Image source: Apple.

Later this year, Apple (NASDAQ:AAPL) will release macOS Sierra, the next version of its Mac operating system. Sierra will bring a number of notable improvements to Apple's PCs, including support for Apple Pay and deeper integration with iOS devices.

It also brings Siri, Apple's digital personal assistant. Siri made her debut back in 2011, but it's taken Apple a full five years to bring her to the Mac. Nevertheless, her introduction could dramatically improve the productivity of Mac users, and give them a new way to interact with their machines. It could also pose a threat to Alphabet's (NASDAQ:GOOG) (NASDAQ:GOOGL) Google.

Siri comes to the desktop

Once they've installed Sierra, Mac users will be able to call on Siri by speaking to their machines. It's a bit of a shift from the familiar mouse and keyboard, but impressions have been generally favorable. Wired's David Pierce described the process of using Siri on the Mac as "almost natural" and "definitely useful." Ultimately, he concluded that Siri may be better on the Mac than she is on the iPhone.

In addition to her standard functionality, Mac Siri can conduct special Mac-related tasks, like searching local files or changing settings. iPhone users often find Siri most useful when they aren't actually using their phones at all -- Apple has trumpeted Siri's hands-free features as a key selling point in recent years. But on the Mac, she offers the prospect of improved multi-tasking. A Mac owner can use Siri to change a setting, play a song, or find a file without leaving their current application.

The inclusion of Siri probably won't help Apple sell that many more Macs, as competing machines running Windows 10 have something similar. Still, it does enhance Apple's offerings and ensures that the company is keeping pace with its rivals.

Cortana has helped Bing capture share

Perhaps more interesting is what Siri could do to the search market. Beyond finding files and changing settings, Siri can be used to scour the web. Since 2013, she's relied on Microsoft's (NASDAQ:MSFT) Bing to do so. Unless you specifically request Google, simple commands such as "find me chicken recipes" will result in Siri conducting a Bing search. Last December, research firm Kantar found that Siri relied on Bing frequently. Analyzing the behavior of 3,000 different Siri users, Kantar found that Bing powered 63% of the searches Siri conducted.

Microsoft's share of the U.S. search market has been rising in recent quarters. In July, 2015, Bing captured 20.4% of the U.S. desktop search market, according to comScore. Google's share was more than three times higher, at 64%. But over the last year, the gap has closed a bit. In June, comScore reported Bing's market share at 21.8%. Meanwhile, Google stood at 63.8%.

That shift has been driven by Windows 10 -- last quarter, over 40% of Microsoft's search revenue came from Windows 10 devices. Like macOS Sierra, Windows 10 includes a digital personal assistant: Cortana, which, unsurprisingly, is also powered by Bing. Cortana is integrated directly into the Windows 10 taskbar, and on many PCs can be summoned with a quick voice command. To date, Windows 10 users have asked Cortana more than 8 billion questions, and 100 million Windows 10 users rely on her each month.

Siri's addition to the Mac could have a similar effect. There are fewer Mac users than Windows users, obviously, but Siri could shift some search queries to Bing in the months ahead.

If Bing's share of the search market continues to rise, Microsoft may have Apple to thank.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.