Hard Disk SC

An Apple Hard Disk 20SC

The Hard Disk SC is a line of Apple hard drives released in 1986 that includes the first Apple HDD to contain SCSI compatibility. Multiple computers of the classic Macintosh could be connected to the SC models, including the Macintosh Plus, SE, SE/30, II, IIcx, and IIx. It was also possible to connect an Apple IIe and IIgs to an SC drive via the Apple II SCSI Interface Card.

Technical specifications

The SC was a considerable improvement over its predecessors, the original Hard Disk 20 and the Apple ProFile, as it could transfer files over 1 megabyte, although this varied due to how SCSI was implemented in various computers. Storage capacities varied between SC models, with the 20SC, 40SC, 80SC, and 160SC reaching a maximum of 20, 40, 80, and 160 megabytes respectively.

SCSI terminators were necessary in the case of two or more peripherals connected to an SC via daisy-chaining an Apple II SCSI Card. There had to be only two terminators at the beginning and end of the connection; failing to do so could result in damage to all SCSI devices connected. A terminator helps in removing unwanted signals from resulting data, meaning SCSI data transfer is faster.

Each SC model contained a 3.5" hard drive, with the case itself being able to accommodate up to 5.25 inch tall mechanism. The SC models also have two 50-pin SCSI connectors; one connected the unit to a computer, while the other allowed the seven other possible peripherals to connect to the SC.