Editing Macintosh II (section)

=== Expansion Capabilities ===

The Macintosh II's defining characteristic was its six [[NuBus]] expansion slots, making it the first truly expandable Macintosh. NuBus, originally developed at MIT and refined by Texas Instruments, provided a 32-bit, processor-independent expansion bus running at 10 MHz. Each slot could theoretically transfer data at 40 MB/second, though real-world performance was typically lower due to arbitration overhead and system constraints.

The NuBus architecture was self-configuring, implementing an early form of plug-and-play functionality. Each card contained a declaration ROM that the system would read during startup, automatically configuring interrupts, memory mapping, and driver loading. This eliminated the need for DIP switches or jumpers common on IBM PC-compatible systems of the era.