From: John Beckett 

"Geo"  wrote in message
news::
> Poking the number into screen memory instead of using a display function is
> much faster.

I never never found out exactly how the Windows NT family handles this, but
it is a lot less useful than was the case when we played with DOS.

A 16-bit program would often access the COM1 serial port by performing i/o
with the 3F8h ports. Such programs often run successfully under NT, but the
i/o instructions cause a hardware interrupt and are emulated by the
operating system. So, a single 'in' instruction to read a byte from COM1
might end up executing 1000 instructions in the OS.

If a 16-bit program stores data in the screen memory while running in a
window on the screen, it is obvious that the same hardware interrupt and
operating sysem emulation is taking place.

If a 16-bt program is running in full-screen mode, I suspect some tricky
memory mapping is allowing the program direct access to screen memory (no
emulation). I don't think you can use VC6 to write such a program.

At any rate, worrying about these low-level details is not a good way to
learn any high-level language.

John

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