in LocoScript), called +3DOS. These two new 16 KB ROMs and the original two 16 KB ROMs were now physically implemented together as two 32 KB chips. To be able to run CP/M, which requires RAM at the bottom of the address space, the bank-switching was further improved, allowing the ROM to be paged out for another 16 KB of RAM. Such core changes brought incompatibilities: Removal of several lines on the expansion bus edge connector (video, power, and IORQGE); caused many external devices problems; some such as the VTX5000 modem could be used via the "FixIt" device. Dividing ROMCS into two lines, to disable both ROMs. Reading a non-existent I/O port no longer returned the last attribute; caused certain games such as Arkanoid to be unplayable. Memory timing changes; certain RAM banks were now contended causing high-speed colour-changing effects to fail. The keypad scanning routines from the ROM were removed. Some older 48K and 128K games were incompatible with the machine. The ZX Interface 1 was incompatible due to differences in ROM and expansion connector, making it impossible to connect and use the Microdrive units. Unlike previous models, the ZX Spectrum +3 power supply uses a DIN connector and has "Sinclair +3" written on the case. The same power supply could also be used with the later +2A/B models. Production of the +3 ceased in December 1990, believed to be in response to Amstrad relaunching their CPC range. At the time, it was estimated about 15% of ZX Spectrums sold had been +3 models. Production of the +2B (the only other model then still in production) continued, as it was believed not to be in competition with other computers in Amstrad's product range. ZX Spectrum +2A The ZX Spectrum +2A was a new version of the Spectrum +2 using the same circuit board as the Spectrum +3. It was sold from late 1988 and unlike the original grey +2 was housed inside a black case. The Spectrum +2A/+3 motherboard (AMSTRAD part number Z70830) was designed so that it could be assembled with a +2 style "datacorder" connected instead of the floppy disk controller. Amstrad planned to introduce an additional disk interface for the +2A/+2B called the AMSTRAD SI-1, but it never appeared. If an external disk drive was added, the "+2A" displayed on the system menu text would change to "+3". The power supply of the ZX Spectrum +2A