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View Full Version : What's different (aside from CPU), Mac vs PC?


AHunter3
06-18-2005, 03:29 PM
In a thread on another msg board about how come the MacOS, when ported to Intel, won't "just run" on any old standard-issue PC, I made the claim that the rest of the chips in the respective chipsets are also different, that a Mac with an Intel chip where the PPC chip currently resides does not a PC make. (And that therefore a Dell would be different hardware than a Mac with an Intel CPU).

I was asked to back that claim up with cites.

I can see three possibilities here:

a) I am wrong now and, in fact, such was never the case. In other words, a Mac Plus with an Intel 8088 substituted for the Motorola 68000 would boot MSDOS, and an IBM XT with a Motorola 68000 (plus an Apple Mac ROM, we stipulated that this old HW difference did indeed exist) would let you load System 3, no problemo; and that a Quadra with the '040 chip swapped out for a 486 would run Windows for Workgroups just as a Gateway 486-66 with an '040 (and a Mac ROM) would natively boot System 7.1. I'm pretty sure none of these things are true, and that the two hardware platforms were different all over the place and the operating systems would have definitely had to have been rewritten for the different architecture.

I should also stipulate here that when I say "swapped out" or "substituted for", I mean by the manufacturing plant, not by some guy with a soldering iron, i.e., we assume that they also change the pins and sockets and connectors that most directly feed into the CPU.

b) I was right with regards to these differences back in time as with the older models discussed above, but it isn't true any more due to some combination of hardware abstraction layers and convergence of actual parts used over the last decade. In other words, XP and OS X don't make direct calls to the actual hardware and therefore seldom care whether the memory management unit is of this architecture or that architecure, etc.; and furthermore the two platforms tend to use more of the same parts than they used to, e.g., NuBus giving way to PCI and that sort of thing to the point that yes, if, hypothetically speaking, Dell substituted a G5 chip for the Intel Pentium, a Dell should be able to boot OS X (even if you had to use something like XPostFacto to get it to install), and that therefore OS X ported to Intel really ought to run on any PC hardware except to the extent that Apple deliberately writes in little "check" routines to keep it from doing so, etc.

c) I'm still right, and OS X is no more capable of running on a hypothetical PowerPC Dell box than it is of running on a NuBus PowerMac 7100, because this and that chip that OS X expects to find on a Mac isn't present on an industry-standard PC without being specifically rewritten to accomodate that architecture.


Please let me know whatever you know on the subject, thanks.

giskard22
06-18-2005, 04:41 PM
I think the truth is somewhere between B and C. C would certainly have been true with Classic Mac OS. But Mac OS X has been simultaneously developed both for Wintel and PowerPC architectures, and builds of it that include the Wintel code are obviously capable of working on a standard Wintel computer. By all reports, that's pretty much what the development kits are that Apple is distributing (people have reported loading Windows XP on them with no problems).

Now, it's worth pointing out that we have no idea what a production Intel-based Mac is going to be like, and Apple said straight-out that measures would be taken to prevent Mac OS X from being loaded on a generic PC. But that doesn't mean it wouldn't work fine without the lockout mechanism in place. :)

mclbruce
06-18-2005, 05:49 PM
Interesting question. Macs have been getting more and more like PCs over the years. Here's a quick checklist:

Memory: same
Hard disks: physically the same, some differences in format. Can read and write each other's format with third party products.
USB: same
Firewire: same
PCI: physically the same but the same cards will not work. Windows and Mac have different firmware on their PCI cards. Some cards can have firmware flashed to work on one or the other.

In the past there was SCSI, ADB and AppleTalk/LocalTalk, SCSI, and NuBus for the Mac. SCSI was used on some PCs, but the rest was not. Apple is clearly making their products more and more like PCs physically.

The predecessor to OS X was NeXT's OS. It did "just run" on PCs. It was designed to do so. As giskard22 said I think we'll have to wait and see. To me Apple has a lot of choices here. I don't think they will put out a machine that's phyisically identical to a Dell, but I think they could do so with very little effort.

DavidRavenMoon
06-18-2005, 06:06 PM
The motherboards and related chip-sets are different. Also PCs use BIOS and Macs use OpenFirmware. The current MacIntel developer machine is a regular PC, but Apple says that the final Intel based Macs will not be the same.

Let's take the example of trying to run Windows on a G5. The reason you can't run Windows on a PPC Mac, for instance, is besides the OS needing to be recompiled for the CPU and bite order, is also that Windows knows nothing of the hardware it's running on, and has no drivers for that hardware. So it can't talk to the hard disk or memory controllers.

This is the same reason why OS X will not run on a 7100.

So even though the developer's copy of Tiger runs on a PC, the final Intel Macs will be quite different, in regards to the motherboards.

K1W1
06-18-2005, 06:41 PM
In the context of the thread you may find this interesting.

http://www.arn.idg.com.au/index.php/id;1711947473;fp;8;fpid;0

RacerX
06-18-2005, 10:56 PM
The predecessor to OS X was NeXT's OS. It did "just run" on PCs. It was designed to do so.
And the fact that it was designed to do so should not be under estimated in this case.

The fact that, say, OPENSTEP 4.2 runs just as well on a system made by IBM as one made by Dell or HP had little to do with the processor... it had to do with the fact that those companies were making Windows compatible hardware... which meant that they were compatible (to some degree) with each other.

But lets look at another example... using the same operating system: OPENSTEP 4.2.

OPENSTEP 4.2 runs great on NeXT hardware... of course, it was designed to.

NeXT hardware was based on Motorola's 68030 and 68040 processors. They had built in ethernet, SCSI and later models even used ADB (Apple Desktop Bus).

So if OPENSTEP 4.2 runs on a 68040 NeXT system (which uses much of the same hardware as an Apple Quadra) will it run on a 68040 Apple system?

