Address Space

Instruction Backup
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Instruction Backup

When a program references a page that is not in memory, the instruction causing the fault is stopped partway through and a trap to the operating system takes place. After the operating system has fetched the page required, it must restart the instruction causing the trap. This

Backing Store
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Backing Store

In our study of page replacement algorithms, we saw how a page is chosen for removal. We have not said much about where on the disk it is put when it is paged out. Let us now explain some of the problems related to disk management. The simplest algorithm for allocating page

Separation of Policy and Mechanism
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Separation of Policy and Mechanism

An important tool for managing the complexity of any system is to separate policy from mechanism. This principle can be applied to memory management by having most of the memory manager run as a user-level process. Such a separation was first done in Mach (Young et al.,

SEGMENTATION
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SEGMENTATION

The virtual memory discussed so far is one-dimensional because the virtual addresses go from 0 to some maximum address, one address after another. For various problems, having two or more separate virtual address spaces may be much better than having only one. For

Segmentation with Paging: MULTICS
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Segmentation with Paging: MULTICS

If the segments are large, it may be inconvenient, or even impossible, to keep them in main memory in their entirety. This leads to the idea of paging them, so that only those pages that are really required have to be around. Many significant systems have supported paged

file-systems
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file-systems

All computer applications need to store and get back information. While a process is running, it can store a limited amount of information within its own address space. On the other hand, the storage capacity is restricted to the size of the virtual address space. For some

Memory-Mapped I/O
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Memory-Mapped I/O

Each controller has a few registers that are used for communicating with the CPU. By writing into these registers, the operating system can command the device to deliver data, accept data, switch itself on or off, or otherwise perform some action. By reading from these registers,

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