Path: utzoo!mnetor!uunet!portal!cup.portal.com!dick_a_wotiz
From: dick_a_wotiz@cup.portal.com
Newsgroups: comp.os.cpm
Subject: Re: CP/M disk Directories
Message-ID: <3882@cup.portal.com>
Date: 13 Mar 88 18:01:57 GMT
References: <2662@crash.cts.com>
Distribution: na
Organization: The Portal System (TM)
Lines: 39
XPortal-User-Id: 1.1001.1002


> Ok, all you CP/M mavens, here's a good question for you.  Not anything earth-
> shattering, or anything like that... just irritating.
> 
>  . . . .
> 
>                                 vv-------------- extent #1?
>                                 vv    vv-------- 80h records in this
>                                 vv    vv         extent?
>                                 vv    vv
> 60  00544553 54202020  2046494C 01000080  |.TEST    FIL....|
> 70  090A0B0C 0E0F101E  393A3B4E 5C5D5E5F  |........9:;N\]^_|
> 
>                                 vv-------------- extent #3?
>                                 vv    vv-------- 7fh records in this
>                                 vv    vv-------- extent?
>                                 vv    vv
> 00  00544553 54202020  2046494C 0300007F  |.TEST    FIL....|
> 10  60616263 64656667  686E6F70 71727374  |`abcdefghnopqrst|

   Actually, the byte you are calling the 'extent #' is handled a
little differently.  The LSB of this byte means 'add 80h records to
the record count byte', and the upper 7 bits, when shifted once to
the right, are the extent number.

   The '# of records' byte is never allowed to get larger than 80h,
so this method is needed to allow up to 256 records per extent.

Some examples:                    vv    vv
      extent 0,  127 records:     0000007F
         "       128 records:     00000080
         "       129 records:     01000001
         "       256 records:     01000080
      extent 1,  1   record:      02000001
         "       129 records:     03000001
         "       255 records:     0300007F

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     dick@portal.com                {uunet|sun|atari}!portal!dick
     dick@cup.portal.com