680x0

   A family of 32-bit microprocessors from Motorola, used in Macintosh computers and many advanced workstations. The 680x0 is popular with programmers, because it uses a linear-addressing mode to access memory, rather than the segmented-addressing scheme used by Intel coprocessors.

   Several models have been developed:

   • 68000

   The first microprocessor in this family, which used a 32-bit data word with a 16-bit data bus and could address 16MB of memory. It was used in the first Apple Macintosh computers as well as in Hewlett-Packard's LaserJet printers.

   • 68020

   A 32-bit microprocessor that runs at 16MHz, 20MHz, 25MHz, or 33MHz and is capable of addressing as much as 4GB of memory. The 68020 was used in the Macintosh II computer, but has been replaced by the 68030.

   • 68030

   Has a paged memory management unit built-in and, therefore, does not need external hardware to handle this function. The 68030 is used in the Macintosh II and SE computers.

   • 68040

   Incorporates a built-in floating point processor and memory management unit, along with independent 4KB data and instruction caches. It can perform parallel execution by using multiple, independent instruction queues. The 68040 is used in the Macintosh Quadra line of computers.

   See also PowerPC.