The Macintosh 512K was the successor of the Macintosh 128K (or simply Macintosh) and introduced by Apple Computer in 1984. The machine was nicknamed "fat Mac" because of it's larger memory, 512KByte. The machine was however technically different from the original Macintosh. It had a completely redesigned logic board to easily accomodate both 128KByte and 512KByte RAM during manufacturing. The new design allowed for easier upgrades of the Macintosh 128K.
The increased memory allowed for more powerful applications, such as the popular Microsoft Multiplan spreadsheet application. The other specifications were similar to the original Macintosh