CP/M running on Sinclair ZX Spectrum +3

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Unlike previous ZX Spectrum computers, +3 is equipped with an internal 3-inch floppy drive (compatible with Amstrad computers) and it is fully capable of running CP/M. The system runs snappier and more responsive than Commodore 128 in the CP/M mode but there are two caveats. Multiple keys are missing in the crippled keyboard layout and these are replaced with cumbersome keyboard shortcuts. This can be especially annoying when working with spreadsheets.

Another issue comes from the fact that the video circuit works in a resolution of 256×192 so it cannot handle the standard 80×24 text-mode typical for CP/M machines. The computer normally displays only 32 characters per row which would not be enough for any CP/M program. The +3 version of CP/M therefore uses a reduced font resolution with just 5×8 pixels for each character (including space between characters). Such font allows to display 51×24 characters and that’s the default text mode when +3 is booted in CP/M.

Of course not all programs work correctly with the reduced screen size so there is a program called SET24x80.COM. It provides a virtual 80×24 screen and you can quickly switch between displaying the first 51 columns or last 51 columns of the screen using a keystroke.

Expanded Sinclair QL

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This is my Sinclair QL setup. It is 0.9 meters wide when a 512kB RAM expansion, floppy controller and floppy drive are connected. You need a really big desk for this.

Sinclair QL, Motorola 68008 and Microdrive

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A friend of mine sent me one Sinclair QL in a big box with manuals and accessories (ROM modules, floppy controller, IDE controller, 512k RAM expansion, RS232 adapter) because I wanted to test it using our benchmark and compare the results with 8088 in PC and Motorola 68000 in Amiga 500.

Sinclair equipped the computer with Motorola 68008. The standard 68000 CPU has a 16-bit data bus, but this smaller version has it only eight bits wide. The rest is the same so there are 32-bit CPU registers and 16-bit ALU. Using the narrowed data bus was an understandable way to make computers cheaper. IBM PC 5150/5160 has also its data bus eight bits wide. On the other side Intel 8088, unlike Motorola 68008, has a small prefetch queue so there should be smaller performance loss in comparison with a standard version of the chip.

I’ve never done anything with Sinclair QL so this is my first time. I’m quite surprised that the keyboard is mechanically much better than the one on Sinclair Spectrum+ (which looks almost the same). Also two integrated Microdrive units are easy to use and surprisingly fast. Each tape can hold 100kB of data and having two drives allows for easy tape copy.