Installing the Mac operating system on an external drive is the safest way to get a good look at a new OS without changing anything on your Mac. You'll want to use a fast drive if you can - it's worth investing in a USB C or Thunderbolt 3 drive as this will offer the fastest connection. If not, at least make sure that you opt for flash storage.
Usually, when you want to connect an external hard drive to your computer, you just plug it in and that's it. However, if you are using a Macbook. If you want to insure full Mac compatibility of a new external hard drive or flash disk, you'll want to format the drive to the Mac OS Extended.
That drive will need at least 12GB of space, but more is recommended, in fact back when we started running Mojave beta on a 32GB stick we found it wasn't enough once we started using iCloud Desktop and other features that meant that our data started being downloaded. For buying advice, take a look at our guide to the best external drives for Mac. Your Mac will search for the latest software before offering to download it.
Alternatively, you could click on this link to be taken to the Catalina page on the Mac App Store. If you have a NAS drive that connects over the network then you should read this article about connecting to a NAS drive.
But this only works if your Mac is always connected to the external drive. Shop Now. To avoid the external drive being accessed during the recovery process, click Extras next to the drive or drive partition or file, then select Remount Volume As Read Only. The time the format takes will vary depending on the size of the drive. Tom Nelson has written hundreds of articles, tutorials, and reviews for Other World Computing and About. Now, please check your email.
There are a number of reasons why the hard drive, flash drive or SSD might not be showing up. It may have been formatted incorrectly, it may be corrupted, it may have a faulty or inadequate cable, or there could be something else. If you run though the following steps you should hopefully be able to identify the cause and fix the problem.
To unmount your drive you can right-click control-click on the icon on the Desktop or in the Finder and choose Eject. Apparently most drive issues are caused when the disk is removed without ejecting it properly.