Hi Rob!
02 Feb 2002, "Rob" <[EMAIL PROTECTED]> wrote:
R> This may be a naive question, but I'm curious.
R> Most of the limitations of DOS that I see, seem to be imposed upon it,
R> such as lack of further developement. It looks to me to be a concerted
R> effort to kill it. Is it dead due to inherent flaws in the system or
R> because the wealthiest man in the world, with extreme power and
R> influence over government, military, technological, and corporate
R> entities says it's dead?
The only thing bill gates is concerned about is money ...
He would not kill DOS, and spend Billions of $ to develope Win NT if he
could happily sell on DOS.
But he has the vision of a PC in _EVERY_ home (eg sell operating systems to
ALL world inhabitants) and he can _NEVER_ achieve this goal with DOS.
And yes ... there are immense flaws in the design of DOS.
It is designed for the 8086.
And for this computer it was great. (eg the 8086 was completely 16 bit, had
no MMU [memory management unit - needed for paging and virtual memory],
only real mode and only supported 1 MB of RAM directly.)
Than came the 286 ... supports more memory, and contains first
implementation of protected mode. (protects address space of different
processes, support for different priority processes [eg. kernel and
userspace])
Than the HUGE advance of the 386.
32 Bit extension, MMU, mature implementation of protected mode, 4 GB
addressable memory space.
The 386 offers extreme power, and DOS is not able to use it.
All later processors offered only speed improvements, but the 386 lay the
basic for modern OSes.
(486 integrated FPU and cache, and was slightly pipelined.
586 fully pipelined, and superscalar (can execute up to 2 commands per
clock.
686 integrated 2nd level cache on the die, speculative execution of up to 3
commands per clock.)
There are some tries to evade DOS defficiencies.
Eg XMS to address more memory.
This works so, that you load a driver in DOS, which switches to protected
mode (where you can address the RAM) and copies small parts to under 1 MB
if needed.
Naturally this is painfully slow (every mode switch is expensive, and the
copying of the data is also slow)
Eg 32 bit addressing.
DJGPP creates 32 bit protected mode executables - GREAT ....
_BUT_ DOS can't operate in Protected mode, so these programs have to switch
back to real mode, for every IO operation, and for every DOS service they
need. (read DJGPP faq Why are IO bound processes so slow)
[PS: this is the same solution as win9X ... switch to PM do your thing
there, and call dos functions in realmode if needed]
I like DOS also ... but with me this is because of nostalgy.
And to be honest now I would never use DOS on anything higher than a 486.
R> Rob:
CU, Ricsi
--
|~)o _ _o Richard Menedetter <[EMAIL PROTECTED]> {ICQ: 7659421} (PGP)
|~\|(__\| -=> Send more tourists ... the last ones were delicious! <=-
