rrw@naucse.UUCP (Robert Wier) (01/26/89)
We are looking for information on how compatible are devices designed for SCSI, *really*? For example, could you buy a HD being marketed for the Macintosh, and use it on an HP workstation which has a SCSI port? I have heard (I can't remember where exactly), that Apple's use of the SCSI is somewhat non-conforming to the standard. Is this true? How about other devices? Is everyone else compatible? Any comments would be greatly appreciated. Feel free to respond by E-Mail if you wish not to post comments here, and I will summarize. Many thanks- -Bob Wier at Flagstaff, Arizona Northern Arizona University ...arizona!naucse!rrw | BITNET: WIER@NAUVAX | *usual disclaimers*
rrw@naucse.UUCP (Robert Wier) (01/26/89)
In my request for information on SCSI "standard" devices, I have found such a discussion already going on under comp.arch, with the most recent message being numbered here as #7960, "Decstation 3100 info". I would be interested in any other comments in addition, though. thanks -Bob Wier at Flagstaff, Arizona Northern Arizona University ...arizona!naucse!rrw | BITNET: WIER@NAUVAX | *usual disclaimers*
billkatt@sol.engin.umich.edu (Steve Bollinger) (01/26/89)
In article <1138@naucse.UUCP> rrw@naucse.UUCP (Robert Wier) writes: > > We are looking for information on how compatible are devices designed > for SCSI, *really*? For example, could you buy a HD being marketed > for the Macintosh, and use it on an HP workstation which has a > SCSI port? I have heard (I can't remember where exactly), that > Apple's use of the SCSI is somewhat non-conforming to the standard. > Is this true? How about other devices? Is everyone else compatible? There are really two ways in which the mac is non-standard. First, they only use a 25-pin connector. This is not an issue because the 25 pins they omitted are all grounds, and most SCSI cables just split the ground which is available out to 26 different lines. There is no standard connector for SCSI, Apple uses a centronics type (except on the back of the Plus, SE, and I series), and Sun uses a D-shell connector. The other way that Apple is non-standard is that it requires a driver for its SCSI drives. This is good because that way both standard and non-standard drives can be supported, however, I would rather that they used direct SCSI calls and required standard drives. The important factor is that with the correct cable and driver, you can use any standard (and many non-standard) SCSI drive on a Mac. On the other hand, we have a Maxtor drive which works on a Mac but not a Sun. I repeat: any drive which works on a NeXT or a Sun will work on a Mac, so stop yer gripin' B-) +----------------------+----------------------------------------------------+ | Steve Bollinger | Internet: billkatt@caen.engin.umich.edu | | 4297 Sulgrave Dr. +------+---------------------------------------------+ | Swartz Creek, Mi. 48473 | "My employer doesn't take my opinion any | +-----------------------------+ more seriously than you do." | | "You remember the IIe, it +---------------------------------------------+ | was the machine Apple made before they decided people didn't need | | machines with big screens, color, or slots." | | - Harry Anderson (from NBC's Night Court) | +---------------------------------------------------------------------------+
rjn@hpfcdc.HP.COM (Bob Niland) (01/26/89)
re: "For example, could you buy a HD being marketed for the Macintosh, and
use it on an HP workstation which has a SCSI port?"
We currently estimate that any random third-party SCSI disk has about a 50%
chance of working with the HP9000 Series 300 boot ROM (rev C or later) and
the HP-UX disk driver (rev 6.0 or later).
If the incompatibility is restricted to software, the answer is yes in any
case. Since if it doesn't work, you can make it work. We ship the scsi.c
driver source with HP-UX. Hack away!
> I have heard (I can't remember where exactly), that > Apple's use of the
> SCSI is somewhat non-conforming to the standard.
The MAC computers use a 25-pin DB25 (RS-232C style) connector instead of
the standard ALT-2 50-pin, but other than that, I am not certain of how
they vary from ANSI. I'll ask our SCSI guru to respond.
