It had a new 3.5-inch double-sided 800 KB floppy drive, offering double the capacity of previous Macs along with backward compatibility. The new drive was controlled by the same IWM chip as in previous models, implementing variable speed GCR. The drive was still completely incompatible with PC drives. The 800 KB drive had two read/write heads, enabling it to simultaneously use both sides of the floppy disk and thereby double storage capacity.
The Mac Plus was the first of many Macintoshes to use SIMMs (single in-line memory modules) for its memory. It came standard with 1 MB of RAM (four 256 KB SIMMs) and could be upgraded to 4 MB of RAM. It had 128 KB of ROM on the motherboard, which was double the amount of ROM that was in previous Macs; the new System software and ROMs included routines to support SCSI, the new 800 KB floppy drive, and the Hierarchical File System (HFS), which used a true directory structure on disks (as opposed to the earlier MFS, Macintosh File System in which all files were stored in a single directory, with one level of pseudo-folders overlaid on them). For programmers, the fourth Inside Macintosh volume detailed how to use HFS and the rest of the Mac Plus's new system software. This new filing system allowed it use the first hard drive Apple developed for the Macintosh 512K, the IWM floppy disk-based Hard Disk 20 and the new ROMs allowed the Macintosh to use the drive as a startup disk for the first time. The Plus still did not include provision for an internal hard drive and it would be over 9 months before Apple would offer a SCSI drive replacement for the slow Hard Disk 20. It would be well over a year before Apple would offer the first internal hard disk drive in any Macintosh.
A compact Mac, the Plus had a 9-inch 512 by 342 pixel monochrome display with a resolution of 72 PPI, identical to that of previous Macintosh models. Unlike earlier Macs, the Mac Plus's keyboard included a numeric keypad and directional arrow keys, and, as with previous Macs, it had a one-button mouse and no fan, making it extremely quiet in operation.
The applications MacPaint and MacWrite were bundled with the Mac Plus. After August 1987, HyperCard and MultiFinder were also bundled. Third-party software applications available included MacDraw, Microsoft Word, Excel, and PowerPoint, as well as Aldus's PageMaker. This was the first time GUI versions of Microsoft Word, Excel, and PowerPoint were introduced on any personal computer platform.
Essentially identical to the original Macintosh, it originally debuted in beige and was labeled Macintosh Plus on the front, but Macintosh Plus 1MB on the back to denote the 1MB RAM configuration with which it shipped. In January 1987 it transitioned to Apple's long-lived Platinum gray color with the rest of the Apple product line. In January 1988 with reduced RAM prices, Apple began shipping 2 & 4MB configurations and re-branded it simply Macintosh Plus. Among other design changes, it included the same trademarked inlaid Apple logo and recessed port icons as the Apple IIc and IIGS before it, but it essentially retained the original design.
An upgrade kit was offered for the earlier Macintosh 128K and Macintosh 512K/enhanced, which included a new motherboard, floppy disk drive and rear case. The owner retained the front case, monitor, and analog board. Because of this, there is no "Macintosh Plus" on the front, and the Apple logo is recessed and in the bottom left hand corner. However, the label on the back of the case reads "Macintosh Plus 1MB". The new extended Plus keyboard could also be purchased. Unfortunately, this upgrade cost almost as much as a new machine.
The Mac Plus itself could be upgrade further with the use of third party accelerators, which clipped onto the 68000 processor, allowing the Plus to run up to a 32MHz 68030 processor and adding up to 16MB RAM. allowing it to run Mac OS 7.6.1.
From the debut of the Macintosh 128K through the Macintosh Plus, various third-party cooling add-ons were available to help increase airflow through the unit (including the fanless Mac Chimney which cooled by convection). Apple finally reorganized the Compact Macintosh case to accommodate a fan with the release of the Macintosh SE. Another popular remedy was to create more vents so that more air could escape.