A History of PowerPC

A reader writes: "There's a article about chipmaking at IBM up at DeveloperWorks. While IBM-centric, it talks a lot about the PowerPC, but really dwells on the common ancestory of IBM 801" Interesting article, especially for people interested in chips and chip design.

Comments

*sigh*

[nocomment]

I still want a PPC ATX board. Pegasos was supposed to deliver, but their boards are still so expensive. :-(

Nice 42 year backward compatibility

[JohnGrahamCumming]

From TFA:

"Today's IBM mainframes still maintain backwards-compatibility with that revolutionary 1962 instruction set."

Good plan then, Intel, on that whole Itanium mess.

John.

Power PC was the death of the MIPS processor

[MrIrwin]

Not that it was necessarily a bad think, but with the PowerPC came a whole new generation of workstation.

Gone where the intelligent disk and network subsystems. No more die cast aluminimum chassis.

Whilst I can understand in some sectors the incessant drive for highest MIPS per $, is there not also a place for bullet proof proven technology?

Computer history IS IBM-centric

[Random BedHead Ed]

I don't see how computer history that goes back to the 1960s can fail to be "IBM-centric." Remember, these were the big guys Microsoft was afraid of pissing off in the 1970s and 1980s. No one ever got fired for buying IBM, because they pretty much wrote the book on chip design before Intel hit it big.

200 instructions at once?

[Phs2501]

I think it's quite imprecise writing for the article to state (several times, for POWER4 and the PowerPC 970) that they "can process 200 instructions at once at speeds of up to 2 GHz." That makes it sound like they can finish 200 instructions at once, which is silly. I imagine what they really mean is that there can be up to 200 instructions in flight in the pipeline at a time.

(Which is great until you mispredict a branch, of course. :-)

I like this quote

[Zo0ok]

The 64-bit PowerPC 970, a single-core version of the POWER4, can process 200 instructions at once at speeds of up to 2 GHz and beyond -- all while consuming just tens of watts of power. Its low power consumption makes it a favorite with notebooks and other portable applications on the one hand, and with large server and storage farms on the other.

Can anyone tell me where I can buy a G5 laptop?

Don't ignore integer sizes!

[Dog135]

Expanding the data to 64 bits has no effect on existing code, whereas the big-endian case will have to change all the pointer values

So, you're reading in an array of integers, which are now 64 bit vs 32 bit and no code change is needed?

Programs NEED to know the size of the data they're working with. Simply pulling data from an address without caring for it's size is a recipee for disaster!

that's not what RISC really turned out to be

[Anonymous Coward]

RISC made each instruction simple. That's how the name was chosen. But the point of machine each instruction simple was so that every transistor could be used in each cycle. By using every transistor, you maximize your performance on a per-transistor basis.

So, to do this, you drop specialized functionality. This meant simplifying the instruction set.

But that produced code bloat, because to really follow the idea you have to ditch stuff like dividers. Dividers are very difficult to fit into a pipeline and so the proper way to follow the mantra is to to expand a division into 32 separate instructions that do one step of the process (or 17 stages with other dividing methods). These 32 instructions could be pipelined, and thus you maximized your transistor reuse.

But this leads to code bloat. At the minimum, you have to do some call setup and takedown to call a division function. So that hardware was put back in. And other hardware followed, until even specialized vector units are allowed.

CISC can produce good performance also if they can utilize all their transistors better.

Re:Yeah, I remember

[Bert64]

Well Motorola hoped the PPC would be the successor to the M68k, a very successfull processor that was very widely used, easy to program for and very good for learning assembly on.