The Compukit UK101 microcomputer (1979) is a kit clone of the Ohio Scientific Superboard II single-board computer, with a few enhancements for the UK market - notably replacing the 24×24 (add guardband kit to give 32×32) screen display with a more useful 48×16 layout working at UK video frequencies. The video output is black and white with 256 semigraphic characters generated by a two kilobyte ROM. It has no bit-mapped graphics capability. The video is output through a UHF modulator, designed to connect to a TV set. History The UK101 design was published in Practical Electronics, a popular hobbyists magazine at the time. The August, September, October and November 1979 issues carried the four parts of the article, by Dr. Anthony A Berk. Later issues of the magazine contained information on modifications and additions to the machine, including a series of articles on building an expansion unit. Kits of parts for building the machine were available from Compukit Ltd. / CompShop Ltd. of 14 Station Road, Barnet, Hertfordshire. It is thought that around 5000 kits were produced. Description Processor The Compukit UK101 is powered by a 6502 microprocessor CPU running at 1 MHz, and is equipped with up to 8 kilobytes of RAM using 2114 static RAM chips of 1024×4-bit. An additional memory-mapped 1 KB of RAM is used for the video display. It has the 8K Microsoft BASIC interpreter stored in ROM. In addition to Basic, a 6502 machine code monitor (2K bytes) is built into ROM. It allows programming by entering sequences of 6502 opcodes. Later a two-pass assembler was available which allows the use of assembly language. Although the 6502 has two interrupt input pins (NMI and IRQ), neither is used by the UK101. Display The UK101 has a 16-row, 48-column memory-mapped character semigraphics display, with each character taking up 8x8 pixels with an aspect ratio of about 1:2 (corresponding to an effective resolution of 384x128). All scrolling and character output functions are handled by firmware. In the original ROMs, the output functions were rudimentary and did not include a clear-screen function. CPU access to video memory causes noticeable glitches (known as "snow") on the screen. Keyboard The keyboard of the UK101 is located on the main PCB, and comprises a matrix of keyswitches. The matrix is interfaced to the CPU via two 8-bit I/O ports, and is polled by firmware in the machine's ROMs. One key