Although several non-English keyboard layouts are available, the Dvorak keyboard layout was never ported to the Lisa, though such porting had been available for the Apple III, IIe, and IIc, and was later done for the Macintosh. Keyboard-mapping on the Lisa is complex and requires building a new OS. All kernels contain images for all layouts, so due to serious memory constraints, keyboard layouts are stored as differences from a set of standard layouts; thus only a few bytes are needed to accommodate most additional layouts. An exception is the Dvorak layout that moves just about every key and thus requires hundreds of extra bytes of precious kernel storage regardless of whether it is needed.