuration:

  • ROM 5: Albireo (DOS node with non volatile memory support)
  • ROM 6: Zero (another DOS node)
  • ROM 7: UniDOS (UniDOS ROM itself)
  • ROM 15: AMSDOS/ParaDOS4)

Once your DOS nodes are installed, you should see the following message at boot:

 UniDOS (integrated) ©2021 Futurs'

During DOS nodes initialization phase, you will see dots being displayed, one per detected DOS node.

Note: you will read the notice standalone instead of integrated if AMSDOS/ParaDOS is not installed.

Here is an example of what you could see once all your ROMs are installed5):

ROM  1:NOVA             0.10!extension
ROM  7:UNIDOS           1.32 back &A700
ROM  8:FATFS            1.21 background
ROM 27:ALBIREO          1.20 extension
ROM 28:ZERO             1.10 extension

Albireo DOS node

This DOS node is standard and has no installation specificity. Just put it in any slot lower than 32.

M4 DOS node

This DOS node is standard, but since it is a background ROM, it has to be installed in a ROM slot lower than 16 so that its additional RSX are visible to the system.

Moreover, you will also have to take care of the M4 Board configuration; in order to avoid conflicts, the M4 Board built-in ROM must be moved to a slot greater than 16 so that it is no longer initialized by the system (but it will still be used internally by UniDOS).

For instance, slot 127 is a good value:

FatFs DOS node

This node requires more attention than the others during its installation.

Actually, it is composed of three different ROMs which have to be installed as followed:

  • FATFS-P1.ROM : main ROM which provides FatFs support.
    → Must be installed in any slot which is both lower than 16 and greater than the one of UniDOS.
  • FATFS-P2.ROM : low level ROM which provides IDE support (X-Mass, Symbiface II or compatible).
    → Must be installed in any slot lower than 128.
  • FATFS-FT.ROM : FatFs format ROM which provides routines to initialize FAT filesystem; please note it is optional and that it can be omitted once your disk is formatted.
    → Must be installed in any slot lower than 128.

Once installed, because of FAT management, this DOS nodes allocates a significant amount of memory. If it should not be an issue with modern softwares which are properly using the operating system, it could prevent some games and old softwares to start (because they will trash the memory without checking what is already allocated). It is possible to avoid this issue with the help of the Nova from PulkoTronics. When this card is detected, the FatFs DOS node automatically takes advantage of it and donot use main memory anymore (please note that the FatFs DOS node will also disable its non volatile memory management to ensure that the one provided by the Nova DOS node is always used, even if installed in a slot greater than FatFs).

Nova DOS node

This node is standard and has no installation specificity, but it is advised to install it bellow any other DOS node so that its non volatile memory management is always used first.

Zero DOS node

This node is standard and has no installation specificity. Just put it in any slot lower than 32.

the one of the CPC6128 or 464plus and 6128plus
Only ParaDOS patched version can work in slot 15, see bellow
for instance: UniDOS in slot 7, Utopia in slot 8 and AMSDOS/ParaDOS in slot 15
patched version of ParaDOS to be able to work in slot 15 only
through the |NODE RSX.