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From: spencer@eris.BERKELEY.EDU (Randy Spencer)
Newsgroups: comp.sys.amiga
Subject: Re: Facc From ASDG
Message-ID: <4073@jade.BERKELEY.EDU>
Date: Wed, 24-Jun-87 03:27:53 EDT
Article-I.D.: jade.4073
Posted: Wed Jun 24 03:27:53 1987
Date-Received: Sat, 27-Jun-87 07:45:39 EDT
Sender: usenet@jade.BERKELEY.EDU
Reply-To: spencer@eris.BERKELEY.EDU (Randy Spencer)
Organization: University of California, Berkeley
Lines: 62

In article <1803@vax135.UUCP> cjp@vax135.UUCP (Charles Poirier) writes:
>In article <4024@jade.BERKELEY.EDU> spencer@eris.BERKELEY.EDU (Randy Spencer) writes:
>>>> What I want is a DISK cache.  Facc?  That is a DRIVE cache.  Pop out
>>>> the disk for any reason, and all those lovely buffers are invalidated.
>>
>>Actually, the little magic cookie that lets the computer tell the difference
>>between disks is the last write date on the disk.  So, if I change the
>>disk in my other Amiga, the write date on the disk changes, and when I put
>>it back in my first Amiga the "disk" cache would think it was a different
>>disk and invalidate the old tracks (or at least not use them for this disk).
>
>It would work if all Amigas had a consistent idea of what time it is.
>But many Amigas have no clock.  (And "We don' need no Steeenkin' Setdate!"
>seems to be a pretty common attitude.)
>
>	Charles Poirier   (decvax,ucbvax,ihnp4,attmail)!vax135!cjp

No, you don't understand.  If I have two disks that I copied with
Quickcopy or Marauder, they are *identical*.  The reason that that is
so is the date they were last modified is the same, down to the
milisecond (I guess), so if I boot with one disk, pull it out and put
in the other disk the system will not know the difference.  But if I
write to one disk (or delete, or in any manor change the disk) the
date gets changed, ** and it doesn't matter what it gets changed to **,
but it is different, and at that point the disk would look different
from the first disk to the Amiga.  Boot with one and try to put in the
other one, issue a command and it will ask for the first one again.

     So, we put in our boot disk and run the disk cache.  Some of our
stuff is saved to ram, the stuff that we access often. 

     Then we take out the disk and put in another one, and some of
that gets put in its own disk cache (we still have lots of ram). 

     We put back in the first disk and issue a previous command and
boom!  It runs out of our disk cache and didn't even access the disk. 

     The we put in a third disk which gets is own cache while we take
the first disk out for the second time and place it in another
machine.  When we take it out there delete a file or write a new file. 

     We take that disk and put it into our first machine.  Even though
the disk name is the same, and the disk is really the same disk, the
system looks at it as a different disk.  We cannot pretend that it is
the system disk anymore.  In that same way the disk cache program
thinks of it as a new disk and starts up a NEW cache for it (we are
starting to run out of ram).  If we issue a command from before it
will run it out of the ram cache for the system disk, if its in there,
but otherwise it will not find the disk (and will put up a requester
for it).

  Oh, no, I am talking out of my hat again, I have not tried any of
this, but it seems logical to me.  Well, that will give me something
to do at work tomorrow!
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Randy Spencer      P.O. Box 4542   Berkeley  CA  94704        (415)284-4740 
                         I N F I N I T Y                 BBS: (415)283-5469
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Officially representing  ||||||||||||:::::... ..    ....ucbvax!mica!spencer
                         s o f t w a r e          spencer@mica.berkeley.edu
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