Xref: utzoo comp.sys.atari.st:37496 comp.sys.atari.st.tech:2089 Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!usc!elroy.jpl.nasa.gov!lll-winken!sun-barr!newstop!sun!imagen!atari!apratt From: apratt@atari.UUCP (Allan Pratt) Newsgroups: comp.sys.atari.st,comp.sys.atari.st.tech Subject: Re: Weird TT hard disk thingy Message-ID: <2910@atari.UUCP> Date: 23 Apr 91 20:33:20 GMT References: <1991Apr16.042133.20872@mailer.cc.fsu.edu> <1991Apr16.195300.1906@jato.jpl.nasa.gov> <1991Apr17.154845.29875@newcastle.ac.uk> Organization: Atari Corp., Sunnyvale CA Lines: 89 D.C.Halliday@newcastle.ac.uk (Dave Halliday) writes: >In article <1991Apr16.195300.1906@jato.jpl.nasa.gov>, >hyc@hanauma.jpl.nasa.gov (Howard Chu) writes: >|>In article <1991Apr16.042133.20872@mailer.cc.fsu.edu> >boyd@nu.cs.fsu.edu writes: >|>>My friend managed to get his external Supra HD connected to his TT >|>>(which has an internal SCSI device). The TT differentiates between >|>>SCSI and ASCI devices. The internal drive is set at SCSI 0, so my >|>>friend set his Supra at SCSI 1, so they would not confict. This >|>>turned out to be the problem. BOTH drives had to be set to SCSI 0 >|>>to work. Extremely weird. Anyone have an explination? >|> >|>What did he plug the Supra into, daisy chained off the SCSI port, or >|>the Atari DMA port? If DMA port, then the answer is that you're using two >|>separate buses... >Yes, but why does this explain why it will not work with an id other >than 0? I can see that if TT SCSI and ASCI are seperate buses then it is >ok to use the same id. Does this meen that the TT ASCI port only >supports one device not the full 8 on the ST. If it supports the full 8 >then with two buses or 16 SCSI devices the TT can handle some serious >backing storage :-> [I posted this earlier, but from the look of it the message didn't leave my site.] It's not the least bit wierd if you work through the logic of the busses. The fatal flaw in your reasoning is that you think since both drives are SCSI drives, they should have different SCSI unit numbers. What's actually happening as far as the TT is concerned is that you have one SCSI drive and one ACSI drive. The Supra drive is connected through a controller which lets you plug the SCSI drive into the ACSI bus. The controller, in essence, creates a tiny SCSI bus between it and the drive you connect to it. This controller will only control one unit, and it has to be SCSI unit 0. The controller probably has a switch of its own, to tell it which ACSI drive it should respond as. This is a SCSI bus | ---------- | | TT | | | | v ------------------------------------ | SCSI --X<---->| Internal SCSI drive, SCSI unit 0 | | BUS | ------------------------------------ | | | | -------------------- ------------------ | ACSI --X<---->| Supra Controller |<---->| External drive | | BUS | ^ | ACSI unit 0 | ^ | SCSI unit 0 | | | | | ACSI <--> SCSI | | ------------------ ---------- | -------------------- | | | This is an ACSI bus This is a SCSI bus If you add another Supra controller (or ICD controller or any SCSI-to-ACSI converter) to the ACSI bus, you would have to make it ACSI unit 1, but the drive it controls would still be SCSI unit 0, and there's no conflict because it's the only SCSI drive on the SCSI bus that the controller creates between itself and that drive. Get the picture? More minutae: HDX asks "SCSI or ACSI" when you select a drive; it's talking about SCSI or ACSI as the TT sees things, not necessarily which kind of mechanism it is. Almost all Atari drives are now SCSI drives with an ACSI-to-SCSI converter inside the case, where you don't see it. The Megafile 44 is a good example. Some used to be (and may still be) ST-506 drives with an ST506-to-ACSI converter inside the case, so don't count on one or the other without checking. The chief difference between SCSI and ACSI in the TT is that the SCSI bus supports the full SCSI command set, and ACSI doesn't. One important command which ACSI does not support is "inquire capacity." When you can do "inquire capacity" you don't need to know anything else about the drive to format or partition it, ergo no wincap and no "click on the drive type" box. Wincap is still required for HDX to be able to format and partition some (all?) ACSI drives. A final note: Mega STe's have an internal SCSI drive like TT's, but again, there is a SCSI-to-ACSI converter inside the box, so as far as TOS and HDX are concerned, it's an ACSI drive. Mega STe's don't really have SCSI, even though it kind of looks like they do. ============================================ Opinions expressed above do not necessarily -- Allan Pratt, Atari Corp. reflect those of Atari Corp. or anyone else. ...ames!atari!apratt