Software Errors

Examples of software errors are:
  • A program has an error in its logic.
  • A program contains incorrect data definitions.
  • A program wants to process a file that is not defined to the system.
  • An entry is missing in a system table.

Because of a software error a program may come to an abnormal end ('abend' for short) and may be canceled. A software error may also cause incorrect output, a loop or a wait condition.

LOOP

A loop in a program is any repetitive execution of a sequence of instructions. Frequently, repetitive execution of a part of a program is intentional. Sometimes, however, a program incorrectly executes a sequence of instructions over and over again. The cause is, in most cases, a logic error; usually in an application program or sometimes in an IBM-supplied program. In exceptional cases a hardware malfunction may also be the cause of a loop.

WAIT

There are several kinds of waits and not all of them are error conditions. When the system (processor) stops processing, the processor is in a wait state. For example, the processor waits for an answer from an I/O device, or there is nothing to process because no program is active. Note, however, that the system wait state does not indicate the wait status of a partition.

Sometimes, an error in an application program, in a control program, or a device causes the processor to stop. Such a condition is a hard wait if the processor is unable to recover. Only a new startup (IPL) will reactivate the system. In another error situation the system will resume operation after the cause for the wait (for example, a device was not ready) has been removed. This type of wait is a soft wait.
Note: Errors often arise when the system setup is changed; devices are added or deleted, or new programs or applications are installed. Therefore, changes to the system should be carefully planned and documented. Refer to Change Log for further details on documenting system changes.