G5 Processor and Bus Slewing (Speed Control)

A Spymac thread posted this weekend reveals some screenshots and information about a feature of the new PowerMac G5's called "Slewing".

The feature is located in the Energy Saver Control Panel and allows the user to make some modifications to the Processor and Bus performance settings. A concept that is familiar to laptop owners... the G5 can be run in Reduced, Highest and Automatic performance settings.

Details on the various modes are provided in Apple's Developer Documentation.


    To lower power consumption, heat generation, and fan noise, the Power Mac G5 computer incorporates an automatic power management technique called bus slewing. Bus slewing is designed to run at high processor and bus speeds and high voltage when the demand on the processor is high, and to run at low processor and bus speeds and low voltage when the demand on the processor is low.

Speed ranges involved start from 1.3GHz up to the highest rated GHz of the chip (1.6, 1.8, or 2.0). The default slewing option for the PowerMac G5s is Automatic, and the processor and bus speeds are modulated seamlessly to the user.

According to our contacts, there should be no performance loss in Automatic mode.

That being said, at least one user (in the previously mentioned thread) claims an 11 point increase in their Xbench score after changing their Slewing mode from Automatic to Highest. However, readers are reminded that XBench has been inconsistent in producing reproducible benchmark numbers -- even on the same machine. MacRumors' reader 1stunna managed to get a 11 point increase in Xbench scores by simply rerunning the test three times, with no other changes to the system. Whether this represents test-to-test variability or a side-effect of the processor automatically ramping up is still up for debate.

Update: More details found in this Ars Thread:


    The ramp time up or down is ~1ms, but the CPU is running normally during this time, so there is no performance "hiccup". This results in about 60% power/heat savings, which jumps up to about 85% savings if the machine is idle and they "turn on other power saving features". When idle, the CPU fans are barely turning.
Related Roundup: Mac Pro
Buyer's Guide: Mac Pro (Neutral)
Related Forum: Mac Pro

Popular Stories

iOS 26

iOS 26.4 and iOS 27 Features Revealed in New Leak

Friday December 12, 2025 10:56 am PST by
Macworld's Filipe Espósito today revealed a handful of features that Apple is allegedly planning for iOS 26.4, iOS 27, and even iOS 28. The report said the features are referenced within the code for a leaked internal build of iOS 26 that is not meant to be seen by the public. However, it appears that Espósito and/or his sources managed to gain access to it, providing us with a sneak peek...
Apple Logo Top Half

Early iOS 26 Software Leak Uncovers Dozens of Upcoming Apple Features

Monday December 15, 2025 3:05 pm PST by
Software from an iPhone prototype running an early build of iOS 26 leaked last week, giving us a glimpse at future Apple devices and iOS features. We recapped device codenames in our prior article, and now we have a list of some of the most notable feature flags that were found in the software code. In some cases, it's obvious what the feature flags are referring to, while some are more...
apple beta 26 lineup

Apple Leak Confirms Work on Foldable iPhone, AirTag 2, and Dozens More Devices

Monday December 15, 2025 2:05 pm PST by
Last week, details about unreleased Apple devices and future iOS features were shared by Macworld. This week, we learned where the information came from, plus we have more findings from the leak. As it turns out, an Apple prototype device running an early build of iOS 26 was sold, and the person who bought it shared the software. The OS has a version number of 23A5234w, and the first...
Apple Foldable Thumb

Leak Reveals Foldable iPhone Details

Monday December 15, 2025 9:09 am PST by
The first foldable iPhone will feature a series of design and hardware firsts for Apple, according to details shared by the Weibo leaker known as Digital Chat Station. According to a new post, via machine translation, Apple is developing what the leaker describes as a "wide foldable" device, a term used to refer to a horizontally oriented, book-style foldable with a large internal display....
iOS 26

iOS 26.3 Beta 1 Features: What's New So Far

Monday December 15, 2025 4:23 pm PST by
Apple is testing iOS 26.3, the next version of iOS 26 that will launch around January. Since iOS 26.3's testing is happening over the holidays, it is a smaller update with fewer features than we've seen in prior betas. We've rounded up what's new so far, and we'll add to our list with subsequent betas if we come across any other features. Transfer to Android Apple is making it simpler...
iOS 26

Apple Releases iOS 26.2 With Alarms for Reminders, Lock Screen Changes, Enhanced Safety Alerts and More

Friday December 12, 2025 10:10 am PST by
Apple today released iOS 26.2, the second major update to the iOS 26 operating system that came out in September, iOS 26.2 comes a little over a month after iOS 26.1 launched. ‌iOS 26‌.2 is compatible with the ‌iPhone‌ 11 series and later, as well as the second-generation ‌iPhone‌ SE. The new software can be downloaded on eligible iPhones over-the-air by going to Settings >...
iOS 26

iOS 26.2 Coming Soon With These 8 New Features on Your iPhone

Thursday December 11, 2025 8:49 am PST by
Apple seeded the second iOS 26.2 Release Candidate to developers earlier this week, meaning the update will be released to the general public very soon. Apple confirmed iOS 26.2 would be released in December, but it did not provide a specific date. We expect the update to be released by early next week. iOS 26.2 includes a handful of new features and changes on the iPhone, such as a new...
airpods max 2024 colors

AirPods Max 2 Likely to Offer These 10 New Features

Monday December 15, 2025 7:41 am PST by
Apple released the AirPods Max on December 15, 2020, meaning the over-ear headphones launched five years ago today. While the AirPods Max were updated with a USB-C port and new color options last year, followed by support for lossless audio and ultra-low latency audio this year, the headphones lack some of the features that have been introduced for newer generations of the regular AirPods and the ...