rr@pika.mips.com (Robert "Bob" Rodriguez) (11/16/89)
Can anybody comment on whether SCSI-2 is dead and disk manufacturers are going yo jump to something called SCSI-3. I have heard rumors..... AdThanksvance.... Robert Rodriguez +------+ _____ ___ -- @ rr@mips.com | /// | |\ /| | | | |__` One of the Fathers |/// | | \/ | | |--' \ of PMAX |//____| | | __|__ | \__/
jlohmeye@entec.Wichita.NCR.COM (John Lohmeyer) (11/17/89)
In article <31465@mips.mips.COM> rr@pika.mips.com (Robert "Bob" Rodriguez) writes: >Can anybody comment on whether SCSI-2 is dead and disk manufacturers >are going yo jump to something called SCSI-3. I have heard rumors..... > As with most rumors, this one is more wrong than right. The disk manufacturers are working on implementing SCSI-2, but there is some confusion over the cables. The cable issue probably fueled this rumor. SASI and SCSI-1 defined a single 50-conductor cable which transfers 8-bit data. The other signals are used for control, grounds, etc. SCSI-2 defined an optional second cable to allow another 8 or 24 bits of data to achieve a total of 16 or 32 bits. This option is referred to as wide SCSI. The new cable is called the B cable and the original cable (same as SCSI-1) is called the A Cable. The B Cable uses 68-conductors when fully populated for 32-bits. It uses 68-pin connectors even when used for 16-bits. After SCSI-2 was forwarded out of X3T9.2 (the committee that developed it), a proposal for doing 16-bit data transfers with only one 68-conductor cable was received. This cable has become known as the P Cable. (I'm not sure why George Penokie called it the P Cable -- one can only guess :-) Of course, the disk manufacturers are much more interested in doing 16-bit devices with one cable than with 2 cables. Especially since the committee has found a clever way of permitting compatibility with 8-bit devices: The middle conductors of the P Cable are the same as in the SCSI-1/SCSI-2 A Cable. I won't bore you with further talk about the Q Cable (P+Q= 32 bits) or the S Cable (32-bits, with a centered P Cable), but suffice it to say that the committee has plenty of ideas! :-) All this gets even more complicated because the committee still has not come to grips with the scope of the SCSI-3 project and because SCSI-2 is not beyond change. As chairman of the SCSI committee, I have received a public review comment from Western Digital saying we should remove the B Cable from SCSI-2 and consider adding the P Cable. I understand that Micropolis plans to submit a similar public review comment just requesting that the P Cable be added as an appendix to SCSI-2. (This means it is not mandatory, but then wide SCSI isn't either.) The committee will address these comments at our Dec. 4-5 meeting. It should be real fun ;-). In any case, wide SCSI is only part of SCSI-2 -- but a tangible part. I believe the disk manufacturers will use the P Cable approach, but otherwise follow SCSI-2 PROVIDED they need 16-bit data transfers. If you only need 8-bit data, then the A Cable is fine... -- John Lohmeyer J.Lohmeyer@Wichita.NCR.COM NCR Corp. uunet!ncrlnk!ncrwic!entec!jlohmeye 3718 N. Rock Rd. Voice: 316-636-8703 Wichita, KS 67226 SCSI BBS 316-636-8700 300/1200/2400 24 hours