The Parameter Block

The parameter block contains the addresses of four data objects:

The environment block

The command tail

Two default file control blocks

The space reserved in the parameter block for the address of the environment block is only 2 bytes and holds a segment address. The remaining three addresses are all double-word addresses; that is, they are 4 bytes, with the offset in the first 2 bytes and the segment address in the last 2 bytes.