How Memory Is Implemented in a Modern Operating System - Essay Example

Investigation of How Memory Is Implemented In a Modern Operating System Such As WindowsXP Microsoft Corporation recommends that computers running Windows XP have at least 128 megabytes (MB) of Random Access Memory (RAM) installed. For this memory size, Windows XP has shown itself to be consistently superior to previous versions of Windows. Performance only gets better with additional resources, particularly when you run memory-intensive multimedia applications. Many users will want to expand their computer's memory to take advantage of multimedia applications and to achieve even better performance. In general, adding memory is the easiest and most effective way to improve a computer's performance. Although it is recommended, Windows XP does not require 128 MB of RAM. (Sechrest and Fortin 2001) Memory Size Usually a modern operating system can run with 64 MB of RAM. For many workloads that involve Web browsing, e-mail, and other activities, 64 MB of RAM will provide user with stability but not speed. Although operating systems like Linux or FreeBSD show better performance having 64 MB of RAM, Windows XP is able to run on the same hardware. (Bott, Siechert, and Stinson 2004). Laskin (n.d.) writes that 128Mb was simply not enough to allow Windows XP to operate efficiently. He observed an average increase in speed of 25% between 128Mb and 256Mb. The next step up in his investigation was 512Mb. Here the increase was less dramatic but still quite noticeable, about a 5% increase in speed depending on the test. Whilst extra memory can affect the overall speed, Lackey (n.d.) writes, it can also make for smoother operation depending on the task in hand. Basic word processing and Internet access usually require no more then 128-256Mb of RAM. More demanding tasks can soon show the inadequacy of low amounts of RAM. Graphics and Sound are the two memory consumers. Complex documents containing graphics or embedded charts and especially more sophisticated PowerPoint presentations are much easier to handle with between 256and 512Mb. Databases start to benefit too at this level. In fact, the more RAM the better when it comes to these as they can keep their temporary tables in memory speeding up performance immensely. The real memory consuming tasks include 3D work, both CAD (Computer Aided Design) and more generalized computer graphics, real time video editing and real world modeling such as water flow calculations. Here the sky is the limit with 1Gb or more not being at all unreasonable. Most people who Lackey (n.d.) knows work with 3D graphics professionally tend to run at their systems maximum, usually 4Gb. Addressing of Memory in Windows XP As Nichol (2006) writes, a program instruction in a modern operating system on an Intel 386 or later CPU can address up to 4GB of memory, using its full 32 bits. This is normally far more than the RAM of the machine. So the hardware provides for programs to operate in terms of as much as they wish of this full 4GB space as Virtual Memory, those parts of the program and data which are currently active being loaded into Physical Random Access Memory (RAM). The processor itself then translates ('maps') the virtual addresses from an instruction into the correct physical equivalents, doing this on the fly as the instruction is executed. The processor manages the mapping in terms of pages of 4 Kilobytes each - a size that has implications for managing virtual memory by the system. Page File By Nichol (2006), only those parts of the program and data that are currently in active use need to be held in physical RAM. Other parts are then held in a page file (in Windows NT versions including Windows 2000 and XP: pagefile.sys). When a program tries to access some address that is not currently in physical RAM, it generates an interrupt, called a Page Fault. This asks the system to retrieve the 4 KB page containing the address from the page file (or in the case of code possibly from the original program file). This - a valid page fault - normally happens quite invisibly. Sometimes, through program or hardware error, the page is not there either. The system then has an 'Invalid Page Fault' error. This will be a fatal error if detected in a program: if it is seen within the system itself (perhaps because a program sent it a bad request to do something), it may manifest itself as a 'blue screen' failure with a STOP code. If there is pressure on space in RAM, then parts of code and data that are not currently needed can be 'paged out' in order to make room - the page file can thus be seen