tedj@hpcilzb.HP.COM (Ted Johnson) (01/05/89)
I've always wondered how the Finder tells the difference between two diskettes which have the same name. I assume there is some sort of unique number associated with each diskette when it is initialized. Does anyone know the real story? -Ted
ephraim@think.COM (Ephraim Vishniac) (01/06/89)
In article <730076@hpcilzb.HP.COM> tedj@hpcilzb.HP.COM (Ted Johnson) writes: >I've always wondered how the Finder tells the difference between two >diskettes which have the same name. I assume there is some sort of >unique number associated with each diskette when it is initialized. >Does anyone know the real story? Logically, the information has to be somewhere in the volume information (the stuff in block 2). The only distinguishing fields I see are drCrDate (initialization time), drLsBkUp (last modification time), and the volume name. My experience is that if you eject a floppy, modify it on another machine, and re-insert it, it's considered to be a different floppy. So, the system certainly uses drLsBkUp and probably drCrDate as well. Reference: IM IV-161-166. Ephraim Vishniac ephraim@think.com Thinking Machines Corporation / 245 First Street / Cambridge, MA 02142-1214 "He shook his head to clear a momentary system error."
blob@Apple.COM (Brian Bechtel) (01/06/89)
In article <35187@think.UUCP> ephraim@think.com (Ephraim Vishniac) writes: >In article <730076@hpcilzb.HP.COM> tedj@hpcilzb.HP.COM (Ted Johnson) writes: > >>I've always wondered how the Finder tells the difference between two >>diskettes which have the same name. I assume there is some sort of >>unique number associated with each diskette when it is initialized. > >>Does anyone know the real story? > >Logically, the information has to be somewhere in the volume >information (the stuff in block 2). The only distinguishing fields I >see are drCrDate (initialization time), drLsBkUp (last modification >time), and the volume name. The sequence I see in the ROM listings is: check the signature word in the VCB check the creation date in the VCB check the volume name. if they match loop through any open files on the possibly remounted volume and see if they are still of the same length. I don't see any test of last modification time. Yes, this suprises me, too. I then went and tested this by modifying only the last modification time of a volume, and it remounted successfully. --Brian Bechtel blob@apple.com "My opinion, not Apple's"