Bob Niland ARPA:rjn%hpfcrjn@hplabs.HP.COM UUCP:[hpfcse|hplabs]!hpfcla!rjnkinsell@hpfclm.HP.COM (Dave Kinsell) (01/27/89)
>> I have heard (I can't remember where exactly), that > Apple's use of the >> SCSI is somewhat non-conforming to the standard. >The MAC computers use a 25-pin DB25 (RS-232C style) connector instead of >the standard ALT-2 50-pin, but other than that, I am not certain of how >they vary from ANSI. Mac uses a DB25 at the computer, but sometimes adapter cables are used to convert to Alternative 2 connectors at the peripheral. Some of the ground wires are sacrificed in this scheme. Alt 2 connectors are what some people call Centronics style, but with 50 pins. AMP calls them "Champ" and Amphenol calls them "Microribbon". I've seen discs sold for Mac that use DB25, and others that use Alt 2 connectors. External peripherals sold for SUNs typically use DB50 connectors. I don't know if that was an attempt to lock out competition with non-standard connectors, or if they predated development of the Alt 2 recommendation in Appendix D of the SCSI standard. The Mac approach was most likely used to save back panel space. -Dave Kinsell kinsell@hpfclm.HP.COM
jlohmeye@entec.Wichita.NCR.COM (John Lohmeyer) (01/28/89)
In article <5340003@hpfcdc.HP.COM> rjn@hpfcdc.HP.COM (Bob Niland) writes: >The MAC computers use a 25-pin DB25 (RS-232C style) connector instead of >the standard ALT-2 50-pin, but other than that, I am not certain of how >they vary from ANSI. I'll ask our SCSI guru to respond. While the MAC does have a DB25 on the MAC, it uses miniature ribbon connectors (SCSI standard) on the peripheral boxes. There are several ways that the MAC deviates from "typical" SCSI (I didn't say "standard"). A few that I can think of off the top of my head are: 1. It doesn't terminate the bus at the MAC end of the cable. 2. It doesn't handshake bytes properly (this may have been fixed). 3. It won't boot from a SCSI disk that reports unit attention after power-up (required by the SCSI standard). (Actually, all of the above are violations of the SCSI standard.) In addition to these problems, Apple didn't go out of its way to make it easy to add on third-party SCSI devices. (Nor did they really try to block add ons.) Apple recognizes that they have some problems and somewhere I have a copy of an Apple application note that details what the problems are and how to work around them. I think they are making a real effort to improve the situation. John Lohmeyer, NCR Corp. j.lohmeyer@Wichita.NCR.COM
ts@cup.portal.com (Tim W Smith) (01/31/89)
There most certainly is a standard SCSI connector. Many boring pages of the ANSI SCSI standard are devoted to describing in excruciating detail what standard SCSI connectors look like. Tim Smith ps: the main problem that one is likely to encounter trying to use a standard SCSI drive on the Mac is the various bugs in the Mac plus ROM. Here are some of the problems that can cause serious trouble: 1. ROM SCSI Manager can't read more than one block at a time safely. 2. Blind transfers can't be used safely. 3. Original plus ROM can't deal with drives that do UNIT ATTENTION on reset. Problems 1 and 2 can be worked around in software ( simply don't do blind or multiblock transfers until the SCSI Manager patches are loaded ). Problem 3 is more of a problem. Either get the later plus ROMs, or convince your drive not to do UNIT ATTENTION ( many have such on option ).
kaufman@polya.Stanford.EDU (Marc T. Kaufman) (02/01/89)
In article <317@entec.Wichita.NCR.COM> jlohmeye@entec.UUCP (John Lohmeyer) writes: >There are several ways that the MAC deviates from "typical" SCSI (I didn't >say "standard"). A few that I can think of off the top of my head are: - 1. It doesn't terminate the bus at the MAC end of the cable. If the MAC has an internal disk, the bus is terminated at the disk, which is one end of the cable. - 2. It doesn't handshake bytes properly (this may have been fixed). Fixed in later (+, II) hardware. However the software does not handle abnormal terminations of "blind" read/write properly, and may lose the last character if the count doesn't match. - 3. It won't boot from a SCSI disk that reports unit attention after - power-up (required by the SCSI standard). Neither will it boot from a disk that doesn't have an Apple driver on it. This is a software problem, though, and should be fixable. >(Actually, all of the above are violations of the SCSI standard.) In addition >to these problems, Apple didn't go out of its way to make it easy to add on >third-party SCSI devices. (Nor did they really try to block add ons.) True on both counts. I have added an output-only device... but I had to implement a "Read" instruction that returned with no-error in order for the Mac to boot with the device on the bus. Marc Kaufman (kaufman@polya.stanford.edu)