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Up to a point, adding RAM (random access memory) will
normally cause your computer to feel faster on certain types of
operations. RAM is important because of an operating system component
called the virtual memory manager (VMM).
When you run a program such as a word processor or an Internet browser,
the microprocessor in your computer pulls the executable file off
the hard disk and loads it into RAM. In the case of a big program
like Microsoft Word or Excel, the EXE consumes about 5 megabytes.
The microprocessor also pulls in a number of shared DLLs (dynamic
link libraries) -- shared pieces of code used by multiple applications.
The DLLs might total 20 or 30 megabytes. Then the microprocessor loads
in the data files you want to look at, which might total several megabytes
if you are looking at several documents or browsing a page with a
lot of graphics. So a normal application needs between 10 and 30 megabytes
of RAM space to run. On my machine, at any given time I might have
the following applications running:
A word processor
A spreadsheet
A DOS prompt
An e-mail
program
A drawing
program
Three or
four browser windows
A fax program
A Telnet session
Besides all of those applications, the operating system itself
is taking up a good bit of space. Those programs together might
need 100 to 150 megabytes of RAM, but my computer only has 64 megabytes
of RAM installed.
The extra space is created by the virtual memory manager. The VMM
looks at RAM and finds sections of RAM that are not currently needed.
It puts these sections of RAM in a place called the swap file on
the hard disk. For example, even though I have my e-mail program
open, I haven't looked at e-mail in the last 45 minutes. So the
VMM moves all of the bytes making up the e-mail program's EXE, DLLs
and data out to the hard disk. That is called swapping out the program.
The next time I click on the e-mail program, the VMM will swap in
all of its bytes from the hard disk, and probably swap something
else out in the process. Because the hard disk is slow relative
to RAM, the act of swapping things in and out causes a noticeable
delay.
If you have a very small amount of RAM (say, 16 megabytes), then
the VMM is always swapping things in and out to get anything done.
In that case, your computer feels like it is crawling. As you add
more RAM, you get to a point where you only notice the swapping
when you load a new program or change windows. If you were to put
256 megabytes of RAM in your computer, the VMM would have plenty
of room and you would never see it swapping anything. That is as
fast as things get. If you then added more RAM, it would have no
effect.
Some applications (things like Photoshop, many compilers, most film
editing and animation packages) need tons of RAM to do their job.
If you run them on a machine with too little RAM, they swap constantly
and run very slowly. You can get a huge speed boost by adding enough
RAM to eliminate the swapping. Programs like these may run 10 to 50
times faster once they have enough RAM!
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