Apple II Language Card
The Apple II Language Card was a popular expansion card for the first home computer Apple II , which in its ROM - address space by bankswitching optional RAM -Speicher could show. This enabled a memory expansion of up to 64 kB. The card was originally only sold together with extension languages, for example with Apple Pascal and Apple FORTRAN. However, replicas of the card by other companies were soon available without such language packs, and from around 1982 many Apple programs required such a card.
technology
The 6502 microprocessor in the Apple II had a 16-bit address space, so it was only able to address 64 kB of memory. The Apple II used up to 48 kB of this address space for RAM memory, followed by 4 kB in which I / O addresses for memory mapped I / O and the ROMs on expansion cards were accommodated. The upper 12 kB were reserved for the built-in ROM of the Apple II (10 kB for the BASIC interpreter, 2 kB for the actual operating system).
When accessing certain I / O registers, the language card was displayed in the address space instead of the 12 kB of the ROM. The first 4 kB could be switched between two memory banks using a second level of bank switching , so that the card offered a total of 16 kB. Other manufacturers used the same principle to display additional 4 KB blocks in the address space and thus achieve significantly more than 64 KB total memory.
By default, the card was always inserted in slot 0 (far left). In principle, it also works in the other slots, but almost all programs, including the Apple DOS and Apple ProDOS operating systems , expect the card in slot 0.
The Language Card offered by Apple itself also contained a ROM chip, the content of which was identical to the so-called Autostart ROM of the Apple II + . This also gave the original Apple II model the ability to automatically start an operating system or other program from a floppy disk when it was switched on without entering a command. The replicas of the Language Card offered by other companies did not use this ROM chip due to copyright reasons; on the now much more common Apple II +, this brought no additional benefit anyway.
In the further developed Apple IIe computer model and all later models in the series, a memory expansion similar to the language card was already built in. Slot 0 was omitted, so that only seven standard Apple slots (1–7) were available.