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RESIDENT MONITOR: Primitive Operating System. Usually in low memory where interrupt vectors are placed. Must check each memory reference against fence ( fixed or variable ) in hardware or register. If user generated address < fence, then illegal. User program starts at fence -> fixed for duration of execution. Then user code has fence address ...
Resident Monitor Holds initial control, control transfers to job and then back to monitor. Problem Need to distinguish job from job and data from program. Principles of Operating Systems - Lecture 1 28 From John Ousterhout slides
With the introduction of the resident monitor, a boundary (fence) address is permanently held by a dedicated fence register. All addresses are checked against the fence address to ensure that the users operate in user (and not monitor) area. Figure 5.2: Illustrating Hardware Protection for Resident Monitor Resident FA
• Computer now has a resident monitor: – initially control is in monitor. – monitor reads job and transfer control. – at end of job, control transfers back to monitor. • Even better: spooling systems. – use interrupt driven I/O. – use magnetic disk to cache input tape. – fire operator. • Monitor now schedules jobs. . .
Resident operating system, usually held in low memory with interrupt vector. User processes then held in high memory. Each process contained in single contiguous section of memory. Relocation registers used to protect user processes from each other, and from changing operating-system code and data.
• One of the first time-sharing operating systems – Developed at MIT by a group known as Project MAC – The system was first developed for the IBM 709 in 1961 – Ran on a computer with 32,000 36-bit words of main memory, with the resident monitor consuming 5000 of that
• Operating system checks if routine is in processes’ memory address, adding it if not • Dynamic loading avoids loading routines until they’re called • Better memory usage as unused routines are never loaded
