Dr Ian Logan was not a computer professional. The authors’ note in The ZX80 Companion (1980) introduced him as “a typical ZX80 enthusiast”: a member of his local hobby computer group, with “no professional connection with computing”, and a general medical practitioner. Over the next three years that enthusiast took apart the ROM programs of the ZX80, the ZX81 and the ZX Spectrum byte by byte, and published what each routine did. Then Sinclair Research asked him to help write one.
The computer press called him “Dr Logan”, and the title was a medical one. When Sinclair User visited him in 1983 he was running “a country practice in and around Lincoln” and living at Skellingthorpe, on the edge of the city. His two Spectrums were set up in a bedroom.
The ZX80 Monitor
The ZX80’s BASIC, screen and keyboard handling all lived in a 4K ROM, which Logan and his co-authors called “the monitor”. The ZX80 Companion, by Bob Maunder, Terry Trotter and Logan, was published by Linsac of Middlesbrough. Its second edition, printed in September 1980, has a chapter on the monitor. The copyright page notes that “Dr. Logan reserves copyright on Chapter 4”. The chapter maps the 4K: an operating system for the cassette, screen and keyboard, then the BASIC keyword table, the interpreter and the character set. It then shows readers how to examine the ROM for themselves with PEEK, and how to call its routines from their own programs. Reviewing that edition in November 1981, Your Computer said that with “Ian Logan’s full monitor listing” the book “really is the key to the fullest possible use of a 4K-ROM ZX-80”.
Melbourne House’s advertising went further, calling him the first person to disassemble the ZX80 monitor. No independent source confirms that he was first.
The ZX81 books and the Rosetta Stone
Logan’s next books were published by Melbourne House, and together they covered the ZX81’s 8K ROM:
- Understanding Your ZX81 ROM was advertised as new in November 1981. It explained Z80 machine code through examples from the ROM, described how the ROM was organised, and included a section on using machine code routines from BASIC. It cost £8.95.
- ZX81 ROM Disassembly Part A (£7.00) listed every location from
0000Hto0F54H, covering “all the operating functions of the ROM except the floating point calculator”. - ZX81 ROM Disassembly Part B (£8.00) covered
0F55Hto1DFFH: the routines that evaluate an expression and the floating-point calculator. It was written with Dr Frank O’Hara, who would co-author his Spectrum disassembly too.
Both parts were on sale by June 1982.
The ZX81 work also won Logan an American prize. In March 1982 SYNTAX ZX80, a newsletter for Sinclair users published by the Harvard Group in Massachusetts, reported that “Dr. Ian Logan of Skellingthorpe, UK, a frequent SYNTAX contributor” had won its first annual Rosetta Stone award, sponsored by Mindware Co. The award was for “the best independent product” for the ZX80 or ZX81, whether an application, a software package or a peripheral, and Logan won $100, a magazine subscription and a Rosetta Stone replica “for his 8K ROM disassembly”. Melbourne House put a photograph of him receiving it in its advertisements that summer, under the headline “Why is this man smiling?”
The Spectrum
The same advertisement, in September 1982, announced that Logan was working on Understanding Your Spectrum. The book is dated “Lincoln, England 1982” and sold for £7.95. Sinclair User reviewed it in May 1983 and said Logan taught the Spectrum’s BASIC, its Z80 machine code and its ROM “in a very expert manner which even the beginner should understand”.
The Complete Spectrum ROM Disassembly, with Frank O’Hara, followed in 1983 at £9.95. The authors signed the preface in January 1983, Logan from Lincoln and O’Hara from London. The book works through the whole 16K ROM in ten sections, from the restart routines and the keyboard scan to the floating-point calculator. It explains what each routine does and how the routines call each other. In the preface they wrote that “between us we have unravelled the ‘secrets of the Spectrum’”.
Three years later CRASH was still sending readers to the pair. Asked where to find a disassembled ROM listing in August 1986, its technical column answered that Logan’s two Spectrum books were “by far the best I’ve seen”. It suggested starting with Understanding Your Spectrum and moving on to the disassembly for more detail, warning that “the book is not easy reading”.
Working for Sinclair
In December 1982 Logan went to Sinclair Research in Cambridge, and, as he told Sinclair User, “Nigel Searle asked me if I would like to do some work and I could write a book about it.” The work was the software for the ZX Microdrive, Sinclair’s tape-cartridge storage drive, and the ZX Interface 1 that connected it to the Spectrum. The Spectrum’s own 16K ROM knows almost nothing about these devices, so the Interface 1 adds a second, 8K “shadow” ROM that pages in over the first. As Logan’s book explains it, the trick is that statements which used to stop with an error report are now carried out: type CAT 1 on a bare Spectrum and it fails; with the Interface 1 and a Microdrive attached, the shadow ROM catches it and lists the cartridge.