No.

Processors, components, etc. are not the heart of a computer... the logic board to which all these parts and pieces are connected is vital to how the operating system works with the computer. Apple systems and NeXT systems may seem very much alike (specially if you are running down a check list of components), but they really aren't.

To date Apple has never made an Intel based system. Apple has no need to make their systems Windows compatible, so they are in no need of being compatible with any other PC maker's systems.

Odds are the new Intel based Macs are going to be unique to Apple... and the final version of Mac OS X for these systems is going to be designed to run on them.

We should not forget that the version that developers are using stems from the original Rhapsody for Intel release which was designed for PCs in general (although it only ran on a small subset of PC hardware). Apple has been continuing with this line without a hardware model other than, again, a limited subset of PC hardware.

Now that Apple is designing it's own Intel based hardware, they'll port this version of Mac OS X over to the finalized version of that hardware and that is what people will be getting in their systems.


As for the idea of running the developer version of Mac OS X on a standard PC, it should be noted that as this was a backup plan, the odds are very much against it having drivers for anything other than the exact hardware Apple is using in the development systems. Drivers were one of the biggest headaches with Rhapsody for Intel.

Markle
06-19-2005, 04:50 PM
Since this wasn't specifically mentioned in the reference to different motherboards and chip-sets, let me point out that Apple uses ROMs that aren't on generic PCs.

The boxes won't be as interchangeable as many people are hoping. Ultimately you may be able to buy a copy of Windows and run it on a Mac, giving you a dual-boot machine. But Windows is unlikely to run as fast on a Mac as on a dedicated Windows box because some of the inter-hardware communication may have to be emulated. Also, just because Apple will be using Intel chips, it doesn't mean they'll be the SAME Intel chips that Microsoft builds on. Time will tell.

Markle

NovaScotian
06-19-2005, 06:01 PM
While I agree that OS X is unlikely to run "out of the box" on a PC designed and configured to run WinXP "out of the box", I think that it will be possible to augment the system to make it do so unless there is some specific trick to prevent it, i.e. a "dongle" on the motherboard.

Remember that OS X was not supported on pre-G3 machines either but Ryan Rempel wrote XPostFacto to add the necessary kexts and helper code to make it possible. If you look at the XPF forums, you'll see that people are running Tiger on some pretty antique machines (a challenging hobby for most of them). Panther, for example, wasn't supposed to run on any USBless machine. That precluded the Beige G3, but I had only moderate difficulty getting 10.3 running on a Beige using XPF.

Don't you think there will be other Ryan Rempels out there?

hayne
06-19-2005, 06:38 PM
Don't you think there will be other Ryan Rempels out there?
Note that the OS X license says that you are only allowed to run it on Apple hardware.
Don't you think that Apple lawyers might have something to say if anyone published a recipe for violating this licence?

NovaScotian
06-19-2005, 07:30 PM
Note that the OS X license says that you are only allowed to run it on Apple hardware.
Don't you think that Apple lawyers might have something to say if anyone published a recipe for violating this licence?
That's a tough call, I think; along the same lines ISPs not being held responsible (so far) for porn or music swapping (or the phone company for obscene phone calls, for that matter). It's the person who installs the code and runs OS X on his Dell that is breaking the law in my view (but then I'm NOT a lawyer, though Ryan Rempel is).

RacerX
06-20-2005, 07:10 AM
Also, just because Apple will be using Intel chips, it doesn't mean they'll be the SAME Intel chips that Microsoft builds on. Time will tell.
I don't think that this point can be emphasized enough. Both the fact that they may not be using the same chips as what PC makers are using and that we are too early to really tell where Apple is going with this.

Apple has given themselves a year to develop new hardware. I would imagine that we'll all have a better idea when Apple releases the developer notes for that hardware, which I would guess would be around next spring to give third party hardware developers time to adapt.

"Time will tell" really sums all this up best at this point in the game.

chabig
06-20-2005, 07:18 AM
Also, just because Apple will be using Intel chips, it doesn't mean they'll be the SAME Intel chips that Microsoft builds on.
I think it's a safe bet that they will be exactly the same chips. That's why Apple's making the switch--because the CPUs are available in large quantities. During the keynote, Steve showed us OS X running on a Pentium 4. If Apple were going to use some custom chip, he could have just said the keynote was running on an Intel chip. Instead, we know it was a Pentium 4. We also know that Apple's machines will boot to Windows. Therefore, the CPU has to be industry standard.

Chris

hayne
06-20-2005, 10:24 AM
During the keynote, Steve showed us OS X running on a Pentium 4. If Apple were going to use some custom chip, he could have just said the keynote was running on an Intel chip. Instead, we know it was a Pentium 4. We also know that Apple's machines will boot to Windows.

You seem to be drawing conclusions about the future hardware based on facts about the machines used in a demo and those supplied to developers for initial development. That is not valid reasoning.

NovaScotian
06-20-2005, 10:38 AM
I'm getting out of my depth here, but I understand that a lot of what a CPU does is not hard-wired into the chip, it's microcoded and stored in non-volatile memory on the chip. I know, for example, that bad but critical bits and pieces are printed redundantly and the best one is chosen by inspection before shipping the chip.

If that's the case, then custom microcode can make the chip unique to Apple in any number of tricky ways, even though the circuitry is otherwise identical to a "PC" chip.

My vote here is this: If Apple wants a Dell to run OS X, it will; but if they don't it sure won't.

chabig
06-20-2005, 07:52 PM
You seem to be drawing conclusions about the future hardware based on facts about the machines used in a demo and those supplied to developers for initial development. That is not valid reasoning.
I am. But it's just a guess. Things may, of course, turn out differently.

Chris