 The logic board is not compatible with the ROM-based firmware update (introduced some years later) and most newer plug-in expansion-slot cards.Shortly after the "Revision A" motherboard's release in 1983, engineers discovered that the bank-switching feature (which used a paralleled 64 KB of RAM on the Extended 80-Column Card; or 1 KB to produce 80 columns using bank-switching) could also be used to produce a new graphics mode, Double-High-Resolution, which doubles the horizontal resolution and increases the number of colors from the 6 of standard High-Resolution to 16.In order to support this, some modifications had to be made to the motherboard, which became the Revision B.