[A86] Re: ? [OT]

To: assembly-86@lists.ticalc.org
Subject: [A86] Re: ? [OT]
From: rabidcow@juno.com
Date: Tue, 6 Mar 2001 23:23:10 -0800
Reply-To: assembly-86@lists.ticalc.org

com files run in real mode or virtual 8086 mode.  The chip is purposely
imposing those limits because the program is designed for them. 
Protected mode does not have this limitation.  If you for some reasen
loaded a com file (or some other raw binary image) in protected mode,
you'd have 4 GB to play with.

1.5 GHz mac?  anyone?

ok, no fan is impressive.

The cpu would definitely generate less heat if it didn't have all the
extra transistors to support 8086 mode.  Whether or not that would let
you remove the fan, I don't know.

I remember a story from long ago (386 days?) when someone designed a pc
that had no fan, even in the power supply.  It was designed to use
convection to genereate airflow instead.  Customers wouldn't buy it.  Too
quiet!  No pleasing some people I guess. :)

-josh


On Wed, 7 Mar 2001 00:37:18 -0600 (CST) Shawn Ells <sells@inetnebr.com>
writes:
> 
> To your first remark: com files 64k max.
> And your fourth: If we have a Mac and a PC of equal clock speeds 
> (Mhz) for them 
> to do the same task the Mac will more offen than not compleat the 
> task first.
> 
> By the by, Macs (G3,G4,G4 Cube, IMac) don't have fans on there 
> cpu's, heck the 
> G4 Cube doesn't have any fan what so ever :-P lets see a PeeCee do 
> that. 
> 
> Quoting rabidcow@juno.com:
> 
> > 
> > what?
> > 
> > afaik, 32-bit protected mode has no memory restrictions related to 
> the
> > 8086.
> > There is a limit to a 4GB address range (per task), but that's 
> because
> > everything is limited to 32 bits.  Actually, I bet a really sneaky 
> os
> > could extend that using segment registers, but it wouldn't really 
> be
> > worth it.
> > 
> > Most of the 8086 instructions are still useful, defaulting to 32 
> bits
> > rather than 16.  The main problem with supporting them (besides 
> the extra
> > hardware to decode them, not a minor issue) is that they take up 
> some of
> > the shorter (8-bit) opcode values forcing newer instructions to be
> > longer.  Variable length instructions are generally a bad thing 
> anyway
> > for modern processors.
> > 
> > Have you seen anything about IA-64?  It has "modes" supporting 
> older
> > processors as intel has done in the past, but in the native ia64 
> mode,
> > older instructions *aren't* supported.  Instructions are packed 
> into
> > fixed length structures (up to 3 in each 128-bit "bundle"), 
> there's two
> > large register stacks, predicate registers for conditional 
> execution
> > (less cmp/jmp speedbumps).  It really seems optimized for c-like
> > languages.  They don't seem to have left themselves room to add 
> extra
> > features tho. (like MMX, SIMD, etc)
> > 
> > *sniff* and there's no rotate instruction!!
> > 
> > and to get *really* picky ;), "of equal speed" doesn't mean 
> anything.  I
> > could say they're "of equal speed" if the take the same amount of 
> time
> > for a given task.  Then, by definition, that Mac couldn't take less 
> time
> > if it's of equal speed.  You could say they're of equal speed if a 
> given
> > instruction takes the same amount of time.  Then it's a matter of 
> which
> > takes more instructions for the task.  You could say equal clock 
> speed,
> > then even previous generations of x86 chips would finish in less 
> time.  A
> > better measurement might be of equal cost or equal heat output.
> > 
> > -josh
> > 
> > 
> > On Tue, 6 Mar 2001 23:22:19 -0600 (CST) Shawn Ells 
> <sells@inetnebr.com>
> > writes:
> > > 
> > > In all accuality we really need to start over with compuers.
> > > The x86 still has the old 8086 op codes, and some of the memory 
> addr 
> > > restrictions. Thats why if a Mac and PC of equal speed are set 
> to do 
> > > the same 
> > > task that the Mac will get done first.
> > > 
> > ________________________________________________________________
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> 
> 
> 
> "I can't be wrong - my modem is error correcting."
> "Never underestmate the power of the off swich."
> "I plan on living for ever. So far so good."
> 
> 
> 
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