Information Technology Reference
In-Depth Information
However, Table 31 can give some idea of how the size of pro
grams increases over time.
The third reason mentioned earlier, that the speed of software
is sacrificed when a computer has only the minimum amount of
memory needed, is connected to the need to move materials be
tween virtual memory (on a disk) and main memory. Disk access
requires the physical movement of disks and read/write heads, so
large amounts of data transfer can take a long time. Ideally, one
would like material to flow from virtual memory to main memory
just once—when the program section or data are first needed.
However, if main memory is too small, then current sections may
continually replace previous ones. The result can be constant move
ment of materials between disk and main memory—a situation
sometimes called
thrashing
. On personal machines, one sometimes
can hear constant disk activity, well beyond the loading of initial
materials. When this circumstance arises, a larger memory often
can make a substantial difference. With more memory available,
more of a program and its data can reside in memory before a new
request for information from virtual memory requires something to
be replaced. When performance seems particularly slow, a com
puter owner may want to investigate whether the addition of main
Table 3-3 Growth in the Size of an Operating System over Time
Date
Product
Approximate Length
August 1981
MSDOS
4000 lines of (assembly
language) code
March 1983
MSDOS 2.0
20,000 lines of code
August 1993
Windows NT 3.1
6,000,000 lines of code
September 1994
Windows NT 3.5
9,000,000 lines of code
August 1996
Windows NT 4.0
16,000,000 lines of code
February 2000
Windows 2000
18,000,000 lines of code
2000
Windows NT 5.0
20,000,000-29,000,000
lines of code (depend
ing on source used)
2001
Windows 2000
35,000,000 lines of
code
2002
Windows XP
40,000,000 lines of
code
