What is the difference between a Dec Alpha and a Mac Power PC chip?

What is the difference between a Dec Alpha and a Mac Power PC chip?

Post by Michael neufe » Wed, 11 Jun 1997 04:00:00




> Hi to all,

> can some one please tell me what the difference is between an Dec Alpha
> and a Mac Power PC chip ?

> They are both RISC based processors right?

The DEC alpha and the Motorola/IBM/Apple PowerPC are both RISC chips.
Other than that, they have different instruction sets and therefore
aren't compatible with each other.

Quote:> Given stuff I have read about the Alpha one might conclude that if you
> can run Windows NT on an Alpha Work station then you should be able to
> do the same on a Mac Workstation right?

You can't run Windows NT natively on a Power Macintosh for two reasons:

1.      Microsoft no longer supports a version of Windows NT for the
PowerPC processor.

2.      Macs have traditionally been big endian machines, while Intel
based computers are little-endian. (This has to do with the order in
which the least significant and most significant bytes are dealt with.
On big endian systems, the most significant byte comes first and the
least significant comes last. It's the opposite on little endian
machines.) Both the PowerPC and DEC alpha support either big or little
endian mode, but Power Macs are hardwired inside so that they only
support big endian mode. This is why Power Macs can't run the PowerPC
version of Windows NT. Most non-mac PowerPC workstations can be switched
between big and little endian mode, so they can run the discontinued
PowerPC version of Windows NT.

Emulators such as Virtual PC emulate a Pentium processor on a Power Mac
and therefore allow the 80x86 version of Win NT to run.

 
 
 

What is the difference between a Dec Alpha and a Mac Power PC chip?

Post by Michael Nielse » Thu, 12 Jun 1997 04:00:00



> Hi to all,

> can some one please tell me what the difference is between an Dec Alpha
> and a Mac Power PC chip ?

> They are both RISC based processors right?

Hmm let's see, what is the differences between an amiga and a Machintosh
(the 680x0 series), and an intel machine, they are all cisc right ???

        Yeah right to some small extent, the best comparison is the Amiga
and the Machintosh in this case as they have the same kind of processor,
which makes them assembly compatible to an extent, however the hardware
archtecture is sufficently different that you cannot rum amiga os on
a MAC, or macOS on an amiga (without emulation), in the case of intel
and the amiga(or mac), there are significant differences, that is the
instruction set of the assembly is like day and night, there are not
many similarities, thus they are not any where near assembly compatible
and the Intel chip is Little endian (little end first, ie two thousand
and ten hex 0x2010 is enfact 0x1020) and the 680x0 series is big endian
that is
two thousand and ten is 0x2010.

Quote:

> Given stuff I have read about the Alpha one might conclude that if you
> can run Windows NT on an Alpha Work station then you should be able to
> do the same on a Mac Workstation right?

> If so why all the need for this emulaion and 3rd party board *to do
> windows on the Mac ?

> Some one also commented regarding the above that IBM and Microsoft
> recently had Windows NT running on a Mac and pulled it.

The problem with running NT on the PowerPC is just that the HAL
(hardware abstraction layer) has to be specifically written to work on
the particular architecture, microsoft is sure that NT it self will be
able to be compiled on any platform, as long as the HAL is in place.  

The HAL is what makes NT portable,  It is basicaly the emulation that
you are talking about..   I recently heard that CHRP group wanted NT
ported to the CHRP platform, and MS requested some thing like 600
million dollars for the project.  

Personally I don't think it is worth the hassel, having NT on a platform
is not that much better (worse in some aspects) than using linux, the
system administration interface of linux is getting very good, though of
course you may have problems building the kernel,  but since most
applications on linux are source distributed, they can be recompiled to
run on any platform where linux is installed.  All NT software is binary
distributed, so this does not apply, so unless the software companies
recompile the code on an PowerPC NT machine the software base won't be
there even with NT.

Of course you should use IMNSHO where ever applicable, and take into
account that the information I'm giving here is in part based on
information from the web which may or may not be factual.

In my personal opinion, I think it will be good for a platform not to
have the microsoft * hold on it, that way we will see some new
innovative software designs, and smaller companies will be able to
compete again (for a while).

        have fun
                mike

--
------------------------------------------------------------------------------
 Michael Nielsen        Telf: +45 4284 8433 x 360          

                        Fax:  +45 4284 5220
------------------------------------------------------------------------------
(my opionins in no way reflect those of my employer)
             At arbejede er godt, s? l?nge man husker at leve!
             (To work is good as long as we remember to live!)

 
 
 

What is the difference between a Dec Alpha and a Mac Power PC chip?

Post by Ken Walt » Thu, 12 Jun 1997 04:00:00



Quote:(Anthony) writes:

 Hi to all,

 can some one please tell me what the difference is between an Dec Alpha
 and a Mac Power PC chip ?

 They are both RISC based processors right?

 Given stuff I have read about the Alpha one might conclude that if you
 can run Windows NT on an Alpha Work station then you should be able to
 do the same on a Mac Workstation right?

