What is PSB & ACB?

PSB : Program specification block. Inform about how a specific program is to be access one or more IMS DB.

It consists of PCB(Prg Communication Block). Information to which segment in DB can be accessed, what the program is allowed to do with those segment and how the DB is to be accessed.

ACB : Access Control Blocks are generated by IMS as an expansion of information contained in the PSB in order to speed up the access to the applicable DBD's.