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

iPhone Air

Report: 'Virtually No Demand' for iPhone Air

Wednesday October 22, 2025 3:22 am PDT by
Apple is "drastically" cutting production of the iPhone Air and shifting focus toward the iPhone 17 and iPhone 17 Pro models, Nikkei Asia reports. The business publication claims to have learned of a major cut to iPhone Air production motivated by weaker-than-expected consumer interest, nearly to "end of production levels." Despite early reports of the iPhone Air selling out within hours of...
sam sung auction

Former Apple Employee Sam Sung Changed His Name to Avoid Attention

Wednesday October 22, 2025 4:44 pm PDT by
Back in 2012, an Apple retail employee named Sam Sung went viral because his name is similar to Samsung, one of Apple's main competitors. In a recent interview with Business Insider, he detailed that period in his life, how Apple responded, and he explained why he ultimately changed his name. Someone posted an image of Sung's Apple business card on Reddit in 2012, and it spread rapidly....
iOS 26

iOS 26.1 Coming Soon With These 8 New Features for Your iPhone

Wednesday October 22, 2025 6:15 am PDT by
The upcoming iOS 26.1 update includes a handful of new features and changes for iPhones, including a toggle for changing the appearance of the Liquid Glass design, "slide to stop" for alarms in the Clock app, and more. iOS 26.1 is currently in beta testing. The update will likely be released in the first half of November, and it is compatible with the iPhone 11 series and newer, but some...
cadillac lyric infotainment

GM to Remove CarPlay from All Future Vehicles, Including Gas Cars [Updated]

Wednesday October 22, 2025 11:34 am PDT by
General Motors began phasing out support for CarPlay in its electric vehicles back in 2023, leading to complaints from iPhone users, but the company has no plans to back down. In fact, GM is going further and plans to remove CarPlay from all future gas vehicles, too. In an interview with The Verge, GM CEO Mary Barra said that the company opted to prioritize its platform for EVs, but the...
All Screen iPhone 2027 Feature 1

Apple's Plan to Launch Three New iPhone Designs Allegedly Revealed

Wednesday October 22, 2025 6:24 am PDT by
Apple plans to launch a new type of iPhone every year for the foreseeable future, according to an Asia-based source. The detailed information was shared by the account "yeux1122" in a blog post on the Korean platform Naver, citing domestic trend and component research companies. Corroborating other reports, Apple will apparently launch its first foldable iPhone in 2026, featuring a...
All Screen iPhone 2027 Feature 1

Report: Apple to Skip 'iPhone 19' Name for 'iPhone 20'

Thursday October 23, 2025 4:28 am PDT by
Apple's new iPhone lineup launched in the fall of 2027 will be called the "iPhone 20" models, rather than the "iPhone 19," according to research firm Omdia. Speaking at a conference in Seoul (via ETNews), Omdia Chief Researcher Heo Moo-yeol corroborated rumors that Apple plans to move the launch of its standard iPhone to the first half of the year and provided some additional clarity about...
ios 26 1 liquid glass opaque

iOS 26.1 Beta 4 Lets Users Control Liquid Glass Transparency with New Toggle

Monday October 20, 2025 10:57 am PDT by
With the fourth betas of iOS 26.1, iPadOS 26.1, and macOS 26.1, Apple has introduced a new setting that's designed to allow users to customize the look of Liquid Glass. The toggle lets users select from a clear look for Liquid Glass, or a tinted look. Clear is the current Liquid Glass design, which is more transparent and shows the background underneath buttons, bars, and menus, while tinted ...
maxresdefault

Apple's iPhone Air Experiment Fails as Supply Chain Cuts Production by 80%

Wednesday October 22, 2025 10:48 am PDT by
iPhone Air demand failed to meet Apple's expectations and the company's supply chain is scaling back shipments and production, reports Apple analyst Ming-Chi Kuo. Subscribe to the MacRumors YouTube channel for more videos. Suppliers are expected to reduce capacity by more than 80 percent between now and the first quarter of 2026, and some components with longer lead times will be discontinued ...
apple wallet drivers license feature iPhone 15 pro

iPhone Driver's License Feature in Apple Wallet App Launches in Another U.S. State

Thursday October 23, 2025 7:44 am PDT by
In select U.S. states, residents can add their driver's license or state ID to the Wallet app on the iPhone and Apple Watch, providing a convenient and contactless way to display proof of identity or age at select airports and businesses, and in select apps. Starting today, the feature is available to residents of West Virginia. To set it up, open the Wallet app and tap on the plus sign in...