Digital Archeology: Recovering Digital Objects from Audio Waveforms

Specimens of early computer systems stop working every day. It is necessary to prepare ourselves for the upcoming situation of having storage media and no working systems to read data from these carriers. With storage media residing in archives for already obsolete systems it is necessary to extract the data from these media before it can be migrated for long term preservation. One storage medium that was popular for home computers in the 1980s was the audio tape. The first home computer systems allowed the use of standard cassette players to record and replay data. Audio tapes are more durable than old home computers when properly stored. Devices playing this medium (i.e. tape recorders) can be found in working condition or can be repaired as they are made out of standard components. By re-engineering the format of the waveform the data on such media can then be extracted from a digitized audio stream. This work presents a case study of extracting data created on an early home computer system, the Philips G7400. The original data formats were re-engineered and an application was written to support the migration of data stored on tapes without using the original system. This eliminates the necessity of keeping an obsolete system alive for preserving access to data on storage media meant for this system. Two different methods to interpret the data and eliminate possible errors in the tape were implemented and evaluated on original tapes recorded 20 years ago. Results show that with some error correction methods parts of the tapes are still readable, even without the original system. It also becomes clear, that it is easier to build solutions now when the original systems are still available.