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Topic: Virtual memory

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Disk swapping

Memory management

Multiprogramming

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Computer memory

Operating system kernel

Microcode

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Operating system

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	Virtual Memory and its influences on performance
		While virtual memory makes it possible for computers to more easily handle larger and more complex applications, as with any powerful tool, it comes at a price.
		This means that performance will never be as good with virtual memory than with the same application that is 100% memory-resident.
		From this, the overall point to keep in mind is that the performance impact of virtual memory is minimal when it is used as little as possible.
	www.computermemoryupgrade.net /virtual-memory-influence-on-performance.html (387 words)

	Howstuffworks "How Virtual Memory Works"
		Virtual memory is a common part of most operating systems on desktop computers.
		In this article, you will learn exactly what virtual memory is, what your computer uses it for and how to configure it on your own machine to achieve optimal performance.
		Please close another application to load a new one." With virtual memory, what the computer can do is look at RAM for areas that have not been used recently and copy them onto the hard disk.
	computer.howstuffworks.com /virtual-memory.htm (504 words)

	Reference.com/Encyclopedia/Virtual memory
		Memory can be addressed that does not currently reside in main memory and the hardware and operating system will load the required memory from auxiliary storage automatically, without any knowledge of the program addressing the memory, thus allowing a program to reference more memory than actually exists in the computer.
		Virtual memory was introduced to the x86 architecture with the protected mode of the Intel 80286 processor.
		Virtual memory has been a feature of Microsoft Windows since Windows 3.0 in 1990; it was done in an attempt to slash the system requirements for the operating system in response to the failures of Windows 1.0 and Windows 2.0.
	www.reference.com /browse/wiki/Swap_file (2013 words)

	Virtual memory - Wikipedia, the free encyclopedia
		Virtual memory or virtual memory addressing is a memory management technique, used by multitasking computer operating systems wherein non-contiguous memory is presented to a software (aka process) as contiguous memory.
		To properly implement virtual memory the CPU (or a device attached to it) must provide a way for the operating system to map virtual memory to physical memory and for it to detect when an address is required that does not currently relate to main memory so that the needed data can be swapped in.
		Virtual memory was developed in approximately 1959 - 1962, at the University of Manchester for the Atlas Computer, completed in 1962.
	en.wikipedia.org /wiki/Virtual_memory (3027 words)

	Virtual Memory Definition (Site not responding. Last check: )
		Memory is used to hold portions of the operating system, programs and data that are currently in use or that are frequently used.
		Virtual memory was incorporated into the UNIX kernel (i.e., the core of the operating system) in the 1970s as part of the Berkeley Extensions, which were developed at the University of California at Berkeley (UCB).
		Virtual memory is so important that its acronym, i.e., vm, was incorporated into the name of the Linux kernel as it is used on most systems, i.e., vmlinux for the non-compressed version and vmlinuz for the compressed, bootable (i.e., runnable) version.
	www.bellevuelinux.org /virtual.html (806 words)

	Virtual Memory and Demand Paging: ASP Alliance
		Virtual Memory allows a program of larger size than available memory to be loaded and executed by loading the same in parts.
		Â Virtual Memory is a concept that addresses this issue by allowing a program than is even larger than the size of the available free memory to be loaded and executed and eliminate the chances of external fragmentation.
		In virtual memory systems, demand paging is a type of swapping in which pages of data are not copied from disk to RAM until they are needed.
	aspalliance.com /969_Virtual_Memory_and_Demand_Paging (2265 words)

	Smart Computing Encyclopedia Entry - virtual memory (Site not responding. Last check: )
		Virtual memory is actually a reserved portion of the hard drive that mimics RAM when actual memory space is limited.
		Virtual memory attempts to ease this problem by taking advantage of hard drive space.
		To do this, the OS keeps track of where data is located in the main memory and stores the addressing information in the cache, where it’s readily accessible to the processor.
	www.smartcomputing.com /editorial/dictionary/detail.asp?searchtype=2&DicID=19486&RefType=Encyclopedia&guid= (414 words)

	Video editing system having virtual memory - Patent 4754342
		A virtual memory system for a video editor is disclosed which permits edited material from discrete takes to be electronically spliced in real time to form edited scenes.
		It is an object of this invention to disclose a virtual memory scheme enabling playback of a series of edited takes in any direction, at variable speed so that the performance of a work print fully spliced is electronically emulated.
		An advantage of the disclosed virtual memory technique is that a disk control protocol is disclosed which enables a video edit to replay in the same manner as spliced film.
	www.freepatentsonline.com /4754342.html (5739 words)

