The Dawicontrol Scsi Software Concept; Synchronous And Asynchronous Data Transmission - Dawicontrol DC-29160 U3W Mode D'emploi

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5. The Dawicontrol SCSI Software Concept

As SCSI devices are generally neither supported directly by the PC BIOS nor by
the operating system, their operation requires additional software which is supplied
partly by the SCSI host adapter BIOS and partly by the various device drivers.
Basically, two types of SCSI device installation can be distinguished: installation
by the host adapter BIOS and installation by a device driver.
Installation by the SCSI BIOS is particularly suited for hard disks. It's true that disk
cartridges can be operated as BIOS hard disks, but you have to be extremely careful
in this respect. As hard disks normally can not be exchanged when in operation, the
BIOS interface does not offer the possibility to inform the respective operating system
of the exchange of the medium. Consequently, the possibility of a hard disk suddenly
displaying a completely different data structure is not taken into account either. If you
should nevertheless opt for operating a disk cartridge as a BIOS compatible hard disk,
it is advisable to restart your computer in case of a medium change.
The driver-based installation of SCSI devices, on the other hand, offers no such
restrictions. Up to now however, the lack of a uniform software standard has been a
problem. It was necessary, for instance, for the drivers of the various device types to
be specifically adapted to the hardware of the respective host adapter. That is why
manufacturers of back-up software, for instance, did not have the possibility to support
all the current host adapters. In the meantime however, two standards have asserted
themselves: the ASPI (advanced SCSI programming interface) interface developed
by the Adaptec company, and the CAM (common access method) interface defined
by an independent committee. In both cases, the device drivers are no longer based
on the hardware of the host adapter, but on the respective software interface supplied
by the SCSI host adapter.
The Dawicontrol SCSI host adapter offers both standard SCSI interfaces (CAM
and ASPI) and enables the simultaneous use of device drivers based on CAM and
ASPI. This assures them maximum flexibility and security for the future. For instance,
the device drivers of various other manufacturers can be operated with the Dawicontrol
SCSI host adapter, too.

5.1. Synchronous and Asynchronous Data Transmission

The SCSI interface supports two different kinds of data transmission: synchronous
and asynchronous data transmission. All SCSI devices select asynchronous data
transmission as the standard setting after they have been switched on. The faster
synchronous data transmission of 160 MB / s is only activated when the SCSI host
adapter and the respective SCSI device have convened on synchronous data
transmission by message transfer, thus determining the data transmission rate and
checking transfer security via domain validation.
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