Google yesterday advanced its 64-bit Chrome browser to beta status, and told owners of the very earliest Intel-based Macs that they would soon be left behind.

The promotion of the 64-bit Chrome for OS X to the "Beta" channel followed a move earlier this month by Google to push the browser to the rougher-edged "Dev" build. It also came on the heels of Chrome 64-bit for Windows making it to the more-polished "Release" status on Tuesday.

Google trumpeted the 64-bit Chrome for Mac as faster to start, less of a memory hog and more secure.

"Most programs on a modern Mac are already 64-bit apps," Mark Mentovai, a Chrome software engineer, said in a Thursday blog. "In cases where Chrome was the last remaining 32-bit app, there were launch-time and memory-footprint penalties as 32-bit copies of all of the system libraries needed to be loaded to support Chrome. Now that Chrome's a 64-bit app too, we expect you'll find that it launches more quickly and that overall system memory use decreases."

Chrome has long had a voracious memory appetite, in part because of its design, which runs each tab as a separate process. That feature allows Chrome to continue running even when individual tabs crash.

Like the 64-bit Chrome for Windows, the one for OS X does not support older 32-bit plug-ins in the NPAPI format. NPAPI (Netscape Plug-in Application Programming Interface), goes back to Netscape, the 1990s browser that Microsoft drove out of the market. Google has already blocked all but a handful of NPAPI plug-ins from running in 32-bit Chrome, although a few have been whitelisted and will still work, including Microsoft's Silverlight.

There are 64-bit versions for the most popular plug-ins, including Silverlight and Oracle's Java. Because Adobe's Flash Player is baked inside Chrome, a plug-in is unnecessary.

Google has not yet set a timetable for scrubbing all NPAPI plug-ins from Chrome, but next month the company will yank Web apps and add-ons which use NPAPI from the Chrome Web Store.

Unlike with Chrome for Windows, the Mac browser will not be maintained in separate 32- and 64-bit versions: People running the beta will automatically be updated to the latter. And when Chrome 38 reaches Release status, the 32-bit Chrome will be retired.

While Google does not hew to a definitive release schedule for Chrome, as does Mozilla's Firefox, it upgrades Chrome about every six to eight weeks. Because Chrome 37 shipped on Tuesday, the first 64-bit-only browser for OS X will probably debut in mid-October.

At that point, some Mac users of Chrome will either have to switch browsers -- likely to Firefox, which includes both 32- and 64-bit versions in each edition's package -- or risk running an unpatched browser.

"Those few users with first-generation Intel Macs will miss out on the fun, but as we bid them farewell, we'll remind them that they'll still be able to run the latest version on the stable channel, Chrome 37," said Mentovai.

Apple announced the switch from the PowerPC line of processors to Intel CPUs in early 2005, and started to sell Intel-based Macs in January 2006. The first-generations of Intel Macs relied on 32-bit processors, but by August 2007, the transition to 64-bit was complete.

Thus, Macs sold by Apple from January 2006 to August 2007 at the latest will not be able to run the 64-bit Chrome. (Individual models made the 32-bit to 64-bit at different times: The MacBook Pro, for instance, went 64-bit in June 2007, while the less-expensive MacBook switched to 64-bit in November 2006.)

OS X 10.6, aka Snow Leopard, which was released in August 2009, was the last edition that supported 32-bit Intel Macs. Snow Leopard has resisted retirement more than any other recent edition of OS X -- in July it still ran on an estimated 13% of all Macs -- for a variety of reasons, including the fact it was the newest to work on the older 32-bit hardware.

The Beta build of Chrome 64-bit for OS X can be downloaded from Google's website.