How many ways a background job can be scheduled in SAP

Based on general data:

priority 1: Class A job with target servers(group).
priority 2: Class A job without target server (group).
priority 3: Class B job with target server (group).
priority 4: Class B job without target server (group).
priority 5: Class C job with target server( group).
priority 6: Class C job without target server (group).

• in some situation very long running Background jobs need to be schedule in "CLASS C"

 Note: if at a time all the job from priority 1 to priority 6 are scheduled. first job will be executed is Priority1 --> followed by -->  priority 2 --> followed by --> priority 3 --> followed by --> priority 4 --> followed by --> priority 5 --> followed by --> priority 6.

Based of steps data:

1. ABAP program as background job.
2.  ABAP program with variant.
3. External command.
4. External program.

Based on start period:

1. Immediate background job.
2. Scheduled (At a particular date and time).
3. Periodic job. eg: every day at 4pm.
4. After job.
5. After event.
6. At operation mode.
7. periodic job with some exceptions based on company calender

From SAP point of view, background jobs are of 2 types:

1. standard job or house keeping jobs.
2. customizing  jobs.