NT was ported by DEC to the ALPHA and to run Intel Windows apps they
use a fairly good emulator.  The same would need to be done for the powerPC.

 If so why all the need for this emulaion and 3rd party board *to do
 windows on the Mac ?

The three machines have different instruction sets and architectures.

[...]

Ken Walter     (Remove antispam. from address)
All the above is hearsay and the opinion of no one in particular.

 
 
 

What is the difference between a Dec Alpha and a Mac Power PC chip?

Post by Rob Barr » Thu, 12 Jun 1997 04:00:00




> You can't run Windows NT natively on a Power Macintosh for two reasons:

> 1.      Microsoft no longer supports a version of Windows NT for the
> PowerPC processor.

True.

Quote:

> 2.      Macs have traditionally been big endian machines, while Intel
> based computers are little-endian. (This has to do with the order in
> which the least significant and most significant bytes are dealt with.
> On big endian systems, the most significant byte comes first and the
> least significant comes last. It's the opposite on little endian
> machines.) Both the PowerPC and DEC alpha support either big or little
> endian mode, but Power Macs are hardwired inside so that they only
> support big endian mode. This is why Power Macs can't run the PowerPC
> version of Windows NT. Most non-mac PowerPC workstations can be switched
> between big and little endian mode, so they can run the discontinued
> PowerPC version of Windows NT.

   This is not accurate.  The fact that MkLinux can run on an original
Power Mac in little endian mode indicates otherwise.  Any Mac can switch
its CPU into little endian mode; really the issue is OS availability and
getting the drivers written.  I don't believe the pre-PCI PowerMacs were
ever documented to the level that would make an NT port possible (although
the freely available MkLinux source code probably provides some good
hints).

   Something interesting about PCI PowerMacs, any PCI peripherals have
their control registers mapped as little-endian (even when the machine is
in big endian mode); this makes assimilation of PC-space PCI peripherals
easier. I believe the peripheral registers on the first-generation
PowerMacs were big endian however.
   (It shouldn't matter too much to a driver writer working in assembler as
the PPC has load and store-swapped instructions that make it easy to deal
with data or registers of either endianness no matter which mode you're
in).


   * Opinions expressed not necessarily those of my employer *

 
 
 

What is the difference between a Dec Alpha and a Mac Power PC chip?

Post by Andrew Klossn » Thu, 12 Jun 1997 04:00:00


Quote:> Power Macs are hardwired inside so that they only support big endian
> mode.

How would you do that?  The endian control is in the LE and ILE bits
in the CPU's MSR register, which cannot be "hardwired".


 
 
 

What is the difference between a Dec Alpha and a Mac Power PC chip?

Post by John W. Blackbur » Fri, 13 Jun 1997 04:00:00



:> Power Macs are hardwired inside so that they only support big endian
:> mode.
:
:How would you do that?  The endian control is in the LE and ILE bits
:in the CPU's MSR register, which cannot be "hardwired".

Also the PCI-processor bus chip (e.g. Bandit in the 7500/8500, PSX in the
6400) does automatic big-endian <-> little-endian traslation between PCI
cards and the processor/main memory.

John

--
John Blackburne; programmer, writer, consultant, trainer
tel/fax: Hong Kong (+852) 2816 7484
home page: <http://www.hk.super.net/~johnb>

 
 
 

What is the difference between a Dec Alpha and a Mac Power PC chip?

Post by Andrew Klossn » Fri, 13 Jun 1997 04:00:00


Regarding the PCI bridge performing endianness swizzling:

Quote:> (It shouldn't matter too much to a driver writer working in assembler as
> the PPC has load and store-swapped instructions that make it easy to deal
> with data or registers of either endianness no matter which mode you're
> in).

That's fine for programmed I/O, but inadequate when a PCI device DMAs
large buffers to memory.  You want those buffers to be filled in the
appropriate byte order.

I'm working on a controller board with a PLX 9060ES.  (It was designed
for the i960, so takes some serious glue to make to a 603E.)  It's
flexible enough that I can configure it to swizzle DMA but not
programmed register access.


 
 
 

What is the difference between a Dec Alpha and a Mac Power PC chip?

Post by Mike Meissne » Fri, 13 Jun 1997 04:00:00



>    This is not accurate.  The fact that MkLinux can run on an original
> Power Mac in little endian mode indicates otherwise.

Wrong.  MkLinux runs in big endian mode.

--
Michael Meissner, Cygnus Solutions (East Coast)
4th floor, 955 Massachusetts Avenue, Cambridge, MA 02139, USA

 
 
 

What is the difference between a Dec Alpha and a Mac Power PC chip?

Post by Rob Barr » Fri, 13 Jun 1997 04:00:00





> >    This is not accurate.  The fact that MkLinux can run on an original
> > Power Mac in little endian mode indicates otherwise.

> Wrong.  MkLinux runs in big endian mode.

   My mistake. Is it true of PMAC-Linux or Linux-PPC? If so maybe that's
what I was thinking of.

   Klossner's comment about the endian control bit not being hardwired,
still leads me to believe there is no reason why a PowerMac could not run a
little endian OS.


