Wirt,
I find it amazing that an explanation like "D means debit and C means
credit" which you "heard somewhere" is something to which you would
cling so tenaciously.  Keep in mind that this is IBM we are talking
about - Occam's Razor does not apply.  Jeff's explanation is the one I
have always believed, and I believe it makes much more sense.  In fact,
it answers your question "Where does the F come from" far better than
your explanation does.  I believe the debit/credit stuff is probably
just a mnemonic device someone came up with to help them remember which
is which.

John Clogg

-----Original Message-----
From: HP-3000 Systems Discussion [mailto:[log in to unmask]] On
Behalf Of Wirt Atmar
Sent: Friday, November 25, 2005 3:45 PM
To: [log in to unmask]
Subject: Re: Packed Fields

Jeff writes:

> EBCDIC character hex codes are not contiguous like ASCII, and follow
more 
> closely to the Hollerith codes as above.  Thus we have the EBCDIC 
characters 
> C1-C9 being "A"-"I" and D1-D9 being "J"-"S" as in Glenn's example.  
>  
>  The IBM didn't operate on zoned decimal natively, you had to convert
to 
and 
> from packed decimal.  But this didn't quite yet dictate the sign
nibble.
>  
>  PACK instruction packed the low-order nibbles of the zoned bytes into

> consecutive nibbles of the packed field, and stuck the high-order
nibble of 
> the last byte into the last nibble of the packed field.

Not only is your explanation excessively complex, I think that you're
missing 
the point: BCD encodings have nothing to do with EBCDIC or ASCII or even

Swahilli. There are only sixteen bit encodings possible and if you're
going to 
indicate a numeric sign, you're going to have to pick two (or three) of
the 
remaining six non-numeric characters to do so.

While in my youth I overpunched with the best of them, overpunching
isn't 
possible with only sixteen characters, thus a distinct nibble has to be
allocated 
if you want to record the sign of the number. The fact that you can find
some 
correlation with the sequence of characters between BCD and EBCDIC isn't

surprising. The BCD part is right there in the name, but the same sort
of 
correlation exists in ASCII as well. People, even if working completely
independently, 
would simply tend to put characters in the same order time after time.

Wirt Atmar

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