Logical logic board

The snap-apart, Logo-like constriction of the Portable extends all the way down to its logic board, which is housed in a plastic cage that snaps out of the case bottom after a bit of prying.

Nestled below the cage that holds the battery and drives lies the logic board (click to enlarge)

Flip that cage over, and out snaps the logic board. On that board you'll find the four expansion slots, clearly labled — as is practically everything else on the board. These four are the aforementioned modem slot, one RAM and one ROM slot, and a processor-direct slot (PDS), a CPU-specific slot that gave, as its name suggests, direct and speedy access to the processor.

As neatly labled as if it were to be used as an instructional device (click to enlarge)

The Portable's CPU is a low-power 16MHz Motorola 68HC000 running on a 16MHz system bus — well, both actually run at 15.6672MHz, if you want to be precise. That may sound dog-slow, but the popular Macintosh SE, which lived from March of 1987 through October of 1990, had an 8MHz 68000 on an 8MHz bus.

The $6,500 Macintosh SE/30 — one of the finest li'l machines Apple ever put out — debuted in January 1989, also with a 16MHz processor and bus. However, the SE/30, as its name suggests, used the far more capable Motorola 68030, a processor that would have sucked the Portable's battery dry in a nanosecond. Well, not literally, but you get the idea.

32-bit internal registers, a 24-bit address bus, and a 16-bit data bus (click to enlarge)

One megabyte of RAM was soldered onto the logic board in an array of thirty-two 32KB 8-bit static RAM chips. If you happened to be dripping with cash, you could add another four megabytes to its RAM slot, or another eight using its PDS.

Here's what one megabyte of static RAM looked like in 1989 (click to enlarge)

Those then-capacious RAM levels had to wait, however, until RAM densities improved. When the Portable first shipped, Apple offered only a one-megabyte RAM expansion card ($650), and third-parties hadn't yet weighed in. By the time the backlit model shipped, Apple also offered a three-megabyte card.

The PDS slot could theoretically have also supported other add-in cards providing functions such as Ethernet, but we're not aware of any such cards ever hitting the streets.

As we mentioned, the logic board is exceptionally well labeled — but we were still unable to figure out the function of one grouping of chips, gathered on their own individual mini-board:

We're thinking power management, but we're not sure — any help? (click to enlarge)

This oddity is labled "Hybrid", and its location near the power and reset switches make us think it may have something to do with power management. Any help from perspicacious Reg readers would be welcome.

The Macintosh Portable was eventually killed off in October 1991, just two years after it appeared. It was never a great success, and often shows up on "worst ever" lists, not only of Macs but also of personal computers in general.

We disagree, and hold it a in bit higher esteem due to its crisp display, long battery life, excellent keyboard, easy serviceablity, simple expansion, and inventive configurability.

However, it must be admitted that your humble Reg reporter is over six feet tall, weighs around 200 pounds, and didn't have to pay for his Macintosh Portable.

As we said earlier, context is all. ®

Bootnote

After receiving his Macintosh Portable mere days after its release, your reporter took it on a business trip, where he conspicuously showed it off in true "Look what nifty tech I have and you don't" geek form by using it in a hotel lobby with it resting directly on his lap.

When he tried to get up to leave, however, he discovered that the nearly 16-pound laptop had put both of his legs to sleep. Pride goeth before a fall, and all that.

All photography by the author