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