The Sinclair QL (for Quantum leap), is a personal computer launched by Sinclair Research in 1984, as an upper-end counterpart to the Sinclair ZX Spectrum. The QL was aimed at the serious home user and professional and executive users markets from small to large businesses and higher educational establishments, but failed to achieve commercial success.
Based on a Motorola 68008 processor clocked at 7.5 MHz, the QL included 128 kB of RAM (officially expandable to 640 kB; in practice, 896 kB) and could be connected to a monitor or TV for display. Two built-in Microdrive tape-loop cartridge drives provided mass storage, in place of the more expensive floppy disk drives found on similar systems of the era. (Microdrives had been introduced for the Sinclair ZX Spectrum in July 1983, although the QL used a different logical tape format.) Interfaces included an expansion slot, ROM cartridge socket, dual RS-232 ports, proprietary QLAN local area network ports, dual joystick ports and an external Microdrive bus. Two video modes were available, 256×256 pixels with 8 out of 256 RGB colours and per-pixel flashing, or 512×256 pixels with four colours (black, red, green and white). Both screen modes used a 32 kB framebuffer in main memory. The hardware is capable of switching between two different areas of memory for the framebuffer, thus allowing double buffering. However, this would have used 64 KB of the standard machine's 128 kB of RAM and there is no support for this feature in the QL's original firmware. The alternative and much improved operating system Minerva does provide full support for the second framebuffer. When connected to a normally-adjusted TV or monitor, the QL's video output would overscan horizontally. This was reputed to have been due to the timing constants in the ZX8301 chip being optimised for the flat-screen CRT display originally intended for the QL.