   * Opinions expressed not necessarily those of my employer *

 
 
 

What is the difference between a Dec Alpha and a Mac Power PC chip?

Post by Mike Meissne » Sat, 14 Jun 1997 04:00:00






> > >    This is not accurate.  The fact that MkLinux can run on an original
> > > Power Mac in little endian mode indicates otherwise.

> > Wrong.  MkLinux runs in big endian mode.

>    My mistake. Is it true of PMAC-Linux or Linux-PPC? If so maybe that's
> what I was thinking of.

All versions of Linux running on PowerPC hardware are big endian (the user
level stuff is the same, only the kernel/boot procedures are different).  In
fact, the only little endian OSes that I'm aware of (Windows NT and Solaris,
possibly PPC OS/2 but I'm not sure of its endian orientation) have been
withdrawn by their owners from the market after their initial release.

Quote:>    Klossner's comment about the endian control bit not being hardwired,
> still leads me to believe there is no reason why a PowerMac could not run a
> little endian OS.

I believe the endianess is wired in the boot logic and support chips, not in
the powerpc itself.  Note, the early Pmacs that were 601 based might have
additional problems, since the 601 little endian bit was non-standard.

--
Michael Meissner, Cygnus Solutions (East Coast)
4th floor, 955 Massachusetts Avenue, Cambridge, MA 02139, USA

 
 
 

What is the difference between a Dec Alpha and a Mac Power PC chip?

Post by Anil Thomas Maliyekk » Sat, 14 Jun 1997 04:00:00


: All versions of Linux running on PowerPC hardware are big endian (the user
: level stuff is the same, only the kernel/boot procedures are different).  In
: fact, the only little endian OSes that I'm aware of (Windows NT and Solaris,
: possibly PPC OS/2 but I'm not sure of its endian orientation) have been
: withdrawn by their owners from the market after their initial release.

: --
: Michael Meissner, Cygnus Solutions (East Coast)
: 4th floor, 955 Massachusetts Avenue, Cambridge, MA 02139, USA

Solaris isn't little endian.  It is endian independent.  SPARC Solaris
is definitely big endian, and x86 Solaris is little endian.  PPC
Solaris was probably big endian, as it makes no sense for it to run
in little endian mode when there is a slight penalty, and when
Sun is big endian biased anyway.

The PPC OS/2 that was originally based on the IBM MK 1.0 was little
endian.  If they do release a PPC OS/2 next year based on MK 2.0 or
a new monolithic kernel, I would be suprised
if it wasn't switched to big endian, especially if they want to add
UNIX 95 support and AIX compatibility.

 
 
 

What is the difference between a Dec Alpha and a Mac Power PC chip?

Post by Michael Meissne » Sun, 15 Jun 1997 04:00:00



Quote:> Solaris isn't little endian.  It is endian independent.  SPARC Solaris
> is definitely big endian, and x86 Solaris is little endian.  PPC
> Solaris was probably big endian, as it makes no sense for it to run
> in little endian mode when there is a slight penalty, and when
> Sun is big endian biased anyway.

I'm sorry to be such a pedant, but you obviously have never used PPC Solaris.
I have used PPC Solaris, and even ported GCC to it (my Solaris machine is now
running Linux).  It was definately little endian, and it chose little endian
over big endian because NT was little endian, and people in the industry
thought NT would wipe out all other systems.

Quote:> The PPC OS/2 that was originally based on the IBM MK 1.0 was little
> endian.  If they do release a PPC OS/2 next year based on MK 2.0 or
> a new monolithic kernel, I would be suprised
> if it wasn't switched to big endian, especially if they want to add
> UNIX 95 support and AIX compatibility.

--
Michael Meissner, Cygnus Solutions (East Coast)
4th floor, 955 Massachusetts Avenue, Cambridge, MA 02139, USA

 
 
 

What is the difference between a Dec Alpha and a Mac Power PC chip?

Post by Anil Thomas Maliyekk » Sun, 15 Jun 1997 04:00:00



: > Solaris isn't little endian.  It is endian independent.  SPARC Solaris
: > is definitely big endian, and x86 Solaris is little endian.  PPC
: > Solaris was probably big endian, as it makes no sense for it to run
: > in little endian mode when there is a slight penalty, and when
: > Sun is big endian biased anyway.

: I'm sorry to be such a pedant, but you obviously have never used PPC Solaris.
: I have used PPC Solaris, and even ported GCC to it (my Solaris machine is now
: running Linux).  It was definately little endian, and it chose little endian
: over big endian because NT was little endian, and people in the industry
: thought NT would wipe out all other systems.

I don't understand why they chose this.  It sounds completely unlike
Sun to make PPC Solaris little endian just because NT is little endian.
Especially considering that the AIX is big endian, and that by making
Solaris little endian on PPC, you would pretty much make it impossible
to access the base of AIX applications through binary compatibility.

Perhaps that is another reason why they killed Solaris off.  Because
they made stupid decisions in porting it.

 
 
 

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