Ultimate 1MB 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 Ultimate 1MB. 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 Ultimate 1MB 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 CPU type, audio and video hardware, and more
  • User-selectable BIOS hotkeys
  • Dual configuration profiles
  • BIOS plugin API for user-defined external device control
  • New, faster XEX loader supporting multiple FAT partitions, APT partition mounting and rapid, recursive searching
  • Dedicated High-Speed SIO menu
  • SIO2BT support (at up to 56kb/s) and high-speed SIO for PCLink and other serial devices
  • Built-in CIO “Z:” RTC device handler
  • Rapidus plug-in and support for PBI BIOS extensions in fast linear 65C816 RAM

New Firmware Download

Three separate files comprise the main BIOS, PBI BIOS and SIDE Loader, and all components should be updated at the same time. Alternatively, one may update the entire 64KB firmware block using the latest version of UFLASH. For installation instructions, please refer to the user manual.

Ultimate1MB Firmware Update 07 Dec 2016 (ZIP)

Note: Owners of Ultimate 1MB with the original v.1 CPLD code from Candle’s first run of boards must ensure that they update to the current JED prior to installing the new BIOS. Boards with the PBI feature (including all manufactured by Lotharek and those from Candle’s second run) will safely run the new BIOS without modification.

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, configuration data layout and Plugin architecture 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.

SpartaDOS X 4.47 ROMs for Ultimate 1MB

To complement the new Ultimate 1MB BIOS, two sizes of SpartaDOS X ROM are provided (192KB and 256KB). The smaller (192KB) image allows flashing of the WIP Graphical OS alongside it. Both 192KB and 256KB SDX ROMs include the FDISK APT partitioning tool and other hard disk utilities on the CAR: device.

192KB and 256KB SDX 4.47 for Ultimate 1MB

Use Tools->Set SDX Size in UFLASH to switch between available SDX ROM sizes prior to flashing. The 192KB setting enables the GOS in BIOS setup.

Original PBI BIOS and SIDE Loader

The APT BIOS for Ultimate 1MB provides an OS-compliant PBI hard disk and high-speed ATR disk image mounting when SIDE Hardware is enabled in BIOS Setup. Note: PBI BIOS v.1.0 should be used only with Candle’s original Ultimate 1MB main BIOS.

Ultimate PBI BIOS v.1.0 (ZIP)

There are two ways to update the PBI BIOS in your Ultimate 1MB. You can either use the 8KB ROM image for use with uflash, or the stand-alone upgrade utility. Both are included in the ZIP.

You may also download Candle’s original SIDE Loader for Ultimate 1MB using the link below:

Ultimate SIDE Loader (ZIP)


The APT Toolkit user guide may be downloaded from the APT documentation page. The BIOS documentation may be downloaded via the link below:

PBI BIOS v.1.0 for Ultimate and Incognito


While it has been my privilege to write software for Ultimate 1MB, Incognito and SIDE, I enjoy no licensing agreements with hardware vendors. Since the hardware itself cannot function without firmware, please consider making a small donation (via the “Donate” button) to help ensure the continuation of software development and technical support. Donations also assist with website hosting and equipment costs.

Thank you!