Incognito BIOS and SIDE Loader

In 2012, Sebastian Bartkowicz (Candle) asked me if I could write a BIOS to realize the PBI hard disk functionality he was developing for the Incognito. During the months that followed, Candle thought of more and more things to add (such as the ability to read and write disk images mounted in the FAT partition of the CF card), and after weeks of coding and debugging, we had something approaching a final version.

In 2015, a desire to significantly broaden the functionality of Incognito and correct some problems with the PBI BIOS led me to completely re-write the the firmware for the device, including the main BIOS, PBI BIOS and XEX loader. Among new features provided by the firmware are the following:

  • A PBI implementation of Matthias Reichl’s High-Speed SIO code which does not require OS patching and which works with external cartridges
  • The ability to set the system date and time from inside the BIOS setup utility
  • Expanded PBI BIOS settings on a dedicated menu page
  • System information page showing video standard, CPU speed, etc
  • User-selectable BIOS hotkeys
  • Configuration profiles
  • BIOS plugin API for user-defined external device control
  • New, faster XEX loader supporting multiple FAT partitions, APT partition mounting and recursive searching
  • SIO2BT support (at up to 56kb/s) and high-speed SIO for PCLink and other serial devices
  • Built-in CIO “Z:” RTC device handler

New to Version 2

Version 2 of the alt firmware brings several improvements, including:

  • Number of configuration profiles increased from two to three
  • Greatly increased XEX loading speed
  • Numerous usability improvements to the loader and BIOS setup menu
  • Better control of internal BASIC state
  • Improved compatibility with SD/CF adapters
  • Several critical bug fixes


Incognito Firmware Update (July 2018)

The firmware consists of three separate files: the Main BIOS, PBI BIOS and SIDE loader. All three should be updated at the same time, and the machine power-cycled. As well the the ROMs, the archive contains UFLASH. Installation instructions may be found in the user manual.

User Manual

The User Manual contains installation instructions and usage notes for the Main BIOS setup utility and SIDE/XEX Loader:

Ultimate 1MB, Incognito and 1088XEL-U1MB Firmware Manual

Technical Documentation

Technical documentation describing the firmware memory map and configuration data layout is provided below:

Ultimate 1MB, Incognito and 1088XEL-U1MB BIOS Technical Documentation


If wish to report any issues with the new firmware of have any suggestions on how it might be improved, you may email me directly via the address on the contact page, or post in the discussion thread on the AtariAge Forum.


While it has been my privilege to write software for Ultimate 1MB, Incognito and SIDE, I enjoy no licensing agreements with hardware vendors. Nevertheless, since the PBI BIOSes and APT tools are integral to the functionality of these devices, please consider making a small donation (via the “Donate” button) to help ensure the continuation of software development and technical support. Donations also help with website hosting and equipment costs.

Thank you!