The TCB in OS/360 and successors
In OS/360, OS/VS1, SVS,Request Blocks
OS/360 has the following types of request blockss ; Interruption Request Block : An IRB is used to handle an asynchronous exit. ; Program Request Block : A PRB represents a module invoked with an ATTACH macro, a LINK macro or a synchronous exit. ; System Interruption Request Block : An SIRB is used to run I/O error recovery code. ; Supervisor Request Blocks : An SVRB represents the execution of a Type 2, Type 3 or Type 4 SVC routine An RB contains several fields, among the na old PSW, old general registers, a PSW and a wait count.Dispatching
The ''Dispatcher'' is a routine in the nucleus that selects the work to be dispatched. It selects the highest priority task that: #Is not running on another CPU #Does not have any non-dispatchability flags set #Has a top RB with a zero wait count. The system maintains a pair of TCB pointers known as TCB old and TCB new. A TCB new pointer of zero causes the dispatcher to search for an eligible task. When the dispatcher finds an eligible task, it sets the old and new TCB pointers. loads the registers from the TCB and loads the PSW from the top RB. If the dispatcher fails to find eligible work, it enters an enabled wait.History
With the introduction ofSee also
* Process control blockNotes
References
{{reflist, refs= {{cite manual , title = IBM System/360 Operating System - Fixed-Task Supervisor - Program Number 360S-CI-505 , id = Y28-6612-2 , date = February 1967 , edition = Third , url = http://www.bitsavers.org/pdf/ibm/360/os/plm_1966-67/Y28-6612-2_Fixed-Task_Supervisor_PLM_Sep67.pdf , work = Program Logic , access-date = {{cite manual , title = IBM System/360 Operating System - MVT Supervisor , id = GY28-6659-7 , date = May 1973 , edition = Eighth , url = http://bitsavers.org/pdf/ibm/360/os/R21.7_Apr73/plm/GY28-6659-7_MVT_Supervisor_PLM_Rel_21.7_May73.pdf , work = Program Logic , access-date = March 14, 2022 {{cite manual , publisher = IBM , title = IBM System/360 Operating System: System Control Blocks - OS Release 21.7 , id = GC28-6628-9 , edition = Tenth , date = April 1973 , url = http://bitsavers.org/pdf/ibm/360/os/R21.7_Apr73/GC28-6628-9_OS_System_Ctl_Blks_R21.7_Apr73.pdf , work = Systems Reference Library , access-date = June 12, 2022 Process (computing)