The Macintosh Plus computer is 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.