As promised at its developer conference last month, Apple today is opening the doors to prerelease versions of OS X El Capitan and iOS 9. Apple unveiled the upcoming revisions in June at its annual Apple Worldwide Developers Conference and said it would release public betas of both OSes this month.

Apple's goal with public betas is to give users a chance to preview what's coming and to submit feedback prior to the final releases expected this fall. Apple ran a similar public beta program last year for OS X Yosemite. The company also runs a separate, private beta program for its developers.

As you may expect, beta software -- even from Apple -- can be unstable, features may not work as you expect, and you may come across bugs and software incompatibilities. So take care when installing and running.

El Capitan public beta
(Credit: Apple)

Back up before you download the beta

Make sure you have a good and current backup. For iOS, archive an iOS backup with iTunes.

If you are looking at El Capitan, consider running the beta on an external hard drive or a separate partition, not on your primary Mac drive. If checking out iOS 9, look at installing the beta on a second device, not your primary one.

Unless you just can't wait to see what Apple is up to, you might find it makes more sense to wait till the fall, when the final versions are expected to ship. Read our first look at El Capitan to see what's new.

Installing and uninstalling

According to Apple, you'll be able to install the final version of El Capitan over the public beta. However, if you want to remove the beta before then, you'll need to first erase the beta software, reinstall the latest shipping version of OS X, and then restore your apps and files from the backup you thoughtfully made.

Likewise, with iOS 9, you'll be able to install the final version of iOS when it ships. If you decide to back out of the beta program ahead of the fall release, put your mobile device in recovery mode and restore it. Then you can set up your device from your archived backup.

How to get the betas

To take part, head over to Apple's beta software program page and sign up with your AppleID. After you've signed up, use your AppleID to sign in to the page.

For OS X, you should see a Download the OS X El Capitan Public Beta button and a redemption code for downloading the El Capitan beta installer from the Mac App Store. The download is big, but once it finishes, follow the onscreen instructions to complete the installation.

OS X El Capitan
Click Continue and then follow onscreen instructions to install the public beta of El Capitan.

For iOS 9 download and installation, follow the instructions on the Guide for Public Betas iOS page.

Apple says you will receive updates to the El Capitan public beta through the Mac App Store and the iOS 9 public beta through iOS Software Update.

Clifford Colby follows the Mac and Android markets for Download.com. He's been an editor at Peachpit Press and a handful of now-dead computer magazines, including MacWeek, MacUser, and Corporate Computing.