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Unformatted text preview: tes & Assignments visit: www.bsit.zxq.net 2.3 x86 Memory Management
Downloaded From: www.bsit.zxq.net 47 same time to be much larger than the computer’s physical memory. The complete collection of
pages mapped by the operating system is called virtual memory. Operating systems have utility
programs named virtual memory managers.
Paging is an important solution to a vexing problem faced by software and hardware designers. A program must be loaded into main memory before it can run, but memory is expensive.
Users want to be able to load numerous programs into memory and switch among them at will.
Disk storage, on the other hand, is cheap and plentiful. Paging provides the illusion that memory
is almost unlimited in size. Disk access is much slower than main memory access, so the more a
program relies on paging, the slower it runs.
When a task is running, parts of it can be stored on disk if they are not currently in use.
Parts of the task are paged (swapped) to disk. Other actively executing pages remain in memory. When the processor begins to execute code that has been paged out of memory it issues a
page fault, causing the page or pages containing the required code or data to be loaded back
into memory. To see how this works, ﬁnd a computer with somewhat limited memory and run
many large applications at the same time. You should notice a delay when switching from one
program to another because the operating system must transfer paged portions of each program into memory from disk. A computer runs faster when more memory is installed because
large application ﬁles and programs can be kept entirely in memory, reducing the amount of
2.3.3 Section Review
1. What is the range of addressable memory in protected mode?
2. What is the range of addressable memory in real-address mode?
3. The two ways of describing an address in real-address mode are segment-offset and
4. In real-address mode, convert the following hexadecimal segment-offset address to a linear
5. In real-address mode, convert the following...
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This note was uploaded on 11/29/2013 for the course CSE 451 taught by Professor Hussein during the Winter '13 term at Fatih Üniversitesi.
- Winter '13