|Release date||January 16, 1986|
|Discontinued||October 15, 1990|
|Operating system||3.0–6.0.8, 7.0-7.5.5|
|CPU||Motorola 68000 @ 8 MHz|
|Memory||1 MB, expandable to 4 MB (150 ns 30-pin SIMM)|
The Macintosh Plus computer was the third model in the Macintosh line, introduced on January 16, 1986, two years after the original Macintosh and a little more than a year after the Macintosh 512K, with a price tag of US$2599. As an evolutionary improvement over the 512K, it shipped with 1 MB of RAM standard, expandable to 4 MB, and an external SCSI peripheral bus, among smaller improvements. It originally had the same generally beige-colored case as the original Macintosh ("Pantone 453"), but in 1987, the case color was changed to the long-lived, warm gray "Platinum" color. It is the earliest Macintosh model able to run System 7 OS.
Introduced as the Macintosh Plus, it was the first Macintosh model to include a SCSI port, which launched the popularity of external SCSI devices for Macs, including hard disks, tape drives, CD-ROM drives, printers, and even monitors. The SCSI implementation of the Plus was engineered shortly before the initial SCSI spec was finalized and, as such, is not 100% SCSI-compliant. SCSI ports remained standard equipment for all Macs until the introduction of the iMac in 1998, which replaced most of Apple's legacy ports with USB.
The Macintosh Plus was the last classic Mac to have a phone cord-like port on the front of the unit for the keyboard, as well as the DE-9 connector for the mouse; models released after the Macintosh Plus would use ADB ports.
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. Like the 400 KB drive before it, a companion Macintosh 800K External Drive was an available option. However, with the increased storage capacity combined with 2-4x the available RAM, the external drive was less of a necessity than it had been with the 128K and 512K.
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 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 nine 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 512×342 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. Microsoft Excel and PowerPoint (originally by Forethought) were actually developed and released first for the Macintosh, and similarly Microsoft Word 1 for Macintosh was the first time a GUI version of that software was introduced on any personal computer platform. For a time, the exclusive availability of Excel and PageMaker on the Macintosh were noticeable drivers of sales for the platform.
The case design was 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, and the keyboard's keycaps changed from brown to gray. In January 1988, with reduced RAM prices, Apple began shipping 2 and 4 MB 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 of upgraded units, and the Apple logo is recessed and in the bottom left hand corner of the front case. 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 upgraded further with the use of third-party accelerators. When these were clipped or soldered onto the 68000 processor, a 32 MHz 68030 processor could be used, and up to 16 MB RAM. This allowed it to run Mac OS 7.6.1.
At present, there is a program called Mini vMac that can emulate a Mac Plus on a variety of platforms, including Unix, Windows, DOS, Mac OS, Mac OS X, Pocket PC, iOS (on jailbroken devices) and even Nintendo DS.
Long production life 
Although the Mac Plus became overshadowed by two new Macs in March 1987, (the Macintosh SE and the Macintosh II), it remained in production as a cheaper alternative until the introduction of the Macintosh Classic on 15 October 1990. This makes the Macintosh Plus the longest-produced Macintosh ever. It continued to be supported by versions of the Mac OS up to version 7.5.5, released in 1996. Additionally, during its lifespan, it was heavily discounted like the 512K/512Ke before it and offered to the educational market badged as the "Macintosh Plus ED". Due to its popularity, long life and its introduction of many features that would become mainstays of the Macintosh platform for years, the Plus was a common "base model" for many software and hardware products.
The lack of fan could cause the life of a Macintosh Plus to end early for some users. As the power supply would heat up, solder joints inside it would fracture causing many problems, such as loss of deflection in the monitor or a complete loss of power. As in most early compact Macs, the problem was common in the yoke connector, flyback transformer, and horizontal drive coupling capacitor.
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. Apple finally reorganized the compact Macintosh case to accommodate a fan with the release of the Macintosh SE.
ROM revisions 
The Plus went through two ROM revisions during its life. The initial ROM was replaced after the first two months as it had a serious bug which prevented the Mac from booting if an external SCSI device was powered off. The second revision fixed a problem with some SCSI devices that could send the Mac into an endless reset at startup.
Timeline of compact Macintosh models
See also 
- History of computer design: Apple Macintosh
- History of computer design: Macintosh Plus
- Macintosh Plus Profile
- Technical Note HW11: Macintosh Plus ROM Versions
- Technical Note DV14: SCSI Bugs
| group2 = Peripherals
| list2 =
| group1 = Displays | list1 =
- Monitor III
- Monitor II
- AppleColor Composite IIe
- AppleColor High-Resolution RGB
- Macintosh Color
- AudioVision 14
- Multiple Scan 14
- ColorSync 750
| group2 = External drives| list2 =
| group3 = Input devices | list3 =
| group4 = Networking | list4 =
| group5 = Printers | list5 =
- Scribe Printer
- Dot Matrix Printer
- Letter Quality Printer
- 410 Color Plotter
- Color LaserWriter
| group7 = Newton | list7 =
| group8 = Other | list8 =
| below = Apple hardware since 1998 }}