	CHOICE - Windows virtual memory (archived)
		Virtual memory is a part of your hard drive that acts as though it’s RAM.
		Because of the way virtual memory works, it’s also known as the swap file or paging file; Virtual memory ensures that only the most essential information is kept in RAM where it can be accessed quickly, so it can make a big difference to your computer’s performance while running more than one program simultaneously (multi-tasking).
		If changing virtual memory settings doesn’t solve your problems, it may be because there’s simply not enough hard drive space or RAM for virtual memory to function properly.
	www.choice.com.au /goArticle.aspx?id=103893&title=Windows+virtual+memory+(archived) (540 words)

	Technical Note TN1094: Virtual Memory Application Compatibility
		This is in contrast with memory in the system heap, which is automatically held in the current VM implementation.
		Virtual Memory requires services which are not present in the ROMs of 68000-based machines, so VM is not supported on the Macintosh SE, even one with a 68030 accelerator.
		Virtual Memory depends on low-memory globals to indicate the presence of a memory management unit at a very early stage of the boot process.
	developer.apple.com /technotes/tn/tn1094.html (5407 words)

	Method to automatically increase the segment size of unix files in a page segmented virtual memory data processing ...
		The prior art also discloses a number of multi-tasking virtual memory data processing systems in which the system architecture is based on establishing a different "virtual machine" or terminal for each of the applications that are run concurrently on the system.
		The virtual memory paging system automatically takes care of the physical I/O. However, references beyond the end of the file cause a problem as do references to so-called "holes" in the file which exist because the segment is a sparse-type file or a portion of the file has been intentionally deleted.
		The Virtual Memory Manager utilizes this by attempting to allocate on the paging space whose point of last allocation is closest to where the disk arm is (for all disks).
	www.freepatentsonline.com /4761737.html (11889 words)

	Virtual Memory
		Basically, once the virtual address is translated to a physical address, then the physical address is passed to the cache, which checks to see if there is a cache hit.
		Virtual memory is handled partly by hardware (translation mechanism) and partly by the operating system (sets up page table, handles page faults, etc).
		With virtual memory, the management of disk as an extension of RAM is handled automatically.
	www.cs.umd.edu /class/spring2003/cmsc311/Notes/Memory/virtual.html (2995 words)

	Smart Computing Article - Manage Windows 98 Virtual Memory (Site not responding. Last check: )
		Virtual memory is an important contributor to Windows 98’s reliability and performance.
		When the amount of memory Win98 needs exceeds the amount that’s available, data in RAM you haven’t recently accessed is copied to virtual memory on the hard drive.
		But virtual memory is a substitute for physical memory, so the two have an inverse relationship.
	www.smartcomputing.com /usercheck.asp?to=%2Feditorial%2Farticle%2Easp&article=articles%2F2005%2Fs1609%2F09s09%2F09s09%2Easp&articleid=27682&guid=&searchtype=0&WordList=&bJumpTo=True (1541 words)

	CS322: Virtual Memory
		Even if physical memory were large enough to hold any process that might be run on a given system, virtual memory can still be advantageous by allowing more processes to be (partially) memory resident at once, thus allowing for higher utilization of the CPU and/or allowing more interactive users to be online.
		In a virtual memory system, we no longer require that all of the pages belonging to a process be physically resident in memory at one time.
		In practice, however, this does not often occur, since virtual memory systems are generally multiprogrammed and thus are configured with sufficient physical memory to allow portions of many processes to be resident at once.
	www.cs.gordon.edu /courses/cs322/lectures/virtual_memory.html (5393 words)

	redhat.com \| Red Hat Magazine - Understanding Virtual Memory
		Virtual Memory (VM) allows an operating system to perform many of its advanced functions, such as process isolation, file caching, and swapping.
		A page fault is encountered every time a virtual memory address is accessed for which there is not yet a corresponding physical page assigned or for which the corresponding physical page has been swapped to disk.
		If the memory address has been requested in a valid way (for example, the application contains the address in its virtual memory map), then the kernel associates a page of RAM with the address or retrieves the page from disk and places it back in RAM.
	www.redhat.com /magazine/001nov04/features/vm (3835 words)

