Re: Odd/Even packed numbers.

[Neil Palmer <neilp@xxxxxxxxxxx>]

Data on disks is written in sectors,  at one point it was 256 bytes/sector
- but larger sector sizes are multiples or 256, therefore in the old days,
accessing a record with a 256 byte length would require reading one
physical disk sector (a record length of 64 would yield 4 records per
sector or access with no additional overhead).  A record length of 257
would require reading 2 physical disk sectors to read one record, hence
much more inefficient.

...Neil





Vern Hamberg <vhamberg@centerfieldtechnology.com>



        To:     midrange-l@midrange.com
        cc:
        Subject:        Re: Odd/Even packed numbers.


OK, Neil, I'm not even as much a codger as some of you - what was the
issue
with 257 or 260 record lengths - looks very close to 256.

Thanks, esp. as this will tell me how much better off I am today.  ;-)

Vern

At 01:11 AM 11/29/02 -0500, you wrote:
>Yes, but you still can end up with additional unnecessary disk accesses
>when that happens.
>
>To clarify my point, I actually did see a new programmer create a file
>with a record length of 260 once - but the real killer was they had added
>a 10 byte "filler" field to the end of what was actually only 250 bytes
of
>data.  ;-)
>
>...Neil
>
>PaulMmn <PaulMmn@ix.netcom.com>
>
>         To:     midrange-l@midrange.com
>         Subject:        Re: Odd/Even packed numbers.
>
>I haven't worried about file record lengths (or pack maps, for that
>matter) since we converted from the S/360/20/5 to the S/3/15-- which knew
>how to span records of strange length across sector boundaries.
>
>--Paul E Musselman
>PaulMmn@ix.netcom.nospam.com
>
> >True - but I still cringe when I see some new programmer create a new
> file with a record length like 257 !  ;-)
> >
> >...Neil