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$2,599. 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. Originally, the computer's case was the same beige color as the original Macintosh, Pantone 453; however, 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 Software 5, System 6, and System 7, up to System 7.5.5, but not System 7.5.2.