Despite such overlap between their histories, Voyager didn’t use a microprocessor \u2014 the first such marriage was between Intel’s 4004 and Pioneer Venus<\/a> in 1978. Yet Voyager 1’s computer issue in 2023<\/a> and the subsequent epic eight month fault finding and interstellar firmware update, as space vlogger Scott Manley so aptly called it<\/a>, revealed some intriguing parallels between the 48-year old spacecraft and the Sinclair ZX Spectrum, in particular the Spectrum 128, launched in 1986, the same year Voyager 2 was speeding over Uranus’ clouds.<\/p>\n The Voyager design has three computers<\/a>, each doubled up for redundancy and peak processing. The ones handling navigation, communication and instrument control, are duplicates or derivatives of systems previously used on the Viking Mars missions, so were relatively well documented. The third, the Flight Data Subsystem or FDS, was designed as entirely novel to Voyager. It had to be as fast and flexible as possible to cope with the flood of planetary encounter data, so had to use the most advanced tech of the time that incurred acceptable risk.<\/p>\n Thus, the FDS uses solid state dynamic memory, DRAM, instead of the magnetic storage of the other systems. This is 8k of 16-bit words, the same total storage of the original 16k 8-bit bytes of DRAM in the original entry-level Spectrum. The Spectrum used eight memory chips to the Voyager’s 512 and was more compatible with a household budget. Got to love Gordon Moore<\/a>.<\/p>\n Also like the Spectrum, the Voyagers have no modern operating system, the built-in software is hand-crafted machine code written in assembler and performing specific tasks. By the time the problem occurred, the small Voyager team had very spotty documentation leading to a lot of reverse engineering. By the time the ZX Spectrum 128 was in development, the original source code was also poorly documented and written for a lost assembler program, needing considerable reverse engineering to be rebuilt \u2014 your correspondent\u2019s first job as a coder. Degree of difficulty very different, resonance nonetheless.<\/p>\n Although it addressed 8K words of memory, the FDS’s architecture could only manage twelve bits of address space, enough for 4k. The memory was therefore divided into two 4K pages, with the processor switching between them. That this complicated software design required paging out while running code<\/a> because it needs to access the other page, is fraught with danger. The 280 in the Spectrum 128 can only access 64k of memory, so uses the same trick to access all of its titular 128K. Rather thrillingly, the assembler instruction to do the switch, OUT, is the same on both platforms, being more commonly used to OUTput control signals to hardware such as the paging logic. As the z80’s instruction set was based on that of 1974’s 8080 developed at the same time as the FDS, convergent evolution is no surprise.<\/p>\n![\"Voyager](\"https:\/\/www.newsbeep.com\/ie\/wp-content\/uploads\/2025\/09\/1757962751_170_nasa_voyager_probe.jpg\")
\nAfter nearly half a century in deep space, every ping from Voyager 1 is a bonus
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\nThe Reg chats with Voyager Imaging Team member Dr Garry E Hunt
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