rdisp/vbstart is a SAP Parameter attribute which is used to control Perform initial update requests after start-up information. This is available within R/3 SAP systems depending on the version and release level.
Below is the standard documentation available and a few details of the attributes values .
This parameter controls the start-up behavior of an update server.
During startup the update server checks in its request queue if update
requests exist in it which have not yet been executed (status init). If
this is the case then these requests are selected then executed. This
automatic start can be deactivated by the parameter:
Parameter value 1: The automatic start is active
Parameter value 0: The automatic start is not active
See SAP Parameter Documentation for full SAP documentation for this profile parameter.