Sustainability of Digital Formats: Planning for Library of Congress Collections

The HFE (HxC Floppy Emulator) File Format is designed for use with the SD HxC Floppy Emulator hardware, which is based on the PIC18F family of microcontrollers. This format serves as an optimized floppy image format, encompassing both the floppy disk image and crucial metadata. The metadata, stored in the file's header (the initial 512 bytes), includes information such as the number of tracks, the valid "side" of the disk, track encoding method, bitrate, rotations per minute, floppy interface mode, floppy write protection mode, and other encoding flags.

The HFE file format comprises three essential components: the header, the track offset Look-Up Table (LUT), and the track data. The file header spans 512 bytes, the track offset LUT can be up to 1024 bytes, and the track data has an open size. The header encapsulates vital details about the file, defining its structure and encoding.

As stated in the specification, a track data is essentially a table containing the bitstream of a track from the floppy disk. This track data can employ various encoding methods, including Modified Frequency Modulation (MFM), Frequency Modulation (FM), Group Coded Recording (GCR), or custom encoding. Each track is divided into blocks of 512 bytes, with each block containing a portion of both Side 0 and Side 1 tracks, and these blocks alternate in the track data.

Documentation about the format structure and its variants is available on HFE HxC Floppy Emulator file format specifications with a high level description of changes between the versions. Comments welcome.

SDCard HxC Floppy Emulator HFE File format, Rev.1.1. 06/20/2012 and HFE HxC Floppy Emulator file format, Rev.3.1 - 05/22/2019 (which also covers the high level changes between earlier versions). See more details at HFE HxC Floppy Emulator file format specifications. Source code for multiple versions are available on Jean-François Del Nero's HxCFloppyEmulator GitHub repo. Comments welcome.

HxC software boasts "tens of thousands" of installations according to its official website. While specific statistics on the file format are not provided, it is known that this file format is utilized by various applications beyond the HxC Floppy Emulator Project.

Notably, the file format is employed by GoTek, a floppy emulator hardware, as well as FlashFloppy, which serves as floppy emulator software specifically designed for GoTek. Additionally, it finds application in Clock Signal (CLK), an emulator catering to 8-bit and 16-bit computers; beebjit, an emulator tailored for the BBC 8-bit microcomputer; and B-em, as indicated by a pull request highlighting the addition of HFE support. This establishes the widespread and diverse usage of the file format across different emulation platforms and hardware.

Comments welcome.

The HFE file format comprises three essential components: the header, the track offset Look-Up Table (LUT), and the track data. The file header spans 512 bytes, the track offset LUT can be up to 1024 bytes, and the track data has an open size. The header encapsulates vital details about the file, defining its structure and encoding.

As stated in the specification, a track data is essentially a table containing the bitstream of a track from the floppy disk. This track data can employ various encoding methods, including Modified Frequency Modulation (MFM), Frequency Modulation (FM), Group Coded Recording (GCR), or custom encoding. Each track is divided into blocks of 512 bytes, with each block containing a portion of both Side 0 and Side 1 tracks, and these blocks alternate in the track data.

HFE self-identifies with Magic Numbers.

HFE was developed by Jean-Francois Del Nero in 2006 to load legacy video games from Atari ST and Amiga machines, which required floppy disks. The project grew organically from user requests and now supports “hundreds of machines and floppy formats”.

Del-Nero’s purpose in HFE’s development was to “completely replace the floppy disk drive by an electronic device”. The hardware is available as an SD Card, a USB drive, and what it describes as "advanced firmware."

The official website also includes firmware schematics and emulator software.

HFE has several versions:

• 29 November 2010 - v1.0 : Initial version.
• 20 June 2012 - v1.1 : Add single_step, track0s0/1_altencoding and track0s0/1_encoding header fields.
• 8 July 2012 - v2.0 : Add opcodes support in stream (HFEv2).
• 4 August 2017 - v3.0 : Opcodes redefinition/redesign.
• 22 May 2019 - v3.1 : Add weakbits support on HFEv3.