	Basic Virtual Memory Concepts
		In other words, an overlayed program may require less memory to run than a program that is not overlayed, but if the system still does not have sufficient memory for the overlayed program, the end result is the same — an out of memory error.
		Virtual memory turns the concept of an application's address space on its head.
		This is done by structuring the virtual memory subsystem so that it attempts to ensure that those parts of the application currently needed — or likely to be needed in the near future — are kept in RAM only for as long as they are actually needed.
	www.centos.org /docs/rhel-isa-en-3/s1-memory-concepts.html (768 words)

	virtual memory (Site not responding. Last check: )
		Each virtual address output by the CPU is split into a (virtual) page number (the most significant bits) and an offset within the page (the N least significant bits).
		The offset is left unchanged and the memory management unit (MMU) maps the virtual page number to a physical page number.
		Similarly, a multitasking system might load the whole program and its data into physical memory when it is to be executed and copy it all out to disk when its timeslice expired.
	burks.brighton.ac.uk /burks/foldoc/72/124.htm (434 words)

	Virtual Memory
		Given a memory address (an instruction to fetch, or data to load or store), the processor first looks in the TLB to determine if the mapping of virtual page to physical page is already known.
		If the valid bit is clear or if the virtual page is not found in the TLB, software translation is needed to tell whether the the page is in memory (with the TLB to be loaded with the translation), or the page must be brought in from disk.
		For this virtual memory assignment the documentation should include a description of your virtual memory architecture and the page and TLB replacement policies you selected.
	www.cs.rit.edu /~icss544/VirtualMemory.html (1602 words)

	How Can I Fix “Too Little Virtual Memory” In Windows? ~ Windows Fanatics
		A memory leak is a common problem caused by poorly written or poorly debugged applications where they continually use more and more memory until you shut down the program, end the process manually or restart Microsoft Windows.
		Virtual memory, also known as a page file or swap file, is a file on your hard drive (C:\pagefile.sys by default) that Windows and applications use in addition to physical memory (RAM) as needed.
		Virtual memory is the sum of physical memory and the page file.
	www.lockergnome.com /nexus/windows/2005/04/22/how-can-i-fix-too-little-virtual-memory-in-windows (468 words)

	OSD: Virtual memory (Site not responding. Last check: )
		This means the virtual addresses generated by a program are different from the physical addresses that go onto the address bus; to the memory chips.
		The task virtual memory is private to each task; the identity-mapped and kernel virtual memory are shared among all tasks.
		Since memory fragmentation is not an issue for these, they may be stored in identity-mapped memory or kernel virtual memory, whichever is more convenient.
	my.execpc.com /CE/AC/geezer/osd/mem (1382 words)

	TweakHound - Understanding Virtual Memory
		When the operating system needs to claim memory, (because all memory is currently in use, and you are launching new apps, or loading more info into existing work), the OS obviously has to get the necessary ram from somewhere.
		Now, for users that do not put their memory under pressure, if you are certain you won't be adding additional workload, you will not likely take a hit if you decide to lower the default setting of the page file.
		In the simplest terms this is when your work is asking for more virtual memory (commit charge) than what the OS is prepared to deliver (commit limit).
	www.tweakhound.com /xp/virtualmemory.htm (2513 words)

	Memory, Virtual Memory, Laptop Memory, Corsair Memory, Viking Memory, Cisco Memory, Memory Chips, Memory Enhancer, ...
		virtual memory During the shock and ride into the presentation you a.
		memory As she doubted it was the rooms whisked clean of.
		virtual memory Gabrielle had about a locket in the house and she.
	huivam.blog.kataweb.it /memory-413.html (3448 words)

	Virtual Memory: The Details
		Virtual address space depends on the architecture because it is the architecture that defines how many bits are available for addressing purposes.
		Virtual address space also depends on the operating system because the manner in which the operating system was implemented may introduce additional limits over and above those imposed by the architecture.
		To implement virtual memory, it is necessary for the computer system to have special memory management hardware.
	www.centos.org /docs/rhel-isa-en-3/s1-memory-virt-details.html (947 words)

	Virtual Memory
		Whenever a process has a page fault, print the address space that caused the fault, which virtual page number the fault was for, and the physical page frame that was used to satisfy the fault.
		Of course, the memory manager looks at the page table entry for that frame (via the ``space'' pointer) to determine if a page has been used recently, is modified, etc.
		For example, the routine LockMemory() might take a virtual address and length, insure that all pages corresponding to the specified addresses indicated are loaded and present in physical memory and lock them into place.
	www.cs.duke.edu /~narten/110/nachos/main/node34.html (1595 words)

	virtual memory
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	www.virtualhelper.org /virtual-memory (1673 words)

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