A "portable" installation of Unity allows you to run the editor from an external drive (like a high-speed SSD) without being tied to a single machine's internal storage
Here are some tips and considerations to keep in mind when using a portable installation of Unity: unity portable install top
Result: When you plug the drive into any Windows PC (as drive U:), Unity will think these caches are on the system drive, but they are physically on your SSD. Speed is preserved, and you don't fill up the host PC's storage. A "portable" installation of Unity allows you to
You can make Unity portable if you copy it's contents onto your usb drive. If you just want to code your stuff where ever you are, Unity Discussions Download Unity Personal: Get Unity for Free Optional: Linux portable installs
A scan of the first page of Google/Bing for "unity portable install top" shows: