Chapter OneIntroductionDocument ScopeThis manual provides information on installation and defines the program interfacesof the AHA-1740A/1742A/1744 intelligent host adapters in EISA bus-based systems.Programming peripheral drivers directly to the hardware interface of the board is notrecommended. The ASPI (Advanced SCSI Programming Interface) specifications pro-vide a simpler and more flexible interface which is protected against changes, up-grades and obsolescence of the boards.PurposeThe Adaptec AHA-1740A/1742A/1744 provides a powerful multitasking interface be-tween the Extended Industry Standard Architecture (EISA) bus and the Small Com-puter System Interface (SCSI) bus.The AHA-1740A/1742A/1744 is a high-performance intelligent host adapter whichsupports a maximum asynchronous SCSI rate of 2.0 MBytes/second and a synchro-nous transfer rate of 10.0 MBytes/second. It supports multithreaded I/O operations,allowing simultaneous operations on multiple targets/LUNs. Disconnect/Reconnectsupport maximizes bus utilization for multiple target systems. Target mode opera-tion allows the AHA-1740A/1742A/1744 to receive information from other host adapt-ers. Scatter/Gather allows high performance even in systems with fragmentedmemory buffers.The AHA-1740A/1742A/1744 provides a solution for system applications requiringvery high performance, configuration flexibility, multithreaded I/O capability, andsystem redundancy. The Adaptec BIOS also allows the AHA-1740A/1742A/1744 to beused in place of a standard hard disk controller.The AHA-1740A/1742A host adapter provides high-performance host adapter cir-cuitry connected to the more common single-ended SCSI bus. The SCSI specificationrecommended maximum cable length for 5 MBytes/second synchronous data transferis 6 Meters, or about 20 feet.The AHA-1744 host adapter provides identical host adapter circuitry, but connects toa differential SCSI bus. The SCSI specification recommended maximum cable lengthfor 5 MBytes/second synchronous data transfer is 25 Meters, or about 82 feet.1-1
