Microsoft rolled out Windows updates to address Meltdown and Spectre vulnerabilities in chipsets from Intel, AMD, and ARM, and since there’s been a lot of talk regarding the performance impact of these patches, the company decided to come clean and confirm that a slowdown is indeed happening.

Terry Myerson, Executive Vice President, Windows and Devices Group, explains in a lengthy post today that the impact systems are experiencing becomes more noticeable the older they get. This means that if your PC has the latest-generation silicon and runs on Windows 10, there’s a good chance you won’t notice anything different on a machine running the Meltdown and Spectre updates.

“These percentages are reflected in milliseconds,” Terry Myerson explained. Windows 10 devices with Skylake, Kaby Lake or newer CPUs are the least affected by the slowdowns, and the Microsoft exec says benchmarks showed only single-digit performance impacts.

Systems running Windows 10 on processors like Haswell and even older might experience “more significant slowdowns,” Myerson confirms, “and we expect that some users will notice a decrease in system performance.”

Noticeable slowdowns on Windows 7

Things are getting worse in the case of Windows 7 and Windows 8 on 2015-era CPUs, where the slowdowns caused by Meltdown and Spectre patches are the most noticeable, Microsoft says.

The same thing happens on Windows Server on pretty much any processors, and Myerson recommends IT admins to think twice before installing the patches. While it’s a bit surprising to hear Microsoft recommending against software updates, delaying deployment is less critical on Windows Server if these systems aren’t used for browsing or activities that could expose data to attacks, such as opening links facilitating exploits.

“Windows Server on any silicon, especially in any IO-intensive application, shows a more significant performance impact when you enable the mitigations to isolate untrusted code within a Windows Server instance,” Myerson explained.

As for why older versions of Windows and previous-generation processors are impacted by more significant slowdowns, Microsoft says they “have more user-kernel transitions because of legacy design decisions, such as all font rendering taking place in the kernel.” Detailed benchmarks will be published in the coming weeks to further analyze the slowdowns, Myerson promises.

“We’re also committed to being as transparent and factual as possible to help our customers make the best possible decisions for their devices and the systems that run organizations around the world,” the Microsoft executive concluded.