He did the work at a distance. The program was developed on EPROM chips, and when there were corrections Logan would “go to Cambridge with the alterations and we would blow a new EPROM”. In February 1983, with the Microdrive delayed again, Clive Sinclair declined to address a meeting of the Institution of Electrical Engineers because no working model was ready to show. Logan was one of the last-minute speakers instead. He gave nothing away, Sinclair User reported, except this: “I may have written the software for the device but to be honest I don’t know what is on the other end of the wire.”
Logan himself described his part modestly. In the preface to his Spectrum Microdrive Book (1983) he wrote that he had “had the pleasure of assisting in the writing of the ‘shadow’ ROM software”, and that “the ‘lion’s share’ of the work has been done by Martin Brennan and Ben Cheese of Sinclair Research Ltd.” Sinclair User’s November 1983 interview drew the line in the same place. Logan wrote the Microdrive part of the ROM, and Brennan designed the network and wrote most of its software. The same interview reported that at least 1,000 Microdrives had reached customers with the program still on EPROM, and that Logan knew of “two definite bugs” he hoped would be fixed before it went into ROM.
The job put limits on what he could publish. Sinclair asked that details “that might compromise the ‘security’ of the Microdrive” be left out of his book, and his Microdrive chapter opens with a note saying so. CRASH still called it “the best technical book on the Microdrive” in November 1985, while complaining that it was “boringly titled”. It added that Logan “actually wrote a part of the shadow ROM”, and that “his contract with Sinclair prevented him from giving away a few details of the system”.
The Jupiter Ace
In December 1982 the first newsletter of the Jupiter Ace users’ club carried a postscript about Logan. He had “apparently obtained a listing of the Rom by cross-loading from the Jupiter to the Spectrum. The cassette standards are apparently identical.” The editor, John Noyce, repeated the claim second-hand, and no other public source confirms it. It hints at how Logan might have got into the Jupiter Ace, which Steven Vickers and Richard Altwasser had designed after leaving Sinclair.
Sources
- Bob Maunder, Terry Trotter and Ian Logan, The ZX80 Companion, 2nd edition (Linsac, Middlesbrough, September 1980): copyright page (“Dr. Logan reserves copyright on Chapter 4”); authors’ note (general medical practitioner, “typical ZX80 enthusiast”); chapter 4, “The ZX80 Monitor”, section 4.1, p. 51.
- Your Computer, November 1981: book review of The ZX80 Companion, second edition (“Ian Logan’s full monitor listing”); Melbourne House advertisement announcing Understanding Your ZX81 ROM and calling Logan the first person to disassemble the ZX80 monitor. The same advertisement appears in Computer & Video Games issue 1, November 1981, p. 40.
- Your Computer, July 1982: Melbourne House advertisement describing Understanding Your ZX81 ROM (164 pages) and the two ZX81 disassemblies.
- Sinclair User issue 3, June 1982, p. 8: Melbourne House advertisement for ZX81 ROM Disassembly Parts A and B, with their address ranges and contents.
- SYNTAX ZX80 vol. 3 no. 3 (The Harvard Group, March 1982), p. 1: “Ian Logan wins first annual Rosetta Stone”.
- Sinclair User issue 5, August 1982, and issue 6, September 1982, p. 4: Melbourne House advertisement (“Why is this man smiling?”), with prices of £8.95, £7.00 and £8.00 and the announcement of Understanding Your Spectrum.
- Ian Logan, Understanding Your Spectrum (Melbourne House, 1982): title page and copyright. Price £7.95 from Your Computer, July 1983, Melbourne House advertisement.
- Sinclair User issue 14, May 1983, p. 89: review of Understanding Your Spectrum.
- Ian Logan and Frank O’Hara, The Complete Spectrum ROM Disassembly (Melbourne House, 1983): preface dated January 1983; contents and introduction. Price £9.95 from Sinclair User issue 12, March 1983, p. 8, Melbourne House advertisement.
- CRASH issue 31, August 1986, p. 101: Tech Tips on Logan’s two Spectrum books.
- Sinclair User issue 13, April 1983, p. 16: news report, “Microdrive delay”, on the February meeting of the Institution of Electrical Engineers and Logan’s remark there.
- John Gilbert, “Microdrives are still being developed”, Sinclair User issue 20, November 1983, pp. 65–66: interview with Logan at home near Lincoln; starting work for Sinclair in December 1982; EPROM development; Brennan’s role; the remaining bugs.
- Ian Logan, Spectrum Microdrive Book (Melbourne House, 1983): preface (the shadow ROM, Martin Brennan and Ben Cheese); chapter 1, “The Extended Spectrum System” (the 8K shadow ROM and the
CAT 1example); chapter 3, “The Microdrive”, author’s note, p. 21. - CRASH issue 22, November 1985, p. 118: Tech Tips, “A book at bugtime”.
- Ace User issue 1, December 1982, p. 4, the Jupiter Ace Users Club newsletter, ed. John Noyce: postscript on Logan and the Ace ROM.