Apple Macintosh 512K

Released 1984: The Macintosh 512K is a personal computer that was designed, manufactured and sold by Apple Computer, Inc. from September 1984 to April 1986. It is the first update to the original Macintosh 128K. It was almost identical to the previous Macintosh, differing primarily in the amount of onboard memory. The increased memory gained the ability to run more advanced software and turned the Macintosh into a more business-capable computer. It’s the earliest Macintosh model that can be used as an AppleShare server.


  • Type: All-in-one
  • Manufacturer: Apple Computer
  • Product family: Compact Macintosh
  • Released: September 10, 1984
  • Discontinued: April 14, 1986
  • OS: System 1.1 – 4.1
  • Introductory price: $4369 (1 MB RAM, no hard disk)
  • CPU: 68000 @ ~¨8 MHz (effectively 6 MHz)
  • Memory: 512 KB RAM
  • Graphics: 512 x 342 pixel, 1 bit
  • Audio: 8-bit mono 22 kHz
  • Display: 9″ black and white CRT
  • Storage: 3.5″ FDD, single side (400 KB)
  • ROM 64 KB
  • Dimensions: 13.6″ x 9.6″ x 10.9″
  • Weight: 16.5 lb (7.5 kg)
  • Predecessor: Macintosh 128K
  • Successor: Macintosh Plus, Macintosh 512Ke

The Mac 512K originally shipped with Macintosh System Software 1.1 but was able to run all versions of MacOS up to System 4.1. It was replaced by the Macintosh 512Ke and the Macintosh Plus. Support for the Mac 512K was discontinued in 1998.

Like the Macintosh 128K before it, the Macintosh 512K contains a Motorola 68000 running at 7.8 MHz and has a 16-bit data bus. Though the memory had been quadrupled, it could not be upgraded. The large increase earned it the nickname Fat Mac. The video controller used 22 KB of the system RAM and shares the data bus. This design reduces CPU performance up to 35%.

It shared a revised main board with the re-labeled Macintosh 128K, previously just called the Macintosh. This streamlined manufacturing.

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. Microsoft Excel was first written specifically for the Macintosh and required at least 512 KB RAM, but helped the Macintosh being seen as a serious business computer.

Apple Macintosh with Steve Jobs
Steve Jobs with an Apple Macintosh 128K or 512K in his lap.

Macintosh 512K enhanced
An updated version replaced the Macintosh 512K and debuted as the Macintosh 512K enhanced in April 1986. It had an 800 KB floppy disk drive and the same improved ROM as the Macintosh Plus. With the exception of the new model number “M0001E”, they were otherwise cosmetically identical. The stock 512K could also use an 800 KB floppy disk drive as well as the Hard Disk 20, the first hard disk manufactured by Apple exclusively for use with the 512K, but required a special system file (not required by the 512Ke) that loaded the improved ROM code into RAM, thus reducing the RAM available for other uses. Apple offered an upgrade kit which replaced the floppy disk drive and ROMs, essentially turning it into a 512Ke.

My Macintosh 512K and repair

My Macintosh 512K turned on booted from the floppy disk drive. But it had some issues. There was some distortion in the upper area on the screen, the motorized floppy eject function didn’t work, there was two stuck keys on the keyboard and space-bar didn’t worked at all. It’s a US model, so I also need to use a 220 VAC to 110 VAC converter to use it.

Macintosh 512k in my collection
Macintosh 512k in my collection
  • Keyboard: I’ve removed some key-caps in the problem area and cleaned out, that solved the problem with stuck keys. I then split the keyboard open to get to the PCB and de-soldered the non-working microswitch for the space-bar. I was lucky enough to have a spare keyboard that already previously has been used for parts, and I removed a microswitch from that keyboard to use in this one. Keyboard then worked 100%.
  • Screen: I’ve split the machine open and  re-soldered the components on the screen analog board that is known to turn bad over the years, like the connector for the cable to the main board, and the flyback transformer. That seems to have solved the problem with disturbance on the screen.
  • Floppy drive: I’ve cleaned the reader head carefully with alcohol as usual. Cleaned out the dust in the drive mechanism, lubricated moving part for smooth action. I removed and opened the eject mechanism motor from the drive. The problem with floppy eject was one small bad gear in the mechanism. Over the years, that particular gear is known to get very fragile. It’s possible to get 3D printed replacements. I had a broken high density floppy drive for a much newer Mac model sitting around. I opened up the eject mechanism in that one to see if there was a similarity. To my surprise, those parts looked exactly identical to my older drive, so I could replace the broken gear. My 512K machine can now eject disks. 

Macintosh 512K

Remi Jakobsen

I'm collecting classic computers and video games, stretching from the 70's into the 90's. Restoration, history, usage ...

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