Recovery of heritage software stored on magnetic tape for Commodore microcomputers

Abstract

Digital games make up a significant but little known chapter in the history of the moving image in Australia and New Zealand.  Beginning in the early 1980s, the Australasian software industry developed a remarkable record of content creation. The ``Play It Again'' project is conducting research into the largely unknown histories of 1980s game development in Australia and New Zealand, ensuring that local titles make it into national collections and are documented and preserved, enabling the public to once again play these games.

Microcomputers from the 1980s made extensive use of compact audio cassettes to distribute software as an inexpensive alternative to the floppy disk technology available at the time. Media from this era are at risk of degradation and are rapidly approaching the end of their lifespan. As hardware platforms and peripheral devices become obsolete, access to the data for future scholars and other interested parties becomes more difficult. In this article, we present a case study, wherein we investigate the issues involved in making digital copies with a view to the long term preservation of these software artefacts.

A video game title stored on standard compact cassette for Commodore's popular VIC-20 machine, ``Dinky Kong'' by Mark Sibley was recorded using both inexpensive amateur and professional playback equipment. The audio files obtained were processed using freely available software, alongside a customised decoder written in MATLAB and Perl. The resulting image files were found to be playable using an emulator. More importantly, the integrity of the data itself was verified, by making use of error detection features inbuilt to the Commodore tape format, which is described in detail.

Issues influencing the quality of the recovered image files such as the bit rate of the digital recording are discussed. The phenomenon of audio dropout on magnetic tape is shown be of some concern, however there exist signal processing techniques to compensate for such errors.

The end result of the imaging process was a file compatible with a popular Commodore VIC-20 emulator, the integrity of which was verified by using inbuilt checksums.