of the 6502 processor as that allowed the clock to be stopped for this 40 microsecond period.) In other modes the CPU and video accesses are interleaved with each accessor acquiring bytes at 1 MHz. In contrast, the BBC Micro employs one or two sets of eight 16-kilobit devices, with the RAM running at twice the speed (4 MHz) of the CPU (2 MHz), allowing the video system (screen refresh) and CPU memory accesses to be interleaved, with each accessor able to transfer bytes at 2 MHz. The RAM access limitations imposed by the Electron's ULA therefore reduce the effective CPU speed by as much as a factor of four relative to the BBC Micro in the more demanding display modes, and as much as a factor of two otherwise. Byte transfers from ROM occur at 2 MHz, however. Hardware The hardware specification according to official documentation, combined with more technical documentation and analysis is as follows: CPU: Synertek SY6502A Clock rate: variable. CPU runs at 2 MHz when accessing ROM and 1 MHz when accessing RAM. The CPU is also periodically halted. Glue logic: Ferranti Semiconductor Custom ULA RAM: 32 KB ROM: 32 KB Graphics modes: 160×256 pixels (20×32 characters) in 4 or 16 colours, 320×256 (40×32 characters) in 2 or 4 colours, 640×256 (80x32 characters) in 2 colours Text modes: 40x25 characters in 2 colours, 80x25 characters in 2 colours Colours: 8 colours (TTL combinations of RGB primaries) + 8 flashing versions of the same colours Sound: 1 channel of sound, 7 octaves; built-in speaker. Software emulation of noise channel supported Keyboard: 56 key "full travel QWERTY keyboard" Dimensions: 16×34×6.5 cm I/O ports: Expansion port, tape recorder connector (1200 baud CUTS variation on the Kansas City standard for data encoding, via a 7-pin circular DIN connector), aerial TV connector (RF modulator), composite video and RGB monitor output Power supply: External PSU, 19V AC The composite video output provides a greyscale image on the standard machine, but an internal modification allows a colour image to be produced, albeit with a degradation in picture quality. Acorn ostensibly intended the composite output to be a high-quality output for monochrome monitors, with the RGB output being the preferred high-quality output for colour images. Quirks Like the BBC Micro, the Electron was constrained by limited memory resources. Of the 32 KB RAM, 3½ KB was allocated to the OS at startup and at