[DekuDekuplex]

According to Apple's PowerBook G4 Processor Web Site,

The PowerPC G4 Velocity Engine processes information in 128-bit chunks, compared to the 32- or 64-bit chunks in traditional chips.

This seems to indicate that the PowerPC G4 chip is a 128-bit CPU.

However, according to Apple's G5 Execution Core Web Site,

the PowerPC G5 chip uses the same set of 162 instructions as the G4. See below:

Optimized Velocity Engine

The PowerPC G5 uses an optimized dual-pipelined Velocity Engine with two independent queues and dedicated 128-bit registers and data paths for efficient instruction and data flow. This vector processing unit accelerates data manipulation by applying a single instruction to multiple data at the same time, known as SIMD processing. The Velocity Engine in the PowerPC G5 uses the same set of 162 instructions as in the PowerPC G4, so it can run � and accelerate � existing Mac OS X applications already optimized for the Velocity Engine.

So, just how many bits is the G4?

DekuDekuplex

[RMXO]

Originally posted by DekuDekuplex:
According to Apple's PowerBook G4 Processor Web Site,



This seems to indicate that the PowerPC G4 chip is a 128-bit CPU.

However, according to Apple's G5 Execution Core Web Site,

the PowerPC G5 chip uses the same set of 162 instructions as the G4. See below:



So, just how many bits is the G4?

DekuDekuplex

correct me if im wrong but isnt the author talking about the Velocity Engine being able to handle 128bit? i think its talking about Velocity Engine & not the actually CPU itself. G4 CPU's are 32bit right?

[The Placid Casual]

Originally posted by RMXO:
correct me if im wrong but isnt the author talking about the Velocity Engine being able to handle 128bit? i think its talking about Velocity Engine & not the actually CPU itself. G4 CPU's are 32bit right?

Yep, they are talking about Altivec only when they mention 128 Bits.

Yep, the G4 is 32 bit.

[The Godfather]

Velocity engine is the math unit inside the CPU.

The math unit (aka ALU, FPU) is 128 bits in the G4, but its RAM addressing is 32 bit. This means that, internally, it can operate a pair of 128-bit numbers in one clock cycle. It also means that it can handle 2^10*2^10*2^10*2^2=4GB of RAM.

In the G5, the RAM addressing is of 64 bits. Theoretically, the CPU can address 4 billion times more memory, or 18.4 Exabytes (10^18). If they say they have dual pipeline Altivec, then they can make 2 128-bit operations at the same clock... I think.

If the world economy can support the creation of Exabyte memory chips, the applications will be truly from Science Fiction

[Simon]

Originally posted by The Godfather:
Velocity engine is the math unit inside the CPU.

The math unit (aka ALU, FPU) is 128 bits in the G4, ...

Just a little correction here.

Velocity Engine or Altivec (as Moto calls the instrcution set) is a vector processing unit. That means it calculates not just floats but vectors. It can permutate them, add them, etc..

The FPU however is the "math unit" as you called it, because it is responsible for the floating point operations. Like 5.2e-13 / 3.141592.

Note that math can also be done by the integer processing unit. It depends on the code you write.

The Intel PIII and P4 have of course a FPU as well as the G3, G4 and G5. But only the G4 and the G5 have a Velocity Engine.

Actually, to make stuff worse, a new G3 coming out probably soon called Gobi which is a PPC 750gx made by IBM also has a Velocity Engine even though the original G3 (and the 750fx) didn't.

And as a rule of thumb: G4 (7450, 7455, etc.) = G3 (750, 750fx) + Velocity Engine. However, the G5 is a whole new ball game.

[DekuDekuplex]

Originally posted by Simon:
Just a little correction here.

[stuff deleted]

Actually, to make stuff worse, a new G3 coming out probably soon called Gobi which is a PPC 750gx made by IBM also has a Velocity Engine even though the original G3 (and the 750fx) didn't.

