Recovering Software from Forty-Year-Old Magnetic Tapes

In the early 1970s, Hewlett-Packard (HP) introduced the HP Interface Bus (HP-IB) as a standard way to interconnect the electronic instrumentation equipment they sold, automate its operation, and facilitate customers’ development of complex test and measurement systems. In 1975, the IEEE standardised HP-IB as the IEEE-488 bus, which was subsequently adopted by numerous manufacturers.

In 1976, HP shipped the 9825 desktop computer, which was optimised as a controller for HP-IB systems, and it became the centrepiece of many industrial test and measurement systems for years. After restoring four 9825 computers, Curious Marc and the crew turn to a collection of vintage 9825 software recorded on HP DC100 cartridge tapes in the 1970s and 1980s. Magnetic tape is one of the most reliable media for long-term data storage (modern LTO tapes claim 30 year data retention if properly stored, and assuming you can find a drive to read them that far into the future), but the DC100 mini-cartridges were not exemplary in that department, nor were the HP tape drives that used them. Thus begins another repair and recovery adventure which, when it finally pays off, allows demonstrating just how magical HP-IB was, and is: automatically testing an HP signal generator and spectrum analyser connected to one another and operated hands-off by the 9825 computer.

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