Page 105 - DCAP408_WEB_PROGRAMMING

Unit 6: Memory Management (II)

applications simultaneously, etc., you may get away with it. Sooner or later, though, it will Notes
become a problem.
Now we’ve defined the problem. What is the solution? If you build up software, web sites , or
graphics (by means of high end software), the answer, even though you may not like it, is to
advance the operating system. The WindowsNT memory model is the answer. WindowsNT,
Windows2000 and WindowsXP share a hugely different memory model. Under this NT based
memory management system, resources are not restricted. As long as you have sufficient physical
memory (RAM) or virtual memory (disk space) your applications will not run out of resources.
The WindowsNT memory system assigns resources dynamically. As long as the memory is
obtainable, your application can have it.
Even better, every application obtains its own virtual copy of the operating system. That means
that, applications are isolated and, if an error appears, system memory is not corrupted. When
an application terminates, all the memory assigned to it is released back to the operating
system. That means that resource, or memory leakage is also almost nonexistent. It is likely for
an application to incessantly demand more and more memory and the system will provide it,
until memory turns out to be short, but closing the application releases all that memory without
the requirement to reboot the machine.
The following chart displays the memory assigned for each particular purpose by the various
operating systems:

6.3.2 Resource Comparison

Window/Menu Handles about 200 32KB (each) Unlimited
Timers 32 Unlimited Unlimited
COM/LPT ports 4 each Unlimited Unlimited
Listbox items (per listbox) 8KB 32KB Unlimited
Listbox data (per listbox) 64KB Unlimited Unlimited
Edit control data (per control) 64KB Unlimited Unlimited
Regions All in 64KB segment Unlimited Unlimited
Logical pens, brushes All in 64KB segment 64KB segment Unlimited
Physical pens, brushes All in 64KB segment Unlimited Unlimited
Logical fonts All in 64KB segment 750-800 Unlimited
Installed fonts 250-300 (best case) 1000 Unlimited
Device Contexts 200 (best case) 16KB Unlimited

While Windows95, Windows98 and WindowsMe operating systems enhanced memory
management enormously over Windows 3.1, they were still intended for the home user. They
were never proposed to be a severe development platform. Coming across errors is a part of
software development. An operating system that is not fault tolerant has no place in the software
development environment. If you develop software, or web sites by means of a serious
development tool, you should be using WindowsNT, Windows2000, or WindowsXP.

Task Illustrate the function of User resources.

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