And as a rule of thumb: G4 (7450, 7455, etc.) = G3 (750, 750fx) + Velocity Engine. However, the G5 is a whole new ball game.

So, which will be faster, and by how much (or will they both run at the same speed): Gobi, or the current 1 GHz PowerPC G4 in the 17-inch PowerBook?

Also, how soon is Gobi scheduled to be released?

DekuDekuplex

[Commodus]

According to what I've seen, Gobi doesn't include Altivec - it's just a 750FX (current-generation G3) with 1 MB of L2 cache and a faster system bus. It's the Mojave that tacks on Altivec.

That makes for an interesting dilemma if true; is Apple going to continue making the existing iBook design with a 1 (or 1.1) GHz Gobi in it and then revise the line later? Or are they going to make G4 (Motorola-based) iBooks and then move the PowerBook on to G5s?

[Simon]

Originally posted by Commodus:
According to what I've seen, Gobi doesn't include Altivec - it's just a 750FX (current-generation G3) with 1 MB of L2 cache and a faster system bus. It's the Mojave that tacks on Altivec.

Ah darn. I goofed on the codenames again. Thanks for pointing it out. Gobi + Altivec = Mojave.

That makes for an interesting dilemma if true; is Apple going to continue making the existing iBook design with a 1 (or 1.1) GHz Gobi in it and then revise the line later? Or are they going to make G4 (Motorola-based) iBooks and then move the PowerBook on to G5s?

Yeah, this will put Apple in a tight sqeeze. What will they do? They could

- continue to market the iBook as a G3 and stick with Gobi which will take them up to 1.1GHz and give better performance at the same clock due to the improved cache and bus.

- take the iBook line to the G4. But with what CPU? They could use a 7455 or 7457 or they could use a VE-equipped G3 like Mojave and market it as a G4.

- what about the iMac and eMac? Assuming they're not going G5 very soon they need a VE-equipped CPU that will keep going for at least another year. The 1.42GHz 7455 is probably moot. What about 7457? Or maybe a Mojave?

- the same for the PowerBooks. They need a fast G4 but it shouldn't consume too much power. The Mojave sounds more approriate for the job than a 7455. But, what about the 7457 and the 7457-RM?

The idea of Apple selling a Mojave as a G4 is certainly not deception. Actually, Mojave is for IBM what Moto did with the 7450. Slap on a VE to a G3 core. Only, IBM did it better, because they improved cache and bus as well. So maybe a Mojave will beat a 7455 at the same speed. However, it could be rather equal to the new 7457 which also has better cache and bus than the 7455. And if Moto would get their fingers out and finally make a 7457-RM with true fast DDR bus and on-dye cache that could really be nice competition for Mojave.

But generally, Apple's in a good situation. They have a stadard chip design plattform (the PowerPC) and several model that comply to those specs and compete with each other. Steve might as well sit back, wait and then just go see what CPU offers the most power, dissipating the least heat at the best price. And then just solder it to the new boards.

[tooki]

OK, here's the real deal:

- integer processing unit: deals with whole numbers (and if you don't specifically use workarounds, it'll tell you that 2.6+2.6=4, since it can't deal with decimals) used extensively by classic Mac OS, Windows, etc, used on all OSes for most core processes

- floating-point processing unit: deals with numbers with decimals (and often can't represent whole numbers accurately, so the number 2 may in fact be stored as 1.99999999999999999). used extensively by Mac OS X, and on all OSes in some applications like 3D and mathematical apps

- vector processing unit, aka AltiVec, aka SIMD (single instruction, multiple data). This is for things like multimedia or Photoshop filters, where the same tasks are being repeated over and over for a stream of data. used extensively by Mac OS X, used in some OSes in some applications, like video, filters, etc

The G4 has 32-bit integer and floating-point units, and 128-bit vector.

The G5 has 64-bit integer and floating-point units, and 128-bit vector.

Additionally, all the remaining parts of the processors (there are tons of support units) are 32-bit for the G4 and 64-bit for the G5.

tooki