Macintosh 128k and 512k
The Macintosh 128k was the original model of Macintosh. The Macintosh 512k is identical aside from having more memory.
Specifications
| Spec | Macintosh 128k | Macintosh 512k |
|---|---|---|
| Release Date | January 1984 | September 1984 |
| Discontinuation Date | October 1985 | April 1986 |
| Processor | Motorola 68000 @8MHz | |
| RAM | 128KB DIP Memory | 512KB DIP Memory |
| Hard Disk | None | |
| Display | 9-inch Monochrome CRT Display @512x342 | |
| Audio | Internal Speaker | |
| Internal Drives | Auto inject 3.5" 400KB Floppy Drive | |
| Expansion | None | |
| Networking | None | |
| Other I/O | - 2x Serial - 1x External Floppy Port - 1x Keyboard connector - 1x Mouse connector - 1x Line Out |
|
| PRAM Battery | PX21 4.5V Alkaline | |
| Original Mac OS | System Software 0.97 | System Software 1.0 |
| Maximum Mac OS | System Software 3.2 | System Software 4.2 |
Upgrades
CPU Upgrades
Faster 68000, 68020, and 68030 upgrade boards were made for the original Macintosh.
Memory Upgrades
Many, many Macintosh 128ks were upgraded to 512k, either by Apple or by third parties. Aftermarket RAM upgrades could take you higher than that as well.
Floppy Drive Upgrades
Another extremely common 128k/512k upgrade was an 800K floppy drive upgrade. This upgrade involved replacing the floppy drive and system ROMs with those from a Macintosh Plus.
SCSI Upgrades
Aftermarket upgrades were made available for the original Macintoshes that added a SCSI port. As such, you can rarely find original Macs that have been upgraded with 1MB of RAM, SCSI, and an 800K floppy drive, effectively turning it into a Mac Plus.
Resources
 Service Manual |
 Schematics |
|---|
Common Faults & Maintenance
PRAM Battery Leaks
The Alkaline PRAM battery in the original Macintosh is very prone to leaking and should be removed. It is located behind a door on the back of the system. A leak can cause damage to the analog board it is attached to.
Capacitors
This Mac's capacitors have held up pretty well over time, but they're old enough now that the analog boards often need recapping. The logic board rarely has capacitor trouble.
No Video Defect
Due to having no internal fan, the Macintosh gets pretty toasty when its running. This often causes the larger solder joints on the analog board to crack, causing a no video defect. I would recommend reflowing the large solder joints on the power connector and flyback transformer even if your Mac works fine, for additional stability.
Page last updated (MM/DD/YYYY): 03/03/2025
Update Reason: page created
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