This message is from the T13 list server.
On Wed, 29 Jan 2003 09:34:16 -0600, Elliott, Robert (Server Storage) wrote: >This message is from the T13 list server. > >The SCSI architecture model requires byte granularity for >data transfers by all SCSI transport protocols (see sam3r04 >section 5.4.3 - Data transfer protocol services). > >If ATAPI lacks this, it's an(other) area where it's not quite >SCSI compliant. Now we are back to one of the most basic questions regarding ATAPI: Is it SCSI or is it something else? The original definition of ATAPI was based on the idea that it was not really SCSI - it was something else that looked like SCSI on the surface but was less complex. (Sound familar? Look at SATA/SAS marketing hype.) T10 could resolve this problem by identifing ATAPI as one of the SCSI transports. But T10 has never done this. The only recognition given by T10 to ATAPI is some brief comments in the MMC-x documents. So I think we (T13) must say that ATAPI is "SCSI like". And when talking about parallel ATA/ATAPI we must say that the physical ATA interface is able to transfer only 2 bytes at a time. Therefore, all data transfers are an even number of bytes. An ATA/ATAPI host (application software or OS device driver) that attempts a data transfer for an odd number of bytes must be aware that the physical interface does not suppot this and this software must be prepared to recognize that there may be a pad byte at the end of the transfer. I don't see T13 doing anything to change the ATA/ATAPI parallel interface data transfer protocols. But what about SATA? Has this been addressed there? Or is ATAPI executed over SATA also just "SCSI-like"? Hale *** Hale Landis *** www.ata-atapi.com ***
