🚀 go-pugleaf

In article <38299@iuvax.cs.indiana.edu>, sl197009@silver.ucs.indiana.edu (Chima Echeruo) writes:
> 
> I have read many "experts" saying that the 286 is far slower than a 386.
> ... won't a 25Mhz 286 outperform an equivalent 386 while in real mode?

    From what I've seen, a 16MHz 286 runs DOS code at about the same speed
as a 16MHz 386SX, +/- 5% or so.  The instruction timings are about the same,
and the bus widths are both 16 bits.  A 16MHz 386 should be consistently
faster, even running 16-bit code and without a RAM cache.  The reason is that
even if nothing else uses the 32-bit bus bandwidth, the instruction prefetch
unit on the 386 always loads whole doublewords.  I think the effect of this
is something like a 20% improvement in speed over a same-speed 286.  The 286
also does not support memory interleaving systems, so for >16MHz, you will
be forced to have wait states on main memory.  A 20MHz 386 can still work at
"near 0 wait states" with interleaved memory.  At higher speeds, a static
RAM cache is necessary for avoiding wait states.  I don't know if there are
cache controllers for the 286, but I'm pretty sure the Intel cache controller
only works with 386's.
> 
> I do not think that the 286 is dead, maybe it is not the state-of-the-art in
> computer technology but it provides a very *fast* system for the average
> computer user. If the SX does not go past 16Mhz, I do not see the benefit for
> upgrading to a 386sx.
> 
    I agree that fast 286's are perfectly good machines for running almost all
DOS applications, and are guaranteed to have a high level of support for many
years due to the huge number of systems around.  As a sort of souped-up 8086,
I think it still has a very legitimate market.  I think that the 386SX puts
a LOT of pressure on new fast 286's (say 16MHz or higher), because the price
differential is quite small, both will run DOS code about equally well, but
the 386SX offers a bit more.  If I had a fast 286 machine, it certainly
would not be worth it to me to "upgrade" to a 386SX, but I wouldn't buy
another 286.
    By the way, Intel has already announced the 20MHz 386SX, and a version of
their cache controller for the SX.  A 20MHz 386SX with memory interleaving or
a cache would be significantly faster than a 20MHz 286 with the unavoidable
wait states.

 -David Hinds
  dhinds@popserver.stanford.edu