Sinclair ZX Spectrum +3
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The ZX Spectrum +3 looked similar to the +2 but featured a built-in 3-inch floppy disk drive (like the Amstrad CPC 6128) instead of the tape drive, and was in a black case. It was launched in 1987, initially retailed for £249 and then later £199 and was the only Spectrum capable of running the CP/M operating system without additional hardware.
The machine was a fairly big redesign over the +2, with new ports added, or changed. Probably the biggest difference was to the rear of the machine, which now sported an all new interface port for a printer and also for the allowance of a second disk drive.
Gone was the keypad port, Amstrad had never supported this with the +2, and even Sinclair had only released this officially in Spain, it was replaced by an auxiliary port, which was used by such things as the Cheetah light gun.
The RS232 socket was retained, and because the machine now required more power, and different voltage lines, a larger PSU, and a DIN socket on the machine were needed, this larger plug did prevent some peripherals from being attached. In addition to the handling the music and FX out of the machine, the sound socket now also allowed a cassette deck to connect, to load games from tape. The RF socket remained unchanged.
The left side of the machine also remained the same and contained the two Sinclair joystick ports and the reset button.
The disk drive uses 3.0 disks, not the industry standard 3.5, these disks and drive loaded quickly, and were reasonably reliable. In recent years, the drive belts perished, leaving a sticky residue on the capstans, this needed to be removed carefully, and a new belt fitted, great care must be taken not to lose the drive pin, if this happens the drive is left permanently in write mode.
The +3 saw the addition of two more 16 KB ROMs, now physically implemented as two 32 KB chips. One was home to the second part of the reorganised 128 ROM and the other hosted the +3's disk operating system. This was a modified version of Amstrad's AMDOS, called +3DOS. To facilitate the new ROMs and CP/M, the bank-switching was further improved, allowing the ROM to be paged out for another 16 KB of RAM.
Almost all +3 machines have a sound fault, due to a component being left off the board, which means the sound is distorted and clips.
The only models not to have the problem contain the 270835 motherboard, and only seem to appear in Spain.
Unfortunately for Amstrad, the machine's high cost, and games costing on average five pounds more on disk, sales of the computer and software were low, those who did buy the machine were happy enough to load cassette games in through the sound socket.
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This exhibit has a reference ID of CH509. Please quote this reference ID in any communication with the Centre for Computing History.
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