The Dragon 64 was a Dragon 32 with twice the memory, a serial port and keys that repeated when held down. It went on sale in the United States before Britain, through a New Orleans company called Tano, and reached British shops at the end of 1983 at about £225. Its most interesting feature was invisible: switched on, it was a Dragon 32, and it had to copy a second BASIC into its own RAM before it could become a 64.
Your Computer was not impressed. The extras, its reviewer wrote, “are loosely cobbled on to the 32 rather than being an integral part of the machine”. The reason to buy one was an operating system the Dragon 32 could not run: Microware’s OS-9.
Fast facts
- Released: 1983, in the US through Tano; in Britain from late 1983.
- Price: £229 in the shops in January 1984; £225 in advertisements that spring.
- CPU: Motorola 6809E at 0.89 MHz, as in the Dragon 32.
- RAM: 64K.
- ROM: the Dragon 32’s BASIC, plus a second BASIC that the 64K mode runs from RAM.
- Additions: RS-232 serial port on a 7-pin DIN socket, keyboard auto-repeat.
- Graphics and sound: as the Dragon 32.
Transatlantic first
In 1983 Dragon Data tried to sell the Dragon in America, home of the machine it was based on, Tandy’s Color Computer. It formed a joint company with Tano Corporation of New Orleans, which built and distributed the Dragon 64 there. Dragon User reported that the American machine was “exactly the same as the UK’s version with the exception of the power supply and the video output”, and that Tano expected to sell 250,000 in the first year. By spring 1984, according to a later history of the Color Computer, Tano had cut the price to $149 to clear its stock.
The British Dragon 64 made its first public appearance at a show that autumn. When Dragon User tested it in December 1983, the same machine had been on sale in the US “for the past couple of months”.
The 64K is a bootstrap, not a switch
The extra 32K does not sit beside the ROM; it sits on top of it. The SAM chip’s map type 1 gives a flat 64K of RAM from 0000 to FEFF, and in doing so “the extra 32K of RAM therefore overlays the BASIC ROM and expansion addresses which means that neither the Extended Color BASIC ROM nor the cartridge ROM can be accessed”.
So the machine cannot simply turn its memory on. It starts as a Dragon 32. Typing EXEC runs a bootstrap that copies a second BASIC into the RAM that is about to cover the ROM, reading a byte in map type 0, switching to map type 1, writing it, and switching back for the next. Only once BASIC is running from RAM at C000–FEFF does the machine become a 64. Your Computer’s reviewer found 16,370 more bytes free for BASIC than on the 32.
Two consequences follow, and the user sees both.
The cursor changes colour. “The 64K mode can be distinguished from the 32K mode by the fact that the cursor flashes blue rather than black.” Nothing else on the screen changes, so the cursor is how you know which machine you are using. Your Computer noticed the same thing: “you are greeted by exactly the same turn-on screen but this time the cursor has turned blue”.
And there is no way back. “Once in 64K mode, there is no easy way to return to the 32K mode since a reverse bootstrap has not been provided.” Smeed and Sommerville give three POKEs that look as though they should put the machine back, then explain that they do not: reverting “requires resetting the interrupt vectors and changing various other addresses and pointers”.
BASIC in RAM, and the checksum that guards it
With the interpreter in RAM, a program can change it, which is useful and dangerous. Dragon Data’s answer is a 16-bit checksum. FLAG64 at $11A records whether a restart is warm or cold, and $11B–$11C hold a total taken while BASIC was copied. On reset the total is recalculated, and a mismatch forces a cold boot that copies BASIC in again.
The book explains why: it “avoids the problem of users or programs poking the BASIC in RAM thus causing the system to crash and then performing a warmboot which would not restore the correct BASIC system”. Then it shows how to get round the check. RECSUM adds up the bytes from $C000 to $FF00 and stores the result in CSUM64, so a modified BASIC passes the check and survives a reset.
The serial port
The RS-232 interface uses a 7-pin DIN socket, is standard on the 64 and works in both modes. It adds DLOAD and DLOADM, the equivalents of the cassette commands for loading programs from another computer, backed by three routines in the I/O jump table: SERIN at $802A, SEROUT at $802D and SERSET at $8030. SERSET offers seven speeds from 110 to 9600 baud, and the port starts at 1200.
One byte redirects printing: PRNSEL at $3FF, zero for the Centronics port and non-zero for the serial one.
OS-9
OS-9 was a multitasking operating system for the 6809, written by the American company Microware. Your Computer explained that it “needs the memory space available to the 64 and cannot operate on the 32”. It also needed a disk drive. Dragon Data’s version was expected in the shops in February 1984, at about £40 for the operating system itself, with business programs and languages to follow. Dragon User’s reviewer that April said that if Sir Clive Sinclair had not already taken the phrase for his QL, he would be tempted to call it a “quantum leap” for the Dragon. OS-9 loads programs as modules that can run wherever they land in memory, the kind of position-independent code the 6809 was designed for.
“Loosely cobbled on”
Your Computer’s David Scobie reviewed the machine in January 1984 and was unpersuaded. The 64 “is really a Dragon 32 with extra memory, an RS-232 port and auto repeat on the keyboard. These are loosely cobbled on to the 32 rather than being an integral part of the machine.” His specific complaint follows from the bootstrap: “Execs and Peeks and Pokes are needed to use most of the new facilities when they should be an integral part of the machine.”
The technical documentation bears him out. Every extra that Inside the Dragon’s appendix describes is reached through an address the user has to know.
After Dragon Data
The Dragon 64 had less than a year with its original maker. In early 1984 GEC McMichael took over British sales and advertised it as the “GEC Dragon 64”, and in June Dragon Data called in the receivers. The Spanish company Eurohard, which bought the rights, told Dragon User in 1985 that it would concentrate on the Dragon 64 with disk drives as an entry-level business machine. The Dragon 32 entry follows that story.
Sources
- Duncan Smeed and Ian Sommerville, Inside the Dragon (Addison-Wesley, 1983), Appendix 5, pp. 333-339: design aims, the map type 1 overlay and bootstrap, the blue cursor, the lack of a way back, the checksum and RECSUM, the serial port and PRNSEL.
- Your Computer, January 1984, pp. 70-71: David Scobie’s review (the £229 price, the blue cursor, the extra free memory, OS-9 needing the 64, and the verdict).
- Dragon User, September 1983, pp. 19-21: Tano and the American Dragon 64. October 1983, p. 5: the first UK public appearance. December 1983, p. 22: Keith and Steven Brain’s benchtest. March 1984, p. 10: OS-9 in the shops, and p. 60, S.P. Electronics advertisement (£225). April 1984, p. 31: OS-9 review. May 1984, p. 3: GEC McMichael’s takeover of UK sales. June 1984, pp. 34-35: “GEC Dragon 64” advertisement. May 1985, p. 3: Eurohard’s plans for the Dragon 64.
- F. G. Swygert, Tandy’s Little Wonder: The Color Computer 1979-1991 (FARNA Systems, 1993): Tano’s price cut to $149.