by the unit, with such drives needing to provide a Shugart-compatible connector and their own power supply. The original Electron edge connector was repeated on the back of the Plus 3, allowing the Plus 1 or other compatible expansion to be connected in conjunction with the Plus 3. The double-density drive of the Plus 3 was driven using a WD1770 drive controller by the ADFS. (The Plus 3 had been rumoured to offer Acorn's DFS and to feature a 8272 double-density disk controller before its launch.) Because the WD1770 is capable of single-density mode and uses the same IBM360-derived floppy disc format as the Intel 8271 found in the BBC Micro, it was also possible to use the Disc Filing System with an alternate ROM, such as the ACP 1770 DFS. The Plus 3 reset PAGE to &1D00, reducing the amount of free RAM available to the user. The ADFS system could be temporarily disabled (and PAGE reset to &E00) via the command. Later products such as the PRES E00 ADFS remedied the memory demands of the ADFS, along with other issues suffered by the software as delivered with the Plus 3. If using the Plus 3 in screen modes 0–3, the pseudo-variable would be thrown off, as the interrupts were disabled during disk access in these modes. The screen would also blank during disc accesses. Disks had to be manually mounted and dismounted using the / commands, or using the ++ key combination. Disks could also be booted from via the standard + key-combination, if the !BOOT file was present on the disk. This behaviour was the same as on the BBC Micro. The Plus 3 included an uprated square black power supply unit with mains cord, manufactured by STC, designed and manufactured in England to and , that was designed to power the Plus 3, in addition to the Electron and the Plus 1 interface as well. This replaced the original cream-coloured "wall wart" style power supply, designed to and manufactured in Hong Kong. Original Part no: 0201,113; input 220/240 V AC/50 Hz; output 19 V AC/0.737 A/14 W: Usage: Electron, Electron+Plus1 Uprated Part no: 0865,010; input 240 V AC/50 Hz 50 W; output 21 V AC/1.75 A/36.75 W: Usage: Electron+Plus3, Electron+Plus3+Plus1 Repair note: If the internal power-supply connector, used to power the existing internal 3.5-inch drive is damaged, and requires replacement, then the original AMP 800-930 4-pin