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3.4 System Software (Memory Management (Paging - Process address space is…
3.4 System Software
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OS
In the ROM, the (BIOS) starts a bootstrap program that loads the
OS into memory and sets it running.
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User Interface - Provide device drivers, file system for a user to store data.
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Scheduling
Non-preemptive - once a process runs, it cannot be preempted until it completes its allotted time.
First-Come, First-Served (FCFS)
Priority - Process w/ highest priority is executed first. Processes w/ same priority are executed on FCFS basis. Priority is based on memory or time requirements.
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Interrupt
Hardware & Software
- CPU receives an interrupt. 2. PC contents saved in stack. Registers' content also saved. 3. ISR loaded and run. 4. Restore registers' content.
Memory Management
Segmentation - each job is divided into several segments of different sizes. Allows programs and data to be broken up into logically independent address spaces
Paging - Process address space is broken into blocks of the same size called pages.
Similarly, main memory is divided into frames. Frames and Pages have identical size to have optimum utilization of the main memory and to avoid external fragmentation.
A page map table is used to keep track of the relation between a page of a process to a frame in physical memory.
Disk thrashing - virtual memory subsystem is in a constant state of paging. This causes performance degradation.
Virtual memory: a paging mechanism that allows a program to use more memory addresses than are
available in main memory.