Hammerhead memory interleaving......

[DearthnVader]

I thought I'd bring up an old topic about PCI Old World Powermacs with the Hammerhead memory controller( 7300-7600, 85/8600, 95/9600, PowerTower Pros, S900's Genesis). For those of you that don't know the memory in these systems can be "interleaved" to improve performance.

Here is an old article on how much speed performance one might expect:

Macs and Interleaved RAM tests

Welcome to Accelerate Your Mac's Memory Interleaving performance comparisons. Just what apps gain from interleaving? How much does it help?

web.archive.org

Since these old systems generally have a bottleneck around memory and bus speeds, every little bit of performance we can can get out of them helps.

I do have a question tho, what happens if we mix memory?

I have 32MB A1 32MB B1 64MB A2 64MB B2 and a single stick of 64MB B6, does this configuration disable interleaving or can the Hammerhead handle some memory the is interleaved while other memory that is not?

As time allows I'll be benchmarking my 9600 with some more modern apps and hardware/OS that is listed in the old Xlr8yourmac article, but does anyone have a copy of the memory bandwidth benchmark Mike used for that article?

 

[DearthnVader]

I did a few tests with PCI disk controllers, one SATA SlI3112 and one ATA.

These disk controllers don't preform great in my PM9600 as far as pure throughput, even tho the system should have the max theoretical throughput of 33mhz PCI( 133MB/s ). In the real world these systems greatly under preform that.

With the RAM interleaved I did see between 10%-15% gains in disk speed. Still not great, peaking around 29MB/s. Tho with the RAM non-interleaved I saw peaks around 26MB/s. Still much faster the the peak performance of the built-in OEM 4GB SCSI disk that peaked about 8MB/s.

With the RAM non-interleaved GagePro reported a moving memory rate of 39MB/s vs. 62MB/s with it interleaved.

Quake3 also showed about a 10% gain in FPS in a time demo with the memory interleaved.