Troubleshooting the Power Mac G5: Questions about RAM speed, installation; ADC KVM switch - keyboard and mouse problems

Questions about RAM speed, installation The Power Mac G5 uses DDR 400 memory. However, buyers may be confused by which modules to buy, as different types use different CAS latency rates. The lower the number, the better, and more expensive.

CAS Latency is a number that refers to the ratio between column access time and the clock cycle time. According to a description at SysOpt.com, it is derived from dividing the column access time by the clock frequency, and raising the result to the next whole number. SysOpt.com also notes " In general, the importance is nominal. CAS3 means, at 100 Mhz., that the amount of time required for the first memory access in a burst is increased by less than 10 ns. Divide that by 4, to average the increased time across four bursts, and you have an improvement of less than 2.5 ns. over CAS2."

It is as of yet unclear whether Apple uses CAS3 or CAS2 memory stock in shipping G5s. This is important, because even if you install faster CAS2 memory in the system, all of the RAM will run at the slowest speed. One rotten DIMM spoils the whole bunch.

That said, it is apparent (though not fully confirmed) that the Power Macintosh G5 is fully capable of supporting CAS2 memory. And, you can get a CAS2 1 GB RAM module for less than US$200.

So while you can pull any stock memory from your Power Macintosh G5, install all low-latency RAM, and possibly enjoy a modest speed gain, standard DDR 400 PC3200 modules are guaranteed to work well with and carry adequate bandwidth for the Power Macintosh G5.

You can check your current RAM CAS latency by running the Apple Hardware Test CD, shipped with all Mac models, which will display the memory timing specifications.

ADC KVM switch - no keyboard and mouse functionality Anthony Lucente describes a conflict between the Power Macintosh G5 and the ADC KVM switch from IOGear - one of many minor hardware incompatibilities bound to appear over the next few weeks with the shift in system architecture:

"I'm using a IOGear Miniview ADC KVM with a 17" Apple Studio Display shared between a Dual 1.0 GHz G4 and a 1.8 GHz G5. With the keyboard and mouse plugged into the back of the monitor when ever I startup the G5 (with the KVM selector set for either machine) the G5 doesn't seem to recognize them (the keyboard and mouse). Not only that but if I then unplug the keyboard and mouse from the monitor and plug it into any of the G5's USB ports it still doesn't get recognized. However, it still works fine on the G4."

The only solution so far is to shut down the Power Mac G5, set the KVM selector for the G5 and move the keyboard and mouse from the monitor USB port into any of the G5's USB ports. Once the Power Mac G5 is up, you can then move the keyboard and mouse back to the USB port on the monitor. Once started this way switching between the machines works as expected.

Feedback? Late-breakers@macfixit.com.

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