How Unix implements virtual memory?


 
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Homework and Emergencies Homework & Coursework Questions How Unix implements virtual memory?
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Old 09-03-2009
Computer How Unix implements virtual memory?

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1. The problem statement, all variables and given/known data:
The key to using memory most efficiently is virtual memory management. Consider both Windows and UNIX operating systems. Compare and contrast how each implements virtual memory. Describe how each one handles page faults, working sets, and page sizes, and how it reconciles thrashing issues. Cite your sources.


2. Relevant commands, code, scripts, algorithms:
there are no commands required.


3. The attempts at a solution (include all code and scripts):
no solution.


4. School (University) and Course Number:
Mapua Institute of Technology - Information Technology
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mem(7D) 							      Devices								   mem(7D)

NAME
mem, kmem, allkmem - physical or virtual memory access SYNOPSIS
/dev/mem /dev/kmem /dev/allkmem DESCRIPTION
The file /dev/mem is a special file that provides access to the physical memory of the computer. The file /dev/kmem is a special file that provides access to the virtual address space of the operating system kernel, excluding memory that is associated with an I/O device. The file /dev/allkmem is a special file that provides access to the virtual address space of the operating system kernel, including memory that is associated with an I/O device. You can use any of these devices to examine and modify the system. Byte addresses in /dev/mem are interpreted as physical memory addresses. Byte addresses in /dev/kmem and /dev/allkmem are interpreted as kernel virtual memory addresses. A reference to a non-existent location returns an error. See ERRORS for more information. The file /dev/mem accesses physical memory; the size of the file is equal to the amount of physical memory in the computer. This size may be larger than 4GB on a system running the 32-bit operating environment. In this case, you can access memory beyond 4GB using a series of read(2) and write(2) calls, a pread64() or pwrite64() call, or a combination of llseek(2) and read(2) or write(2). ERRORS
EFAULT Occurs when trying to write(2) a read-only location (allkmem), read(2) a write-only location (allkmem), or read(2) or write(2) a non-existent or unimplemented location (mem, kmem, allkmem). EIO Occurs when trying to read(2) or write(2) a memory location that is associated with an I/O device using the /dev/kmem spe- cial file. ENXIO Results from attempting to mmap(2) a non-existent physical (mem) or virtual (kmem, allkmem) memory address. FILES
/dev/mem Provides access to the computer's physical memory. /dev/kmem Provides access to the virtual address space of the operating system kernel, excluding memory that is associated with an I/O device. /dev/allkmem Provides access to the virtual address space of the operating system kernel, including memory that is associated with an I/O device. SEE ALSO
llseek(2), mmap(2), read(2), write(2) WARNINGS
Using these devices to modify (that is, write to) the address space of a live running operating system or to modify the state of a hardware device is extremely dangerous and may result in a system panic if kernel data structures are damaged or if device state is changed. SunOS 5.10 18 Feb 2002 mem(7D)

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