Blind transfers refer to the way data is transferred to the hard drive by the driver. In drive formatting software that supports turning this option on or off, a different version of the driver is written to the driver partition.
If blind transfers are not enabled, polled transfers are used. Polled transfers are used with slow SCSI devices or SCSI devices attached to older Macintosh computers. Older, in this case, means the Macintosh SE and Macintosh Plus. In polled transfer mode, the SCSI Manager polls the SCSI controller to see if there is data to be read before reading or that the last set of data was written before sending the next set. This is the safest method for performing reads and writes.
When using blind transfers, SCSI Manager assumes the data can be written to or read from the drive as fast as SCSI Manager can read it. If a slow drive is used, there is the potential for data corruption due to timing problems. If the drive cannot write the data fast enough, data will be lost due to overflow of data buffers. If the drive cannot supply data fast enough during a read, SCSI Manager will be reading erroneous information out of the controller because the data has not arrived yet. Blind transfers can significantly improve the speed of SCSI throughput.
Apple HD SC Setup determines whether or not to install the driver which uses blind transfers based on the computer the drive is attached to when it is formatted. Apple HD SC Setup only turns off blind transfers on drives formatted while connected to the Macintosh SE or Macintosh Plus.
Article Change History:
09 Nov 1995 - Corrected minor typo.
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