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Adaptec also developed generic SCSI disk and CD-ROM drivers for DOS (ASPICD.SYS and ASPIDISK.SYS). [3]: 60–61 At least a couple of other programming interfaces for SCSI device drivers competed with ASPI in the early 1990s, including CAM (Common Access Method), developed by Apple; and Layered Device Driver Architecture, developed by Microsoft.
At first, Adaptec focused on devices with Parallel SCSI interfaces. Popular host bus adapters included the 154x/15xx ISA family, the 2940 PCI family, and the 29160/-320 family. Their cross-platform ASPI was an early API for accessing and integrating non- disk devices like tape drives , scanners and optical disks .
On a parallel SCSI bus, a device (e.g. host adapter, disk drive) is identified by a "SCSI ID", which is a number in the range 0–7 on a narrow bus and in the range 0–15 on a wide bus. On earlier models a physical jumper or switch controls the SCSI ID of the initiator ( host adapter ).
USB Attached SCSI (UAS) or USB Attached SCSI Protocol (UASP) is a computer protocol used to move data to and from USB storage devices such as hard drives (HDDs), solid-state drives (SSDs), and thumb drives.
[6] [7] The drives are identified by the operating system as "IMG VP0" and "IMG VP1" respectively. Early external SCSI-based Zip drives were packaged with an included SCSI adapter known as Zip Zoom. The Zip Zoom is a relabeled ISA Adaptec SCSI host controller.
The storage port drivers provide an interface for Win32 applications to send SCSI Command Descriptor Block (CDB) messages to SCSI devices. The interfaces are IOCTL_SCSI_PASS_THROUGH and IOCTL_SCSI_PASS_THROUGH_DIRECT. Applications can build a pass-through request and send it to the device by using this IOCTL.
The range limitations of the data cable allows for external SCSI devices. Originally SCSI data cables used single ended (common mode) data transmission, but server class SCSI could use differential transmission, either low voltage differential (LVD) or high voltage differential (HVD). ("Low" and "High" voltages for differential SCSI are ...
For Wide SCSI-2, the most common connector was the larger 68-pin sibling of the HD50, known as the HD68, MiniD68, HPDB68, and sometimes as "SCSI-3". This is about 1 7/8” (47mm) wide. [3] IBM used the HDCN68 on some RS-6000 systems, and it seems likely that a few other manufacturers used other alternatives.