New Power Macs Have Crippled DDR Memory?

eggboard writes "According to Rob Art Morgan, who has tested this, the new Power Macs from Apple that use DDR (double data rate) memory -- like the Xserve rank-mount unit -- cannot access the memory any faster than the cheaper and slower SDRAM found in the previous system arch. A controller limits the data rate to 1 GB/s, while DDR could work more than twice as fast. Unfortunately, this makes mincemeat of the architecture, as it bus-/memory-bounds 2D and 3D graphics and rendering."

Comments

Re:Meet the new boss...

[foobar104]

You haven't the slightest idea what you're talking about, do you?

Motorola makes the CPU. Motorola makes CPUs that don't support DDR access to memory.

Apple makes the motherboards. Apple implements DDR memory everywhere except in the CPU.

IBM just announced vector computing support in the Power4. Vector computing is a big part of Apple's strategy, and until recently it was only available from Motorola.

The new Power Macs have a heat dissipation mechanism that's capable of dealing with many times the heat load of the currently shipping systems. They added this feature despite the fact that the previous generation of Power Macs had no particular heat problems.

Can't you read the writing on the wall? Apple has designed this new Power Mac to accept new, faster processors, and lots of 'em. A four-processor system is not unreasonable given the amount of space and heat dissipation inside this new chassis. Six or eight processors might even be possible, if everything comes together just right.

Don't assume you have the first idea what Apple has planned until you get all the facts.

These so-called benchmarks

[Gil Da Janus]

are really badly done.

The base configs of each machine are NOT listed.

The base OS configs of each machine are NOT listed.

The combined running configs, ie, size of objects, optional software (especially 3rd party apps and gui-players), etc, etc.

Guess what - each of the above - without running a single line or click of a benchmark can help in determining the outcome.

I'll wait to see how bad or good the new machines are - but I can tell you in advance, the old dual 1Ghz machines and the new ones are not identical at all in the CPU area.

Some folks have to learn to read and understand specs before jumping up and down and screamming.

Just my 2 cents, from the peanut gallery here in NY

Gil

Graphics/rendering bus-limiting remains untested

[tbmaddux]

A controller limits the data rate to 1 GB/s, while DDR could work more than twice as fast. Unfortunately, this makes mincemeat of the architecture, as it bus-/memory-bounds 2D and 3D graphics and rendering.

The data rate between CPU and RAM is limited to 1.3 GB/s. However there is still more than 1.3 GB/s of bandwidth for the GPU (AGP 4x which goes at about 0.5 GB/s), DMA calls from hard disks, etc. So graphics and rendering are not strictly bus-limited, as the GPU can never fully stress the bus. Furthermore, the GPU wasn't tested in the BareFeats benchmarks!

Furthermore, don't forget that the L3 cache on the new 1GHz Macs is only 1 MB, not 2 MB as it was in the previous 1GHz Macs (and as it remains in the 1.25 GHz Macs).

All these benchmarks teach us is that CPU-limited tasks like those posted at BareFeats are not a good test of the added throughput between the system controller and RAM. We need to see benchmarks that stress all of the throughput, not just the portion between CPU, controller, and RAM.