pgn@osupyr.mast.ohio-state.edu (Paul G. Nevai) (09/17/88)
This is about SCSI's and Terminators!!! Oh boy, I thought I knew everyting about them, but when I opened (the first time in my life) the little booklet "Apple SCSI Cable System" which comes with the SCSI cable it turned out that I was DEAD wrong. (In what follows, all Hard Disks are assumed to be non-terminated, System Cables are DB 25 on one end and Centronics 50 on the other, Cable Extenders have Centronics 50 (M-F) on both ends.) For starters, did you know for instance, that Mac -- System Cable -- Hard Disk -- Teminator is wrong? The right configuration is Mac -- System Cable -- Teminator -- Hard Disk OK? Now, for advanced intermediates, did you know that Mac -- System Cable -- Cable Extender -- Teminator -- Hard Disk is wrong? The right configuration is Mac -- System Cable -- Terminator -- Cable Extender -- Teminator -- -- Hard Disk OK? (See page 7, fig. 5 in quoted booklet.) Isn't this surprising? Now, for pros, do you know where the terminator goes in Mac -- System Cable -- Cable Extender -- Hard Disk -- Cable Extender -- -- System Cable -- Hard Disk ? (In case you wonder how I can have this configuration of cables, that is DB 25 away from the Mac, then I tell you that my last Hard Disk has two DB 25 outlets) Is it Mac -- System Cable -- Teminator -- Cable Extender -- Hard Disk -- -- Cable Extender -- System Cable -- Teminator -- Hard Disk or Mac -- System Cable -- Cable Extender -- Teminator -- Hard Disk -- -- Cable Extender -- System Cable --Teminator -- Hard Disk or what else? For pros, here is another toughie: if the Hard Disk has two DB 25 outlets, then is it all right to use any DB-25 cable to connect it with the Mac, or are there special DB 25 SCSI cables? One more questions: why are ... -- Teminator -- Hard Disk (The End) and ... -- Hard Disk -- Teminator (The End) different? I am anxiously looking forward for prompt replies from The Experts i. e. the APPLE, SuperMac, CMS etc. guys!!! Sincerely, Paul Nevai pgn@osupyr.mast.ohio-state.edu Department of Mathematics TS1171@OHSTVMA.bitnet The Ohio State University 73057,172.Compu$erve 231 West Eighteenth Avenue 1-614-292-5310.office Columbus, OH 43210, U.S.A. 1-614-292-4975.dept P.S. Though one can have up to 20 feet of SCSI cable in a system, do not ever dare to test the limits or else you will have spectacular crashes. Trust me.
olson@endor.harvard.edu (Eric K. Olson) (09/19/88)
In a recent article Paul G. Nevai writes: >For starters, did you know for instance, that > Mac -- System Cable -- Hard Disk -- Teminator >is wrong? The right configuration is > Mac -- System Cable -- Teminator -- Hard Disk I've never found any difference between these two configurations. Some hard disks only have one plug, and you have to use the second configuration. >OK? Now, for advanced intermediates, did you know that > Mac -- System Cable -- Cable Extender -- Teminator -- Hard Disk >is wrong? The right configuration is > Mac -- System Cable -- Terminator -- Cable Extender -- Teminator -- > -- Hard Disk In fact, the first terminator should be right after the Mac, but it's not possible to put one there unless you put a terminated hard disk inside (like a Mac II or SE). The bus is long enough to want a terminator at BOTH ends (any long SCSI bus should have a terminator at both ends), but with Apple's cabling you can't plug a terminator right on the computer (because they use a DB25 connector instead of the standard). >Now, for pros, do you know where the terminator goes in > Mac -- System Cable -- Cable Extender -- Hard Disk -- Cable Extender -- > -- System Cable -- Hard Disk ? Use two, at the farthest ends of the bus you can get to: Mac - SystemCable - Term - Extender - HD - Extender - SystemCable - HD - Term >One more questions: why are > ... -- Teminator -- Hard Disk (The End) > ... -- Hard Disk -- Teminator (The End) >different? They aren't. Have you ever had one configuration work and the other fail? >P.S. Though one can have up to 20 feet of SCSI cable in a system, do not >ever dare to test the limits or else you will have spectacular crashes. >Trust me. I run about 10 feet of SCSI cable in my system without problems, but I wouldn't make it much longer and expect it to work right. Lexington Software Design: Tomorrow's Software Yesterday Eric K. Olson olson@endor.harvard.edu harvard!endor!olson D0760 (Name) (ArpaNet) (UseNet) (AppleLink)