windows/DOS question... 
Author Message
 windows/DOS question...

hey...what do they REALLY mean when they talk abt a 'dos-box'...and i've read a
couple times that windows actually 'sits' on top of DOS?? what does that mean?
is like hardware->kernel->DOS->windows? cos that would make windows too slow,
rite?

and the ms-dos prompt...does that actually give u access to the underlying DOS
os...or is it just a really good emulator for DOS thats included with
windows...

sorry if the questions sound stupid...im confused abt this...fanks!

--The Mosquito Scriptkiddiot.
"There are two sides to every story...and then there is what really happened."
;p



Tue, 28 Jun 2005 14:27:55 GMT  
 windows/DOS question...

| hey...what do they REALLY mean when they talk abt a 'dos-box'...and
| i've read a couple times that windows actually 'sits' on top of DOS??
| what does that mean? is like hardware->kernel->DOS->windows? cos that
| would make windows too slow, rite?
|
| and the ms-dos prompt...does that actually give u access to the
| underlying DOS os...or is it just a really good emulator for DOS
| thats included with windows...

Windows 95, 98 and Me look like this:

+--------------------+
|     DOS box        |
|  +--------------+  |
|  |    Windows   |  |
|  |  +-----------+--+
|  |  |   DOS, BIOS  |
+--+--+--------------+
|      Hardware      |
+--------------------+

This diagram shows that a DOS box relies partly on Windows, partly on the
underlying DOS machine, and partly on the hardware. Things like the screen
and file system are handled by Windows, although you can still access
certain hardware devices directly. A modern Window system will have
protected-mode drivers for most things, making it less necessary to keep a
copy of DOS underneath.

Windows NT, 2000 and XP look like this:

+-----------------+
|     DOS box     |
+-----------------+
|      Win32      |
+-----------------+
|      Kernel     |
+-----------------+
|     Hardware    |
+-----------------+

The DOS box relies on the Win32 API to provide everything; likewise, Win32
can't access the hardware without going through the kernel.

--
Tim Robinson, MVP (Windows SDK)
http://www.themobius.co.uk/



Sat, 02 Jul 2005 03:50:16 GMT  
 windows/DOS question...


[ ... ]

Quote:
> Windows NT, 2000 and XP look like this:

> +-----------------+
> |     DOS box     |
> +-----------------+
> |      Win32      |
> +-----------------+
> |      Kernel     |
> +-----------------+
> |     Hardware    |
> +-----------------+

> The DOS box relies on the Win32 API to provide everything; likewise, Win32
> can't access the hardware without going through the kernel.

A DOS box can bypass Win32 and go to the Kernel, via a virtual device
driver.

--
    Later,
    Jerry.

The universe is a figment of its own imagination.



Sat, 02 Jul 2005 04:39:51 GMT  
 windows/DOS question...
|| The DOS box relies on the Win32 API to provide everything; likewise,
|| Win32 can't access the hardware without going through the kernel.
|
| A DOS box can bypass Win32 and go to the Kernel, via a virtual device
| driver.

VDDs on NT are still just DLLs that get loaded into NTVDM. If you need to
write your own VDD, you're supposed to interact with your hardware through
normal Ioctls. I don't think there's any way of introducing some kernel-mode
code which will trap requests from DOS boxes directly.

--
Tim Robinson, MVP (Windows SDK)
http://www.themobius.co.uk/



Sat, 02 Jul 2005 04:53:13 GMT  
 windows/DOS question...


[ ... ]

Quote:
> VDDs on NT are still just DLLs that get loaded into NTVDM. If you need to
> write your own VDD, you're supposed to interact with your hardware through
> normal Ioctls. I don't think there's any way of introducing some kernel-mode
> code which will trap requests from DOS boxes directly.

They can do that too, but they also have access to a number of functions
that I don't believe are considered part of the Win32 API as such.  For
example, a VDD can use VDDQueryDMA and VDDSetDMA to directly request
DMA, instead of going through the Win32 API (where it would usually
involve something like CreateFile followed by a read or write).

--
    Later,
    Jerry.

The universe is a figment of its own imagination.



Sat, 02 Jul 2005 14:15:23 GMT  
 windows/DOS question...

Quote:


> || The DOS box relies on the Win32 API to provide everything; likewise,
> || Win32 can't access the hardware without going through the kernel.
> |
> | A DOS box can bypass Win32 and go to the Kernel, via a virtual device
> | driver.

> VDDs on NT are still just DLLs that get loaded into NTVDM. If you need to
> write your own VDD, you're supposed to interact with your hardware through
> normal Ioctls. I don't think there's any way of introducing some kernel-mode
> code which will trap requests from DOS boxes directly.

   There is a fairly trivial way - you can directly intercept #GP
entry in every processor's IDT and parse the faulting instruction
before NT's code. You would also have to implement your own spinlock.
A good question is not the mere possibility but the reason to do
things this way...

/BP



Sat, 02 Jul 2005 16:44:57 GMT  
 
 [ 6 post ] 

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