I just got the new book by IBM PowerPC engineers David Shippy & Mickie Phipps, "The Race for a New Game Machine", that explains how they were two-timing Sony & Microsoft in the development of their video game CPUs.
The PS3 & Xbox 360 contain what eventually would have been the G6.(This is my read, not specifically given in the book)
In a quick scan, I found a couple of interesting claims: Apple was being told to expect 6Ghz clock speeds from IBM. This would help explain why Steve Jobs promised 3Ghz so confidently.
A big part of Apple's decision to drop IBM PowerPC was when IBM proposed that Apple accept the loss of Out-of-order execution in the new CPU (the potential G6), because that is what was best for video games. The PS3&Xbox360 CPU did eliminate out-of-order execution.
As you might recall, the G5 was well known for the ability to have 200 instructions in-flight. Without OOE, this would have dropped dramatically, and Apple performance in general purpose single-thread execution would have plummeted. It might have been possible to compensate with more cores, but of course, the OS and apps would certainly have not been ready in 2005 to really make that happen. (It barely works today!)
Intel has proposed future chips may also drop OOE, but hasn't done so yet. In fact, they have brought back another method of leveraging the OOE hardware, by adding Hyper-threading back to their upcoming/new chips.
The book notes that Apple was not an important factor, because Apple did not pay for their CPU development & had low volumes, while Sony&MS paid for development, and promised high volume.
The timelines are fuzzy, but it certainly looks like Apple knew within a year of the first G5 release that they needed a new boat. PowerMac G5 shipped June 2003, development of the PS3& Xbox360 was heavily underway in 2004 (to target a late 2005 Xbox ship), and Steve announced the transition in June/July 2005.
The PS3 & Xbox 360 contain what eventually would have been the G6.(This is my read, not specifically given in the book)
In a quick scan, I found a couple of interesting claims: Apple was being told to expect 6Ghz clock speeds from IBM. This would help explain why Steve Jobs promised 3Ghz so confidently.
A big part of Apple's decision to drop IBM PowerPC was when IBM proposed that Apple accept the loss of Out-of-order execution in the new CPU (the potential G6), because that is what was best for video games. The PS3&Xbox360 CPU did eliminate out-of-order execution.
As you might recall, the G5 was well known for the ability to have 200 instructions in-flight. Without OOE, this would have dropped dramatically, and Apple performance in general purpose single-thread execution would have plummeted. It might have been possible to compensate with more cores, but of course, the OS and apps would certainly have not been ready in 2005 to really make that happen. (It barely works today!)
Intel has proposed future chips may also drop OOE, but hasn't done so yet. In fact, they have brought back another method of leveraging the OOE hardware, by adding Hyper-threading back to their upcoming/new chips.
The book notes that Apple was not an important factor, because Apple did not pay for their CPU development & had low volumes, while Sony&MS paid for development, and promised high volume.
The timelines are fuzzy, but it certainly looks like Apple knew within a year of the first G5 release that they needed a new boat. PowerMac G5 shipped June 2003, development of the PS3& Xbox360 was heavily underway in 2004 (to target a late 2005 Xbox ship), and Steve announced the transition in June/July 2005.