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Operating System Support (Desirable Hardware Features (Memory Protection…
Operating System Support
OS Services
It is the most important system program. It masks the hardware of the device and provides the user with an interface to use the system.
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Segmentation
It is visible to the programmer. It allows the programmer to view the memory as multiple address spaces or segments.
It simplifies the handling of growing data structures. It lends itself to sharing among processes and to protection.
Pentium II
Each virtual address consist of 16bit segment and 32bit offset. Physical address uses a 32 bit address for a maximum of 4GB. Unsegmented memory = 4GB and Segmented Memory = 64 TB.
Protection
There are two forms of protection: Privilege level and Access Attribute. Also there are 4 privilege levels from level 0(most protected) to level 3(least protected).
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Scheduling
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Medium-Term Scheduling
It is part of the swapping function. Swapping decision is made based on the need to manage the multiprogramming.
Short-Term Scheduling
It is known as the dispatcher. It executes frequently and makes the decision on which job to execute.