What's so great about PPC? There's gotta be something

Question

With this question in mind (the first one that stackexchange is offering me right now among the "Questions with similar titles"), I'd like to steal the idea of the question and ask it about PPC.

What's so great about it? All other chips I've seen - ARM, MIPS, SuperH, x86 - crunch numbers just fine.

The background of this question - about PPC, that is - is that the PPC architecture is used in many DSP chips, in particular in the automotive industry. Of course, this could simply be a question of momentum, and allow the developers to stay with an architecture they know well, including the toolchain. And the software they've written until now, of course.

But assuming I'm starting a DSP project anew, without any old baggage to lug around - is there any compelling advantage of the PPC architecture that would persuade me to prefer PPC to, say, ARM?

Knowing about the power efficiency of ARM chips, let me mention that my design would run off the grid, not on batteries.

Answer 1

"What's so great about the PowerPC?"

There are so many ways to answer this question. It wouldn't surprise me if there is a book on the topic. I will answer it in the most concise and simple way possible and leave the details for the reader...

The PowerPC was a great processor because it was the right chip, for the right price, at the right time. For much of its life it was the fastest non-Intel CPU available (that was also commonly available). Compared to todays CPU's the PowerPC is just OK but at the time it was arguably the best. But in the current CPU market, ARM is the dominant non-Intel based CPU and the PowerPC is fading fast. Except for some very niche applications, there is no good reason to design a new product with a PowerPC CPU anymore.

As for DSP, there are so many other ways to get fast number crunching than to use a PowerPC. Only a few high-end versions of the PowerPC ever did well with DSP, that would be those with the Altivec instructions. But that is old technology and there are Intel and ARM processors that do just as good if not much better. There are also dedicated DSP chips that would be a modern alternative to the PowerPC for this application.

If you can use off the shelf PCB's then a modern Intel CPU can give you massive amounts of DSP power for relatively little cost. If you can't use an off the shelf PCB, and must make your own, then consider ARM chips or dedicated DSP chips (or ARM's with dedicated DSPs in them from T.I.). I say this without knowing your application, so take this advice with a huge grain of salt.

Answer 2

Once upon a time the x86 family were considered to be caught in a computing paradigm that demanded more and more megahertz and more and more transistors in order to keep up with comparitively simple RISC CPUs like PowerPC and ARM.

In short, the Intel CPUs at the time could be considered to be measured in CPU cycles per instruction, while the more modern architecture and RISC instruction set of the newer designs meant that they could measured in instructions per CPU cycle.

Enormous amounts of money and resources and exploring numerous dead-ends would eventually allow Intel and AMD to create x86 compatible chips that wrap CISC compatibility around a simplified RISC-like core to compete with the RISC designs on a level that seemed unlikely at the time.

Anyone creating a new computing platform at the time could see the writing on the wall, common thinking was that the x86 family were a technological dead-end, with even Intel putting their research efforts into RISC at the time with i960 then Itanium.

Meanwhile, in Apple's case at least, much of the early speed advantage of the more advanced PowerPC chips was squandered by users having to run most third-party software in emulation for a number of years.

By the time Apple had completed their 68k to PowerPC transition, Intel's revolutionary Pentium came along with similar price/performance and set the stage for PowerPC's fall from grace.

Answer 3

The simple answer for the modern advantage of PowerPC architecture is in real-time operation. There is a whole market for safety critical equipment where even a small unpredictable delay is a problem. Think brakes on a car, avionics controls for an aircraft, and anything to do with the space industry. A delay can kill people, or destroy millions of dollars of equipment.

If you are not using a Real-Time Operating System (RTOS) then this is probably completely irrelevant. Windows, and most flavors of Linux are useless for real-time operation, and the features of the OS ruin the real-time capabilities of the processor.

Intel never was great at real-time systems, and their processor "performance" improvements in the last decade have completely abandoned the principle. Intel performs active scheduling management in their processors, which is a problem with real-time, and have added predictive processing and other various improvements. For the common-user, this speeds up performance, but it is a problem for real-time operation.

There are some new ARM designs that are now reaching acceptable levels of real-time operation, but those are still significantly lower performance in processing power compared to a PowerPC.

Basically you can look at the market like this. Raw processing power, you want Intel. Low power usage, you want ARM. Real-time operation, you want PowerPC.