First post here, so let me introduce a bit: I'm a developer, mostly C++ for various OS (Unix, Linux, Apple, Windows - whatever, often cross platform) - been at it for over 25 years.
That said, I'll risk a bit of a rant on this topic. So many posts, it's tough to read the entire thread when you're busy - and I type fast, and since I know my stuff, I tend to expound.
When the choice to base OS X on Unix was made, there is now doubt that among many fine lines of reasoning, portability was at least one main point. The Unix inside OS X opened up options, and options is what Jobs must have considered, even 5 or 6 years ago.
I've skimmed past a bunch of Intel negative posts here, and most nod a postive thought toward AMD by comparison, but the PowerPC chip, as monsterously wonderful as the design is (even the earlier versions), the implementation of that design never really delivered as much benefit as it seemed it should. I remember my first look at the assembler potential; all those registers, all that power, and yet - so many obsticles remained in the way toward really significant performance dividends.
Like all comparisons of performance between chips, there are things the PowerPC does better than P4, and there are things the P4 does better than the PowerPC. AMD jumps in with some serious advantages over both, with yet another set of roadblocks that keep them from overpowering either of these by generous factors in all regards. In other words, it's like comparing three engines, each with 400, 410 and 425 horsepower, different ranges of torque and efficiency. They're all capable; what translates into results depends on implementation, like the weight of the final vehicle, the stability of the thing where the rubber hits the road - even the impact of air over the contour of the outer skin.
Don't kid yourself into thinking OS X is superior in all manners here. There's LOTS going for it, but for one, the thread implementations suck a huge power drain out of it when aimed at server applications (see Anandtech's review for info on this point).
Now, the Unix interior of the OS was the best possible choice Jobs and Co could have made, in my opinion. No other core has the track record for solidity and performance. They instantly inherited years of superiority over Windows. They still have some work to do, though - plenty of room for improvement even if they stopped advancement the GUI.
The implication of the x86 in all this is nearly meaningless. Jobs demonstrated an OSX x86 at the presentation Monday, and intimated that x86 builds have been made all along. As a developer of cross platform code myself, I can assure you that many if not most of the best Apple applications will port to x86 without much hassle or impact.
As to the notion that floating point comparisons between PowerPC and P4 are of some concern, well - there's two points on that. First, SSE2 does use non-standard floating point rounding logic - it's been an issue for some rare applications before. In some cases, especially 3d rendering, but perhaps some Photoshop, an SSE2 optimized version can produce slightly different results. This isn't very noticable in single images, but in a rendering of 3d animation, it can make for some very odd results where particle systems don't "match up" between frames. One most have an "all SSE2" or "no SSE2" rendering farm to make things mate just right.
However, beyond that point, there's little impact other than speed. Speed, of course, is of considerable issue, but to that end I doubt Intel will sit idle. They have plenty of room for improvement, and compilers are generally at the heart of using chip features. In rare cases, optimized assembler may be have been used on PowerPC applications, but even that is localized in competent development work, such that keeping it updated isn't a huge task.
It was reported that Mathmatica ported without effort. I'll bet $50 Photoshop is already set. I can't imagine Jobs would have left out portability consideration for all internal Apple products on OS X.
I seriously expect that anyone purchasing an x86 based Mac will, especially by the time one is available, hardly notice anything has changed.
Much has been made about device drivers, but I don't expect this will pose nearly the challenge that moving from OS9 to OSX posed. There may be occasional 'endian' issues in some cases, but for the most part the CPU is not going to be the central problem, unless the driver is entirely or largely written in assembler (something often avoided in Unix systems).
Anyway - no matter what you may have thought about the PowerPC, it's just a bunch of switches, and so is the P4. It's never been the sacred heart of anything. That has always been the OS, the applications and the standards of metaphores in the user interface. The chip has been all but irrelavent all that time. If that were not true, Mac wouldn't have continued to be Mac as the chips transformed one to the next.
Every part of the "personality" of the operating systems, be it Unix, Windows, Mac or other, has little or nothing to do with the CPU executing it. Even the viruses that currently attack the operating system, though somewhat more intimately tied to the CPU's own language and method of operation, direct most of their attention to the OS or an application running within it.
Likewise, the range of applications which give the Mac platform guts is entirely dependent on designs which have much more to do with the minds of the people who make them, than with the language of the CPU.
So, too, it is with the hardware overall. The CPU demands certain things of it's support chips, of course, but the character of the hardware - it's options, it's support for various standards, buses, memory - are all the result of designers taking advantage of options open to them, and choosing compromises in favor of one thing or another. While the CPU and it's supporting chipset provide you with options for PCIe or AGP, built in Firewire or USB, IDE, SATA or SCSI, it is the designer's choices that put those things there, aimed at pricing some product toward low end, medium, high end, workstations, servers or whatever. In this manner, Apple will remain Apple - and true to form, you'll get exactly what you've expected from previous offerings; tight integration of those components way over and above what the standard Wintel platforms have offered - all chosen as compromises among the various options available to them from the P4's various chipsets and standards (including what Apple may have designed themselves), and implemented according the personality of the guiding hands at Apple.
There will be nothing "Windows" like about an x86 Apple, unless you boot Windows on the machine. Of that I'm absolutely certain, unless of course Jobs dies or leaves the company before it's all implemented.
Then....what happens if P4's future plans don't quite live up to Jobs expectations? Consider the shudder going through Intel execs to read the headline "Apple considers AMD." Even if the volume doesn't warrant it, the promotional aspect of Apple x86 will have them flogging the engineers day and night to keep that from happening. And what does that mean? The motivation for competition against AMD will be stronger than ever, and AMD's reply will be stronger than ever. Considering the recent history in that regard, this is great news for everyone.
We will, one day, not too far off I think, have the delightful option of considering a 64 core workstation. Our choice will hinge on "Apple or Non-Apple" versions, depending on whether or not we want the OS X. It's up to Apple and it's public as to just how popular the "Apple" option will become to consumers.
...and now a word about misc. things I noticed on the way to page 90....
Shared video memory is a "low end" design option you'll probably NEVER see in an Apple. It's just not in Job's personality to cripple the graphics.
Despite words to the contrary, Windows 2000 and Windows XP can be stable running platforms. The interior of the operating system is uglier than my 4th grade teacher (which is saying something). However, my own dual AMD XP box runs for weeks - as in months - without crashing or encountering problems. I am, however, a knowledgeable user - and I keep it running that way by updating AVG, Adaware, and avoiding stupid mistakes which I know well from years of experience. Most users don't have that knowledge, and so their machines are riddled with nonsense that cripple and crashes their machines. It's not that I care to defend Windows - I'd rather use Unix, a long time preference of mine that dates back to 1979 for me. As a developer, though, I can't argue with 90%+ client base - so I have Windows in various flavors for testing and debugging....and, I simply don't want an errant assumption to go on without some minor correction - it's not inherent that Windows XP must be unstable; it's just not as simple to keep it that way for novice level users than it is on an Apple (which is, obviously, a plus for the Apple). However, since that point simply has never translated into increased market share, OS X is not the mainstay application target for most developers at present. I doubt the x86 build of OS X will change that.
