SIDE3 Loader

After my completely rewritten firmware for Ultimate 1MB, Incognito and SIDE/SIDE2 transformed the usability and functionality of those devices and brought tremendous added value to the end user, I am proud to present the SIDE3 Loader for the exciting new SIDE3 cartridge. This fantastic device – designed by Candle O’Sin and sold by Lotharek and RetroLemon – has all the functionality of SIDE2, plus cartridge emulation and many other powerful improvements. Features include:

  • Use of inexpensive, easily sourced SD cards instead of CF cards
  • Emulation of a wide range of cartridge types, up to 1MB in size
  • Real time clock with battery-backed NVRAM
  • A massive 8MB of flash ROM and 2MB of fast SRAM
  • Versatile ROM/RAM access with DMA engine
  • Hot-swappable media
  • Dual mode (SDX/Loader) operation, controlled by switch
  • Menu button (doubles as ATR swap button when used with U1MB)
  • Excellent build quality with stylish case design

The SIDE3 loader likewise represents a step forward from the previous SIDE/SIDE2 loader. Features include:

  • Up to 1,024 FAT filenames in memory (no more paging through long folders)
  • Mount cartridges, ATRs and partitions simultaneously, all from the same menu
  • Special RAM-based operating system permits booting of some ATRs without U1MB
  • Tight integration with U1MB where present (using special SIDE3 U1MB plugins)
  • Powerful recursive search facility which runs in the background while you browse results
  • Handling of up to fourteen FAT partitions
  • APT browser allows dynamic mounting of hard disk partitions
  • Easy mounting of multi-disk volumes via MAP files
  • Built-in mini DOS allows read-only access to FAT16/FAT32 volumes on ‘D1:’
  • Built-in ‘Pulse Density Modulation’ (FujiConvert) audio file playback
  • Built-in Covox support
  • Built-in real time clock support


You can download the latest (development) versions of the SIDE3 loader via the links below.

SIDE3 Loader 0.44 (July 2021)

Fixes in build 0.44:

  • SDXC media description in Device menu

See the changelog for full details.

For proper Ultimate 1MB operation with SIDE3, please visit the U1MB Firmware page and download and install the U1MB Firmware with SIDE3 PBI BIOS and plugin.

SpartaDOS X 4.49e for SIDE3 is available here.

Note: the SIDE3 U1MB main BIOS plugin and PBI BIOS are not compatible with the SIDE and SIDE2 cartridges. You will need to re-install the SIDE/SIDE2 plugin and PBI BIOS to regain full functionality with the older cartridges.


The loader archive contains a self-contained XEX which you can copy to you SD card and launch directly from the loader currently installed on your cartridge. See the README for further details.

Loader Quick Reference


See the XEX Loader section in the U1MB/Incognito/SIDE firmware manual for details of how to use the new loader.

Licensing and Donations

While the firmware is free at the point of delivery for personal use, if it is to be included on commercially sold devices, the firmware is subject to a licensing fee which should be arranged with the author in advance. Developers interested in customised versions of the firmware tailored to their particular hardware should contact the author.

In light of the fact that firmware licensing revenue is modest and that updates are offered for free to the end user, donations are welcomed and appreciated. Indeed, it has been my mission to facilitate easy and safe firmware updates, and regular in-the-field upgrades are encouraged to ensure that devices remain up to date and bug fixes are delivered in a timely manner.

Thank you!

SIDE3 Videos