Hi Mike - Thank you very much for your reply. I have just another questions. I have put them inline, in the body of your e-mail in *red *color.
On Sat, Nov 17, 2012 at 9:52 PM, Mike Myers <[email protected]>wrote: > Hi Quasar: > > Back in the very beginning (OS/360 MVT in 1971), TSO was introduced. At > that time, it consisted of a "monitor" program which used time-slicing to > distribute the CPU time it was given among the TSO users that were logged > on. > > With the introduction of the System Resource Manager (SRM) in MVS (1974), > things changed. From that point on, "time-sharing" was accomplished by SRM. > In MVS, a TSO user ran in its own address space and became part of a mix of > work units whose CPU usage was controlled by SRM. Any address space was > eligible to be dispatched on a CPU when it was in a "ready" state, the > opposite state can be generalized as a "wait" state. Except for select > address spaces (those marked "non-swappable"), an address space in a wait > state was eligible for swap-out. Entering a wait state could be announced > (long wait) or discovered (detected wait). A TSO user that was inactive (in > between commands or thinking what to do next), was usually in a > terminal-input wait, as a read I/O operation was usually issued to the > terminal when the current command had finished. Thus, the address space > became a candidate for swap-out. > > Because of the unpredictability of the user's actions (how soon after the > swap-out decision was made that they would hit a key and end the I/O wait), > the concept of "think time" and logical swapping was introduced. This was > intended to reduce swap-in I/O activity and the resultant CPU needed to > complete the swap-in. SRM permitted an externally controlled parameter > which represented think-time in seconds, making it possible to allow the > TSO user to remain swapped in for at least that long a period. Once > think-time passed, however, the TSO user could be "logically swapped". > > In the logically swapped state, the pages belonging to the TSO user's > address space would be written to disk or expanded storage (when that was > supported), preparing for physical swapping, but would remain in main > storage until the storage was actually needed to resolve paging demands of > other address spaces. At that point, the TSO address soace would be > physically swapped and it's pages would be made available to the rest of > the system. If the *used became ready (ended the wait) prior to it's > pages being needed*, it would be marked swapped in and would retain use > of its existing pages in main storage. This saved the I/O and CPU time > needed to perform the actual swap in. > How did the SRM know, a TSO Address Space which is in the WAIT state, and logically swapped out, has now transitioned to the READY state after an AID key press? Does the address space send out an *interrupt* to the SRM? And if that's the case, how does it really differ from the transaction monitor CICS? > > In today's version (z/OS) this action still occurs, although we are > inclined to use the component name WLM (WorkLoad Manager) when describing > the functions I have attributed to SRM in the description above. > > Hope this helps. > > Mike Myers > Mentor Services Corporation > > > > On 11/17/2012 05:30 AM, Quasar Chunawala wrote: > >> Hi everybody, >> >> I hope this finds you in the pink of health. I am Quasar, and I hail from >> Mumbai, India. I own a blog on the internet, parked at >> http://www.mainframes360.com. I am an application developer by >> profession. >> >> I intend to write an article on TSO/E on my blog. I have been reading >> matter on time-sharing and its origins on the Internet. I learnt about the >> history of Time Sharing systems and how they evolved over a period of >> time. >> I have also read, Bob Bemer’s article "*How to Consider a Computer*", >> >> published in the Automatic Control Magazine, in March 1957, by . >> >> I would like you to throw some light on the technical underpinnings of >> how TSO really accomplishes the feat of time-sharing. I know that, there >> is >> a TSO address-space for every active user logged on to the system. It is >> my >> understanding that, time is sliced by the scheduler between all the TSO >> jobs, other user-jobs, STARTed tasks etc. But, it occurs to me, why should >> a time-slot be given to a TSO user, who hasn't pressed an AID key(like >> Enter)? Maybe, he's just staring at a dataset. Isn't this a waste of >> processor-time? Or am I missing out something. >> >> Thanks and look forward to receiving a reply from you soon, >> >> Quasar Chunawala >> >> Sent from Windows Mail >> >> ------------------------------**------------------------------** >> ---------- >> For IBM-MAIN subscribe / signoff / archive access instructions, >> send email to [email protected] with the message: INFO IBM-MAIN >> >> > ------------------------------**------------------------------**---------- > For IBM-MAIN subscribe / signoff / archive access instructions, > send email to [email protected] with the message: INFO IBM-MAIN > ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
