G5 bus speed


macrumors 68030
Original poster
Sep 13, 2001
Portland, OR
I was looking at the IBM PowerPC webpage, and I noticed an article about RapidIO. According to rumor (and according to both IBM and Motorola's PPC roadmaps) the G5 will use RapidIO. What was interesting is that the article said (if I understood it correctly) that RapidIO buses ran at four clock speeds: 125MHz, 250MHz, 500MHz, and 1GHz. So, if I understand this correctly, the G5 will have to have a bus at one of those four speeds. I *think* the top two (or at least the top one) speeds are theoretical because it seems unlikely that there would be that huge an increase in bus frequency. That leaves 125 and 250 Mhz. Since 125 would seem like a step down from the 133MHz bus on the G4 (emphasis on 'seem'), I would expect the 250MHz bus.

here's the article:


macrumors regular
Jan 18, 2002
RapidIO is used for CPU to CPU connections. This has nothing to do with memory bus speeds.

From the IBM page...
This new high-performance, packet-switched interconnect technology was designed for embedded systems, primarily for the networking and communications products.
It's more than likely that futue version of the PPC arcitecture will adopt AMD's Hypertransport protocol for CPU to CPU connections. I doubt the G5 will support this though as Hypertransport is realatively new.

Hope this helps.


macrumors newbie
Sep 3, 2001

running at 1GHz it can do 2315 MIPS
which seems to be about the same as a G4/G3 between 1250MHz and 1290MHz.

It has a lot of great features i think we might see in the G5
If you take a look at their roadmap, this actually is a G5 since it's 85xx.

333Mhz DDR controller, PCI-X, rapidIO etc.


macrumors regular
Jan 4, 2002
There's a good article at Extremetech about the various emerging technologies for fast I/O. They all have slightly different aims. Things to note:

Rapid IO and Hypertransport have less ambitious aims than 3GIO and Infiniband. All of them use point-to-point architectures, most of them serial.

Apple is a founding member of the Hypertransport Consortium. Motorolla is the biggest proponent of RapidIO. IBM is a key backer of infiniband. 3GIO is led by Intel, MS, HP, and Compaq.

3GIO is expected to coexist with or eventually displace Hypertransport. RapidIO is meant mainly for embedded communications.

Infiniband is intended for server-to-server applications, and permits powerful, flexible, scalable, hot-pluggable, and novel architectures in the storage-area network. The elements of a computer - processing and memory, storage, ethernet, power, and other functionalities - are separated and communicate via Infiniband abstractions. This allows each functionality to be improved and supplemented as needed with much less complexity, a tremendous boon to internet datacenters.

Not mentioned is the system-area network including VI (virtual interface), which allows message passing between processes on different chips, nor clumping or memory sharing. These allow powerful computation, a boon to scientific and industrial analysis.

And here's my speculation - well, more like a hope: Gigawire might be redesigned to be backwards compatible with regular firewire, as well as offering new protocol functionality that would allow ALL the functionalities of your system - including processing power - to be upgraded with internal or external devices, or even a separate computer. This would allow easier PC upgrading, powerful supercomputing systems/networks, and supercapable data servers.
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