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Certification : Operating Systems
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220-901 and A+™ Practical Application
Usually, a computer memory consists of a physical RAM
memory, and virtual memory. The physical memory is expensive, and limited in
size. The virtual memory, on the other hand is cheap, and implemented using
the computer's mass storage (such as hard disk drive).
computer appears to the programmer to have its address space limited only by
the addressing range, not by the amount of memory which is physically
connected to the computer as main memory. Of course, the virtual addresses
needs to be translated to physical addresses for actually executing the
instructions. This is done by virtual address translation.
example, a 32 bit CPU can address 4GB of address space. This is usually more
than the physical RAM available in a computer. Virtual memory enables the
processor to access all 4GB of the address space as if it were available
physically. The processor translates (‘maps’) the virtual addresses from
an instruction into the correct physical equivalents on the fly as the
instruction is executed. The processor manages the mapping in terms of pages
of 4 Kilobytes each.
Only the parts of the program and data
that are currently being in use are held in physical RAM. Other parts are held
in a swap file (Windows 95/98/ME: Win386.swp) or page file (in 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, in turn retrieve the 4 KB page containing the address from the page
You can set the place, and size of the page file. To set it, by going to
Control Panel | System | Advanced tag. Checkout for “Performance” Section,
and set the required values. Note that it may be better to leave it at default
values. If you have large hard disk, set the page file big enough, may be as
high as 700-800MB. There is no harm if the page file is set to a large value.
A small value for page file may slow down the performance.
Disk Defragmentation is the process of reorganizing a hard
disk drive's data so that the data is retrieved from the hard disk
efficiently. Over a period of time, the files in the hard disk are severely
fragmented, and take a lot of time to load. Disk defragmentation is required
from time to time, particularly on heavily used machines.
On WIndows 2000 machine, Disk Defragmenter can be opened a number of
different ways. The most common methods are listed below.
* Start | All Programs | Accessories | System Tools | Disk Defragmenter
* Start | Run | and type dfrg.msc in the Open line. Click OK
* Start | Administrative Tools | Computer Management. Expand Storage and
select Disk Defragmenter
A buffer is used to temporarily store information while the information is
being processed. A file usually refers to a permanent store of code or data.
Usually, when you are working on a file, a buffer is created. The buffer is
written to the file when you save the file.
Cache is a high-speed access area that can be either a
reserved section of main memory or a storage device. Different types of
caches include L1 cache, and L2 cache. L1 cache is usually internal to
the processor. L2 cache is usually external to the processor. These
caches sit between the CPU and the DRAM (Main memory). Like L1 caches, L2
caches are composed of SRAM but they are much larger.
Several applications may generate temporary files when you
are working on them, or browsing the Internet. Over a period of time, these
files may occupy sizeable amount of hard disk space. It is necessary that
you cleanup the temporary files from time to time. For Windows 2000/XP, you
can delete these files by going to Start -> Programs -> Accessories
-> System Tools, and then selecting Disk Cleanup.
As seen in the above screenshot, you can delete files in
Recycle Bin, Catalog files etc. after reviewing the same.
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