Path: utzoo!utgpu!news-server.csri.toronto.edu!mailrus!umich!samsung!uunet!mcsun!hp4nl!fwi.uva.nl!dolf From: dolf@fwi.uva.nl (Dolf Starreveld) Newsgroups: comp.sys.mac.hardware Subject: Re: Follow up to hard disk autoparking and a SCSI question... Message-ID: <1042@carol.fwi.uva.nl> Date: 31 May 90 17:37:10 GMT References: <1990May31.051839.23825@athena.mit.edu> Sender: news@fwi.uva.nl Lines: 73 shahn@hstbme.mit.edu (Samuel Hahn) writes: >1) A posted a question a few days ago asking if APPLE hard disks had their >heads automatically parked on shut down by the system software. I received two >conflicting answers. One person said yes, System 6.0.4 and later sends a >head parking command to the hard disk. Another said no, no such command is sent >because if it were, all hard disks would be autoparked. In my opinion these two >views are not necessarily conflicting. My original question was if APPLE hard >disks (or those formatted with Apple's HD Setup) are parked. Just because 3rd >party drives aren't parked, doesn't mean Apple's couldn't be. >Can anyone from Apple confirm/deny my suspicions? I am not from Apple, but ... Whether heads are automatically parked depends on the drive intercepting the shutdown using the start manager. Once this is implemened, the driver might actually send a Stop Unit command to "park". I don't know whether or not Apple driver software does this, but I think it doesn't. In any case, whatever driver software, if the driver can't know whether the system is shut down it can't autopark anyway. This is the case with older system versions that do not implement the start manager. It is definitely not true that a single command could park all hard disks at once, simply because every scsi command must contain a target id (0-6) and there is not ID that functions as a "broadcast" id. Therefore a single command can not do this to all disks! It also is not true that 3rd party hard disks are not parked. Again, it depends on the software. A friend and I have implemented a wide range of SCSI drivers. In general, all mechanism park automatically when powered down. Thus, in general, the parking is never needed and we don't implement it. We do implement it, however, on SyQuest and other removable media drives, for instance on the Sony 650Mb optical mechanisms. The reason is that we allow removal of the media whenever no partitions from that media are mounted. The Stop Unit command stops the spindle motor and retreats the heads. Subsequently a Release Media command is used to actually allow you to remove the media. On the Sony we do this slightly different on shutdown. In that case we not only release, but also initiate cartridge eject. >2) SCSI termination: There has been a lot of talk lately about internal vs. >external termination for external hard disks (most notably SyQuests). My >current set up is a Mac II w/ 40 meg INTERNAL HD and a LW II SC (properly >termianted of course!). >Now if I wanted to add an external SyQuest, does it matter if it is internally >or externally terminated? My IISC is externally terminted so if the SyQuest >is internally terminated, can I just make it the end of my SCSI chain and >take the terminator off of the IISC? AND if I can do that, will things still >work properly, i.e. can I use my printer without having to turn on my SyQuest >and vice versa? Yes, it does matter. First of all, you already have two terminators at both ends of the SCSI chain (internal + printer). If you intend to place the SyQuest somewhere external, but before the LaserWriter, the Syquest should not have any termination! If you want to locate it beyond the printer, the SyQuest should be terminated and not the printer. Note: SyQuest mechanisms are particularly sensitive to improper termination and this will usually show by incorrect functioning. In general there is no difference between internal and external termination, provided it is done correctly. This means a number of things, but the most important to remember is that each terminator pack need power to function. This may either come from the device itself (usually only when the device is stiched on), or from the bus itself (this requires something newer than a MacPlus since that does not put terminator power on the bus. Some devices allow a mix. Internal power when switched on, external when device switched off. Note: If you depend on terminator power through the bus, each and every device must connect the terminator power line from in to out connector, or it won't work! --dolf -- Dolf Starreveld Phone: +31 20 592 5056/5022 (FAX: 5155), TELEX: 10262 HEF NL EMAIL: dolf@fwi.uva.nl (dolf%fwi.uva.nl@hp4nl.nluug.nl) SNAIL: Dept. of Math. and Computing Science, University of Amsterdam, Kruislaan 409, NL-1098 SJ Amsterdam, The Netherlands