September 10, 1984: Apple ships the Macintosh 512K, the first upgrade to the first-gen Macintosh 128K.

Coming less than eight months after the original Macintosh, the 512K Mac makes no sweeping changes to the computer’s form factor. Instead, the big upgrade is quadrupling the RAM. This leads Apple fans to refer to the computer as the “Fat Mac.”

Macintosh 512K appeals to more than early adopters

Apple had good reason to rush the 512K Mac to market, even though the first Mac actually exceeded Steve Jobs’ early sales forecasts. Apple sold 72,000 Macintosh 128K models in the first 100 days, rather than the expected 50,000. However, these buyers proved different from longer-term customers.

The first wave of Mac buyers — early adopter Apple loyalists — happily put up with an underpowered computer simply because of the excitement of owning a new product. After these customers bought their Macs, however, sales stalled. Apple needed an upgrade to address the first-gen Mac’s perceived failure regarding its lack of internal memory.

This perception hurt Apple, particularly when it came to cracking the business market, a sector dominated by IBM computers. Tools like Microsoft Excel, initially available only on the Macintosh, helped target businesses. However, it required a more powerful computer than the first-gen Macintosh. The shortage of RAM also plagued many other third-party developers.

Fat Mac aims at the business market

Thanks to Mac engineer Andy Hertzfeld’s Switcher program, the Fat Mac could load up to four programs at once. It could also switch between them (what we know refer to as “multitasking”). It accomplished this by partitioning the 512K memory into four separate 128K modules. A Fat Mac owner essentially got four computers in one, each running a single program. Prior to this, multitasking was something only Apple’s business-focused Lisa computer could do.

Finally, the Mac 512K arrived on the market at around the same time as Apple’s LaserWriter printer. The groundbreaking laser printer helped make the case for the Macintosh as a serious business computer.

It didn’t entirely work as a strategy. However, for those who used it, the Fat Mac was a great Macintosh — albeit one that couldn’t be upgraded any more than the first-gen model could.

The Fat Mac sold for $3,195, making it around $700 pricier than the Macintosh 128K. Apple replaced it a couple years later with the Macintosh 512Ke, which upgraded the 400K disk drive of the first two Macintosh computers with one that supported 800K floppies.

Did you own a Macintosh 512K? What was the first Macintosh you owned? Leave your comments below.