Adaptec 1742A User Manual

Contents

BIOS Operation ModesThe AHA-1740A/1742A/1744 has two modes of operation: stand-ard mode and enhanced mode. The standard mode is softwarecompatible with the AHA-1540 series host adapter drivers. Theenhanced mode uses an advanced, high performance mailboxinterface and features full EISA 32-bit addressing. TheAHA-1740A/1742A/1744, in enhanced mode, can support upto 4 Gigabytes of host RAM memory. The two modes of theAHA-1740A/1742A/1744 are selected by running the EISA Con-figuration utility provided with every EISA machine. In general,the enhanced mode of the AHA-1740A/1742A/1744 should beused, whenever possible, for maximum performance.The two operation modes are described in the table below.Standard Mode(ISA compatible mode)Enhanced Mode(enhanced mailbox interface)32-bit host transfers at 33 MBytes/sec. 32-bit host transfers at 33 MBytes/sec.Addresses up to 16 MBytes host RAM. Addresses up to 4 Gigabytes host RAM.AHA-1540 series mailbox structure(compatible with AHA-1540 software).New high performance mailboxstructure.Supports Fast SCSI devices up to5 MBytes/sec.Supports Fast SCSI devices up to10 MBytes/sec.Boot only from SCSI ID 0. Boot from any SCSI ID.Drives spin up only at power-on. Drives spin up at power-on, or fromSCSI Start Unit command.Disconnect/reconnect, parity checking,and synchronous negotiation enable ordisabled for all SCSI targets.These parameters can be enabled ordisabled on a per target basis.Up to four host adapters can be in-stalled in the system.Up to twelve host adapters can beinstalled in the system.BIOS support for drives up to 1 Gi-gabyte in capacity under MS-DOS.BIOS support for drives up to 8Gigabytes in capacity under MS-DOS5.0 or higher.BIOS support for a maximum of 2SCSI drives.BIOS support for up to 7 SCSI drives(using MS-DOS 5.0 or higher).Table 1-2. AHA 1740A/1742A/1744 Operation ModesEISA-to-Fast SCSI Host Adapter Overview1-5