UK Computers 1978 to 1989
Another circuit board computer. This was built by Compukit of Barnet, North London and was initially a copy of the Ohio Superboard. Unfortunately, Ohio do not appear to have been too keen on this and it was about two years to resolve the wrangling and, by then, the Ohio was the better system. Never mind, the UK101 was British! This was also normally sold in kit form (for £249) and even the keys had to be soldered onto the circuit board. A popular, though dramatic, modification on some I have seen was to hacksaw off the keyboard and extend using soldered wires to the keyboard relocated onto a case with the remainder of the circuit board inside. Unlike the Nascom, the UK101 was based on the 6502 microprocessor which, in many ways, is the easier one to learn. This also had a "bug", this one being Cegmon though they could also be purchased with BASIC on board fitted to one of the spare EPROM sockets as many were. A standard purchase, including BASIC, would include a 1MHz 6502 processor, 8 KB of memory (expandable to 16 KB) and Cegmon plus BASIC. It could display on a standard television with 16 lines of up to 48 characters (though, in my experience) most televisions of that time were only able to display 40 characters on a line with any clarity. The UK101 could put less characters on a line so as to provide a decent display.
This picture is not one from my collection as I have still to track down a UK101.
This one is from my collection and shows the way it connected to a backplane board so you could connect to other circuit boards. The Nascom 2 differed in being a 4 MHz Z80 (twice as fast) though otherwise very similar.
This one is another jewel in my collection. The Microtan differed from the Nascom and UK101 in being quite a bit smaller. The others were based around a circuit board about the size of an A4 sheet of paper. The Nascom edge connector was across the whole width of the board with connections on both sides to carry all the necessary contacts. The Microtan was built much more compactly to about A5 size. It also had an edge connector but this was a proper plug and socket version with three rows of pins set much closer together making the additional width of the Nascom unnecessary.
The Microtan also used the 6502 microprocessor (clocked at 750 KHz so slower than the UK101), it produced 16 lines of 32 characters on a standard TV screen and came with 1 KB of memory (with half used for the screen display) and a 1 KB ROM containing TanBug. BASIC could not run on the standard Microtan as there was insufficient memory. Interestingly, the Microtan actually used a 1 MHz 6502 microprocessor but it used a single clock for both the processor and the screen refresh. The screen had to be refreshed at 6 MHz so, with no processor faster than 1 MHz, they had to divide the clock speed for the processor. Dividers all use binary (every other cycle, one in every 4, one in every 8 and so on) and 6,000 over 8 is 750.
Being a circuit board computer, and especially as many Microtans went into test equipment, Tangerine also produced a number of additional boards. The most popular (and one pictured) is the Tanex expansion board. This provided an extended "bug" called XBug, space for another 7 KB of memory (making it possible to run BASIC) and five EPROM sockets, into one of which could be placed a BASIC ROM. Other ROMs included an assembler though many contained specific software for test equipment.
A "mini-motherboard" connected the Microtan 65 board to the Tanex card. Also available (and shown) is a full system, motherboard able to be located in a case (then called a Micron) offering 12 sockets, one for the Microtan, one for the Tanex and 10 spare. Other boards produced were a memory board (with another 40 KB of memory) called Tanram (the designer was nothing if not predictable), an input output board to control external appliances, a disk controller offering an operating system called TanDos and a graphics board. Mine has only 4 sockets fitted which does not seem unusual. I assume the sockets were very expensive so why buy what you do not plan to use?
In kit form, the Microtan 65 cost over £100 so cheaper than the others though still a lot of money in its day.