Editing Macintosh Plus (section)

== Memory and Storage ==

The Macintosh Plus shipped with significant memory improvements over its predecessors:

=== RAM Configuration ===
* '''Standard RAM''': 1 MB of RAM standard, expandable to 4 MB
* '''Memory Architecture''': The Mac Plus was the first Apple computer to utilize user-upgradable SIMM memory modules instead of single DIP DRAM chips
* '''SIMM Slots''': Four SIMM slots were provided and the computer shipped with four 256 KB SIMMs, for 1 MB total RAM
* '''Maximum Capacity''': By replacing them with 1 MB SIMMs, it was possible to have 4 MB of RAM

=== ROM and System Software ===
The Mac Plus has 128 KB of ROM on the motherboard, which is double the amount of ROM in previous Macs; the ROMs included software to support SCSI, the then-new 800 KB floppy drive, and the Hierarchical File System (HFS). The Plus went through two ROM revisions during its general market relevance. 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 POST.

=== Storage Systems ===
It has what was then a new 3+1⁄2-inch double-sided 800 KB floppy drive, offering double the capacity of floppy disks from previous Macs, along with backward compatibility. The drive is controlled by the same IWM chip as in previous models, implementing variable speed GCR.