Slashdot Mirror
Design Philosophy of the IBM PowerPC 970
D.J. Hodge writes "Ars Technica has a very detailed article on the PowerPC 970 up that places the CPU in relation to other desktop CPU offerings, including the G4 and the P4. I think this gets at what IBM is doing: 'If the P4 takes a narrow and deep approach to performance and the G4e takes a wide and shallow approach, the 970's approach could be characterized as wide and deep. In other words, the 970 wants to have it both ways: an extremely wide execution core and a 16-stage (integer) pipeline that, while not as deep as the P4's, is nonetheless built for speed.'"
Kudos to the Ars team yet again for going deeper into CPU designs than 99% of the populace need to go :)
This chip could be the start of something big in the Linux space as well. Think about it, we are now at a point where a few companies other than Intel are now poised to take the center stage in the next gen workstation, most notably AMD, Apple, and now IBM themselves.
While Linux has run on PPC chips for a long time, it is difficult to come upon a G4 chip without paying the "Apple Tax" for the hardware. If IBM steps up to the plate with this chip, which can then run OS X, Mach, Linux, *BSD, (insert other OS'es here), and can be purchased directly or in a package from IBM, we may see a good set of Windows challengers for the desktop and server room. Obviously OS X will still only run on Apple derivatives.
These chips will be big, I guarantee it, and not just for Apple. It will be interesting to see if Microsoft ports Win XP to these chips.
Why would they want to?
Intel and AMD have the x86 market pretty well locked down.
More importantly, why would ANYBODY want to implement the x86 ISA (Instruction Set Architecture or smtn like that). It's the most horrid instruction set in use today.
Some instruction sets can't really be mapped to others easily, and optimizing for good performance with PPC would probably not have good x86 performance anyways.
In Pentiums and Athlons, the instruction set isn't really emulated. It's translated to a smaller instruction set (uops, iops, pick whatever term you like and run with it). However, these smaller sets are still made pretty much specifically to cover the overlying ISA (x86 in this case).
I think Apple will stick with a company that it knows, IBM, since they have been working together for years. It doesn't seem that Apple will just jump ship to the x86 platform. This would also mean redoing the Mac OS X code and optimization (not like they will have to do some anyway, but they will have to do more). It is highly unlike that Apple will go with a heat producing, energy wasting x86 Intel chip.
Apple will almost certainly go with 970 and not switch to Intel for the following reasons: 1. It is difficult to emulate PowerPC with Intel (although the reverse isn't *that* difficult). Apple would need a PowerPC emulator so that all that software (including OSX software) isn't lost. 2. Apple wants to differentiate itself somewhat from the PC. 3. IBM appears to be moving up after the several years of problems with Motorola. The downside is that by the time a 970 board is out it will definitely be in the middle of the pack relative to the PC world. That means that Apple still will have computers that are more expensive than the PC world and that aren't as fast. Of course I think OSX is sufficiently better than either Linux or WinXP for a workstation that I'll stick with it. But Apple best hope that IBM gets large yields on time and perhaps with better speeds than expected.
finally they'll see that clock speed does make a difference Clock speed is something Intel uses to bolster their performance claims and give people an excuse to upgrade to the newest model. Clock speed tells very little about the performance of a computer. Look at AMD's athlon. Many reviews like the ones on tom's hardware show that running Windows on a "slower" athlon yeilds better performance than a comparably clocked P4. If you meant that finally, if apple runs on x86, there will be a better benchmark between Windows and MacOS, you would be more accurate. Until that happens you are comparing two different fruits.
0xfeedface
...an extremely wide execution core and a 16-stage (integer) pipeline that, while not as deep as the P4's, is nonetheless built for speed.
:-)
For those not planning to read the article, I wanted to mention the following so you do not get the wrong impression. The speed that the article refers to (of a long integer pipeline, like a 16-stage or like the Pentium IV's 20-stage) is clockspeed, not necessarily actual performance. The P4's super long pipeline, for example, allows it to run at higher clock speeds, but less work gets done in the same number of clock cycles. This is the "braniac" vs "speed demon" philosophy (with a high clock speed but low instructions-per-clock representing "speed demon") and neither is necessarily better than the other (though one is obviously better for the marketing dept.)
Just don't assume that "built for speed" always means "built to be fast" -- a confusing but important distinction.
Computer Science is no more about computers than astronomy is about telescopes. --E. W. Dijkstra