The Macintosh 512K Personal Computer, the second of a long line of Apple Macintosh computers, was the first update to the original Macintosh 128K. It was virtually identical to the previous Mac, differing primarily in the amount of built-in memory, which quadrupled the original's. This large increase earned it the nickname Fat Mac. The additional memory was significant because more ambitious users with computer experience stretched the capacity of the original Mac almost immediately, despite the limited number of applications.

Mac 512K with keyboard, mouse, external floppy drive	Mac 512K back panel
Introduced:	September 10, 1984
MSRP:	$2795
CPU:	Motorola 68000
CPU speed:	8 MHz
Shipped with system version:	1.1, later 2.0
RAM:	512 KB
Discontinued:	April 14, 1986

The applications MacPaint and MacWrite were still bundled with the Mac. Soon after this model was released, several other applications became available, including MacDraw, MacProject , Macintosh Pascal and others.

The LaserWriter became available for the first time shortly after the 512K's introduction, making home desktop publishing a possibility for the first time, although the LaserWriter's initial $6,995 price put it far out of the reach of most individuals.

An enhanced version of the Mac 512K debuted as the Macintosh 512Ke in April 1986. It differed from the original 512K in that it had an 800K floppy disk drive and more ROM.

The original 512K can accept Macintosh system software up to version 4.1; the 512Ke can accept up to System 6.0.8.