The Macintosh 512K was the first "Power" Macintosh. Introduced in September 1984 as a second system in the Macintosh line, the 512K soon replaced the original Macintosh. After the introduction of the Macintosh 512K, the original Macintosh was re-labeled "Macintosh 128K" to differentiate it from the Macintosh 512K. The Macintosh 128K was discontinued in 1985. The 512K continued in production until 1986, when it was replaced by the more capable Macintosh 512Ke.
Macintosh 512K back label
The 512K is virtually identical to the Macintosh 128K, differentiated mainly by the amount of built-in memory. The 512K or "Fat Mac" has 4 times the amount of built-in RAM of the original Macintosh. The increase in RAM from 128K to 512K, which was initially looked upon as a luxury by many pundits, soon became a necessity. Mac OS, unlike other operating systems in the 1980s, was particularly top-heavy with significant overhead devoted to its slick user interface that left precious little memory for applications. Developers found it difficult to develop software for the original Macintosh because of its limited RAM.
This problem was not anticipated by Steve Jobs, who insisted that 128K was sufficient for the Macintosh. Apple developers and engineers knew better, and saved Jobs from himself by building in a way to increase the RAM on subsequent Macs of the same form factor. Many of the upgrade products offered by early Mac third-party vendors centered on RAM upgrades for the original Macintosh.
The Macintosh 512K uses the same 400K disk drive as the original Macintosh. In early 1984, 400K was a large amount of storage. By late 1986, it was considered insufficient for powerful Mac applications. The 512Ke, which replaced the 512K in 1986, addressed this issue. The 512Ke supported 800K floppies. The primary upgrade path for the 512K is to swap its motherboard with a 512Ke. I considered doing so with my 512K, but what is really the point? The 512Ke offers the same capabilities of the 512K with the exception of the floppy drive. Both computers do not support SCSI and thus hard drives are hard to come by. Third-party vendors offered hard drives that connected to the floppy disk port, the modem port, or the printer port, but these were typically very slow, just like the floppy drive they replaced.
Macintosh 512K does not have an internal fan. Vents on the top help keep it cool.
But what is really the point of upgrading this antique computer? I already own a much more capable Macintosh Plus. The Plus offers more RAM (up to 4 MB), SCSI support, and 800K floppy support. Because of port differences, a Plus board will not fit in a 512K case. However, you can swap out the back case for a Plus case, plug the board into the 512K front, and replace the 400K floppy drive with an 800K floppy drive. Basically, you would have a Plus with a 512K front. But again, what is the point?
I consider this computer to be a collector's item. It is interesting in that it is an early Mac, but it just lacks that certain combination of ingredients (800K floppy and SCSI support) to give it that long-lived life span that was enjoyed by the Plus and SE. In order to use the machine, I need to move software to 400K floppies of which I have only a handful. Unlike 800K floppies, 400K floppies had a short production run in the 1980s and thus are somewhat difficult to find.
400K or Singled-Sided/Double-Density (SSDD) disks use the same magnetic field as 800K Double-Sided/Double-Density (DSDD) disks. The only difference is that drives that can use 800K disks have the ability to read both sides of the disk. A 400K disk can only be formatted on one side. An 800K disk can be formatted on both sides in an 800K drive or Floppy Drive/High-Density (FDHD), 1.4 MB drive that supports double-density disks. However, it is possible to use an 800K disk in the 512K's 400K internal disk drive. The 512K will treat a DSDD disk as a 400K disk and utilize only one side of the disk. If you then use that same 800K disk in an 800K or FDHD drive, you might have issues, especially if you then try to use it again in your 512K's 400K drive. It is best to use real 400K disks, but 800K disks will work. However, we advise against using a DSDD disk formatted on one side in a 512K to move data to another Mac with an 800K or FDHD drive if you can avoid it.
The 512K has the following ports: a DB-19 floppy drive port, a printer port, a modem port, a DB-9 mouse port, and speaker port. The 512K does not have an ADB port. The ports are labeled by icons representing their respective functions, a nice touch and testament to the Mac's ease of use philosophy. The keyboard uses an odd connector similar to a telephone RJ-11 connector (although not the same and not compatible). The keyboard is the original Macintosh compact keyboard that does not have function keys, a numeric keypad, or arrow keys. Apple explicitly left out the arrow keys in order to encourage users to depend on the mouse. Many industry pundits were stuck on this omission. They also decried the Mac's lack of compatibility with IBM software. Thankfully, Apple broke from this myopic mentality, offering up a suburb system with a new remarkable graphical operating system.
Macintosh 512K ports
Macintosh 512K keyboard
I have more than one system disk. The 512K does not have an internal hard drive and so the version of Mac OS I am using at any given time depends on the disk I have inserted in the floppy drive. The 512K is compatible with every version of Mac OS up to version 4.1 (Finder Version 5.5). Below are screen shots of two early versions of Mac OS. The first is Finder version 1.1g from 1984. The second is Finder version 5.3 from 1986. Also included below is a screen shot of MacPaint version 1.5 from 1985.
I purchased my 512K from a seller living in my area for $75 in 2006. The 512K originally cost about $2795. It is in great shape, but it does not have the 4.5V Alkaline, Type #523 battery. The Macintosh 128K, Macintosh 512K, Macintosh 512Ke, and Macintosh Plus all have this user-accessible battery, which can be replaced by removing a cover located over the power button on the back of the computer. The screen is in great shape and has no burn in. The 9-inch screen is capable of a single resolution, 512 x 384. It displays black and white pixels and is not capable of true gray scale.
Macintosh 512K battery panel
I don't intend to use this computer much. It is basically a museum piece. I really like the look of these original Macs. For anyone wanting to do more with an early Macintosh but still wanting to use this fan-less form factor, I would suggest buying a Macintosh Plus. In terms of what you can do with it for its age, the Plus is clearly superior.