The Sinclair Spectrum +3 is the successor of the Spectrum +2, marketed one year earlier.
Just like the Spectrum+2 is a mix between the Spectrum 128 and the Amstrad CPC-464, the Spectrum +3 is a mix between the Spectrum 128 and the Amstrad CPC-6128. Indeed it has 3’’ disk-drive built-in the right-hand side of the case and a « real » full-stroke keyboard, just like the CPC-6128.
After the launch of the first Amstrad « Sinclair computer », the Spectrum +2, they redesigned the motherboard and the content of the ROMs to produce the Spectrum +2A/B and +3. They also made some internal changes on the bus and removed the keypad scanning routines of the Spectrum 128 and +2 (remember the keypad sold with the Spanish Spectrum 128k).
As on the Spectrum +2, two BASIC versions are implemented : the 48k BASIC to remain compatible with the original Sinclair Spectrum, and the 128k BASIC which was already introduced with the Spectrum 128.
As with the others 128k models, and due to the limitations of the Z80 CPU which can only address 65536 bytes, the 128kb RAM is not directly usable (unless with bank-switching routines), but can be used as a RAM disk (drive M :).
So, the big change is the built-in 3’’ disk drive, exactly the same as the CPC-6128’s drive. The operating system is called +3DOS and was developed by Locomotive Software Ltd who also conceived the CPC Basics and OS. So, of course, the +3DOS is very close to the CPCs disk operating system. The Amstrad FD-1 external drive can even be used with the Spectrum +3 as a second disk drive by connecting it directly to "DISK B PORT" at the back of the system.
The Spectrum +3 is considered the ultimate Spectrum model, gathering all the good points of the previous spectrum machines : 128k, convenient full-stroke keyboard, 3’’ built-in disk drive, 128k Basic, RAM disk, many interfaces... But sadly it was launched too late, at a time where the ST and the Amiga were already fighting on the shelves. It was the last official Sinclair Spectrum model ever made. The +2A and +2B models vere launched a little later, but were just a revision of the +2 model already marketed.
ZX SPECTRUM +3
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48K Spectrum BASIC (compatibility mode) and 128K Spectrum ZX+3 BASIC, integrated with +3 DOS