Twenty-five years ago, Apple introduced the Macintosh Plus, a groundbreaking member of the Mac family tree. Industry analysts praised the Plus, which retailed for $2,599 (about £1,640) - or what would be a whopping $5,188 (£3,274) today - as the computer Apple should have released in 1984.

The Mac Plus introduced a number of significant enhancements to the Mac line and solidified the Macintosh as a viable platform. Before the Plus, people spoke of the Macintosh in terms of its potential—as it could be. After the Plus, people spoke of the Mac as it was.

More RAM, please

The original Macintosh that was released in 1984, the Macintosh 128K, was by all accounts a revolutionary machine. But it carried with it a few significant drawbacks. The most troubling came in the form of a mere 128KB of built-in RAM. Ambitious developers anxious to craft graphics-intensive applications quickly bumped up against that limit, severely restricting the complexity of early Mac software. The worst part is that Apple couldn’t help them: the company provided no authorized way of upgrading the Mac’s RAM.

Apple first gave the Mac series a memory upgrade with the Macintosh 512K (which included 512KB of RAM, natch) in late 1984. However, users could still not upgrade the RAM themselves. In contrast, the Mac Plus shipped with 1MB (or 1024KB) of memory, which provided ample breathing room for the hot new desktop publishing apps of the day. Even better, the Plus supported up to 4MB of RAM in the form of user-installable memory modules.

The Mac Plus’s expanded RAM opened the floodgates to a new generation of advanced Mac software that finally lived up to the platform’s fullest potential.

A pun that involves SCSI

As part of Apple’s vision, the first Mac was a fully self-contained “appliance” that, through its non-user-serviceable nature, theoretically made life easier for the user. In practice, computer users of the early 1980s were accustomed to opening their PCs and adding all sorts of goodies to push systems to their limits. The Mac’s closed nature (combined with its limited RAM) frustrated those types to no end.

The first Mac contained no high-speed general-purpose peripheral expansion bus of any sort; only a floppy drive port, two serial ports, and a mouse port. Aftermarket upgrades connected either through add-on boards that plugged directly into the CPU socket on the motherboard (yikes!) or through a Rube Goldberg-like utilization of the floppy, mouse, and serial ports in tandem. Apple’s first Mac hard drive, an external unit, plugged into the floppy port. You can probably imagine how slow it was.

With the Mac Plus, Apple began the foot-dragging process of officially opening up the Mac to outside peripherals. It did this through the inclusion of the Mac line’s first ever SCSI (pronounced scuzzy) port. SCSI was (and is) an industry-wide interface standard that allowed a diverse array of peripherals to be connected to the Mac. (In this case, only externally—Apple was only willing to go so far.)

As one of the earliest, most-prominent examples of including the SCSI standard in a 1980s personal computer, the Mac Plus seeded a vibrant new market for SCSI-based peripherals, much like the iMac did with USB in 1998. While most of the peripherals were hard drives, enterprising companies produced Mac-tailored SCSI devices as varied as tape drives, ethernet adapters, and even SCSI-based graphics cards that allowed for a color display.

In other words, the Macintosh Plus wasn’t just what came in the box. You could add on to it without voiding your warranty.

New and improved keyboard

The Plus shipped with an extended keyboard that included, for the first time, both an integrated numeric keypad and arrow keys for cursor navigation. Even something as seemingly minor as arrow keys (which Steve Jobs insisted on omitting from the first model to force software developers to use the mouse) opened the Mac up to a whole new world of less-annoying business productivity software. Imagine navigating a spreadsheet app without cursor keys, and you’ll see why.

Twice the floppy space

The original Mac included a built-in single-sided, double density floppy drive that stored 400KB per disk. Developers found 400KB limiting in the graphically rich Mac realm and software soon began shipping in multiple-disk sets. The Mac Plus partially alleviated that problem by shipping with a double-sided, double-density drive that could handle 800KB per disk.

Russian nesting folders

The inclusion of SCSI in the Mac Plus meant that many more users would be storing data on external hard drives. The original Macintosh File System (MFS) had some significant limitations that weren’t too severe in the world of 400KB disks, but suddenly became problematic with 20-plus megabyte hard drives. Most significantly, MFS didn’t support volumes over 20MB total. It also didn’t support nesting folders, and it stored its file directory in an inefficient and slow-to-access manner that didn’t lend itself to hard disks full of thousands of files.

Enter HFS, or Hierarchical File System, which solved these problems and more. HFS made its debut with System 2.1 in 1985, but it took up precious RAM space in the Macintosh 512K when loaded up at boot time. With the Plus, Apple moved the HFS code to ROM and added several improved graphics routines to further spiffy up the system. HFS in ROM was an important step to usher in the next era of Macintosh file storage.

Unmatched longevity

With all these improvements, the Mac Plus sold well, and it remained Apple’s best-selling model even after the introduction of the Mac SE in 1987. As Apple introduced newer models in the Mac line, the company continued to discount the Mac Plus, positioning it as the lowest-end Mac until the Macintosh Classic debuted in 1990. The venerable Mac Plus continued to see heavy use in the real world far beyond its astounding 4.5-year production lifespan. No other single Mac model has been produced for that length of time.

Many of those same Mac Plus machines were so well built that most of them still work today. If you have one of these living relics resting in your garage or attic, this may be a good time to dust it off, fire it up, and drink a 25th anniversary toast to the machine that truly made the Macintosh platform sing.

Benj Edwards is a freelance writer who specializes in computer and video game history. He is also editor in chief of Vintage Computing and Gaming, a blog devoted to vintage technology.