On Tue, 4 Nov 2014 14:30:54 -0800, Charles Mills wrote:

>I always wondered why did they put two more or less mutually-exclusive data
>in two different 12-bit fields? If they had devoted 11 bits to the ABEND
>code and one bit to system versus user, we could have had ABEND codes
>ranging up to S7FFFFF or U8388607. Whether that would have been good or bad
>I will leave as an exercise for the reader.

Once upon a time, the documentation for the ABEND macro specified that the code 
has to be less than 4096. See these excerpts from IBM System/360 Operating 
System Control Program Services, form C28-6S41-1, dated April, 1966. It is 
available on bitsavers at 
http://bitsavers.trailing-edge.com/pdf/ibm/360/os/R01-08/C28-6541-1_Control_Program_Services_Apr66.pdf

<quote from page 102>
compcode
specifies a completion code to be stored in the task completion
code field of the task control block (TCB) of the task issuing the
ABEND...

The value of this operand should be a multiple of 4 and must be
less than 4096. (Refer to "Use of ABEND by Control Program.")
</quote>

<quote from page 104>
Use of ABEND by Control Proqram: When the control program detects an
error condition requiring termination of a task, the control program
issues an ABEND macro-instruction for the task. The completion code
operand value will be from 4096 to 2^24-1 in multiples of 4096.
</quote>

I don't know how the abend code was displayed.

Tom Marchant

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