gtpm6m0aMain Supervisor Reference

Initializing Main Storage

The programs that initialize main storage, referred to collectively as the initializer, receive control directly from the IPL program.

The initializer is a stand-alone CSECT, CCCTIN, which does not need to access tape or disk data. All of the necessary information is maintained in the keypoint records and essential control program records. The IPL program passes the initializer a parameter list that contains the addresses of the records. The initializer must be executed before ECB-controlled programs can use control program services. (Refer to Controlling E-Type Programs for a description of ECB-controlled programs.)

The initializer sets up all fixed and working main storage. The main storage allocation programs then control the dynamic use of working storage (see Managing Storage).

Low-Address Protection

Low-address protection is a hardware facility that protects the first 512 bytes of each CPU's page 0 -- the part of storage most apt to be corrupted by programs. Neither applications nor the TPF control program can modify this storage while low-address protection is active.

Low-address protection is turned on by IPLB. Programs that modify the first 512 bytes of memory can use the LCPCC macro to turn low-address protection off (and on again). Commands that alter main storage (such as ZACOR and ZAPGM) turn off low-address protection internally.