as an overflow area to make the RAM behave as if it were larger than it is. Items in RAM can be divided into: The Non-Paged area. Parts of the System which are so important that they may never be paged out - the area of RAM used for these is called in XP the 'Non-Paged area'. Because this mainly contains core code of the system, which is not likely to contain serious faults, a Blue Screen referring to 'Page Fault in Non-Paged area' probably indicates a serious hardware problem with the RAM modules, or possibly damaged code resulting from a defective Hard disk. It is, though, possible that external utility software (e.g. Norton) may put modules there too, so if such faults arise when you have recently installed or updated something of this sort, try uninstalling it. The Page Pool which can be used to hold: Program code, Data pages that have had actual data written to them, and A basic amount of space for the file cache (known in Windows 9x systems as Vcache) of files that have recently been read from or written to hard disk. Any remaining RAM will be used to make the file cache larger. (Nichol 2006) The page file is created during the Windows XP installation and resides on the hard drive. Page files are measured in megabytes. The size of the page file is based on how much RAM is installed in the computer. By default, XP creates a page file which is 1.5 times the amount of installed RAM and places it on the hard drive where XP is installed. Other than plugging the RAM into the motherboard, there is little than can be done to alter its performance characteristics. The page file is a different story. Because it's located on a hard drive, it's subject to a number of factors that can hinder its performance. (Bott, Siechert, and Stinson 2004). Problems with Memory in Windows XP It may sometimes happen that the system gives 'out of memory' messages on trying to load a program, or give a message about virtual memory space being low. Nichol (2006) names following possible causes of this: The setting for Maximum Size of the page file is too low, or there is not enough disk space free to expand it to that size The page file has become corrupt, possibly at a bad shutdown The page file has been put on a different drive without leaving a minimal amount on the drive C: There is trouble with third party software Possibly there is trouble with the drivers for IDE hard disks With an NTFS file system, the permissions for the page file's drive's root directory must give "Full Control" to SYSTEM. If not, there is likely to be a message at boot that the system is "unable to create a page file." (Nichol 2006) Some of XP's own features can use lots of memory that could also cause problems. Windows XP has a feature called Fast User Switching that lets two or more users use the PC whilst leaving the previous person's settings intact as well as their programs left running. If several people run different programs this way, the machine will effectively have dozens of programs in RAM increasing the need for more memory. Some sources cite a rule of thumb of 64Mb per person so if 3 people use a PC, allow 3 X 64Mb or 192Mb as a minimum. Lackey's (n.d.) finding would suggest that 64Mb might be too conservative though so you may consider 128Mb per person a more productive amount. Another thing to be aware of is that Windows XP constantly tweaks itself internally depending on the resources it has and a machine with insufficient RAM can sometimes decide to shutdown such features as speech recognition to claw back RAM. Adding more RAM can often restore features again which had mysteriously stopped working. (Lackey n.d.) References Betsa, F. (n.d.). 'Tweaking Windows XP.' YSU Help Desk (online). Available: http://helpdesk.ysu.edu/news/vol2.1/TweakingWindowsXP.htm (May 18, 2006) Bott, E., Siechert, C. Stinson, C. (2004). Microsoft Windows XP Inside Out, Second Edition. Microsoft Press; 20th Bk&Cr edition Laskin, I. (n.d.). 'Windows XP - Memory Lover! Windows XP proves you can never have too much memory.' Practicalpc.co.uk (online). Available: http://www.practicalpc.co.uk/computing/windows/ramneeds.htm (May 18, 2006) Nichol, A. (2006). 'Virtual Memory in Windows XP.' Aumha.org (online). Available: http://www.aumha.org/win5/a/xpvm.php (May 18, 2006) Rankin, B. (2005-2006). 'Make Windows XP Run Faster!' AskBobRankin.com (online). Available: http://www.askbobrankin.com/make_windows_xp_run_faster.html (May 18, 2006) Sechrest, S. and Fortin, M. (2001). 'Windows XP Performance.' Microsoft (online). Available: http://www.microsoft.com/technet/prodtechnol/winxppro/evaluate/xpperf.mspx (May 18, 2006) Read More