How to Create a Portable PC on a USB Drive
Now that so many of us are signed up to cloud storage services, USB drives aren't as ubiquitous as they once were, but they still have their uses. One of those uses is running an entire computer system entirely on the USB stick, which you can then bring anywhere. Your files and apps are always with you rather than being left at home or at the office, and if you're at a new desk you don't have to spend time getting everything set up the way you want—just plug in the drive, and you're up and running.
How it works
Of course you can't take an entire PC around with you on a USB stick—you need a monitor, a keyboard, a motherboard, and everything else. That said, all of the software and storage can be handled on a portable USB drive: As long as you have access to a computer with a spare USB slot, you can run your portable PC.
There's no interference with the existing setup on the computer you're using either, so you can borrow one from a colleague or a friend without causing them any hassle. You reboot the PC, tell it to load up your USB stick rather than what's on the internal drive, and your operating system appears. When you're done, shut down the computer, unplug your USB drive, and you've left no trace behind.
It's great if you're always moving between locations, and want to have access to the same desktop interface wherever you go. It can also be useful if you're trying to troubleshoot problems with your hardware setup, or if you want to try out different operating systems without installing anything permanently on your computer.
You do need to bear in mind some caveats, though. A USB drive isn't as fast or as capable as a full desktop or laptop system, so you're limited to basic computing tasks. This doesn't really work on Macs either, because of their different architecture—if you need to run a separate system on macOS, the best approach is setting up a virtual machine.
Choosing an OS
When it comes to picking an operating system for your USB PC, you can use Windows if you'd like to—via a third-party tool such as WinToUSB—though you will need a paid license for it, and the user experience isn't the best. A better idea is to go for a flavor of Linux: Not only is the software free to use, it's also more lightweight, which means you're not putting as much stress on the USB drive and everything should run more smoothly.
If you're new to Linux, it's an open source desktop OS that comes in a wide variety of flavors known as distros. It doesn't offer the same kind of broad software selection or hardware support as Windows or macOS, but all the core computing apps are covered: You can browse the web, check your email, do some work, edit images, and plenty more on Linux.
When it comes to choosing the distro you want to use, it's really up to you: Just about any version of Linux can be run fairly easily from a USB stick. Make sure you look for a feature called "persistence" in the distro documentation, though—this means you're going to be able to save settings and files to the USB drive, rather than starting up fresh with a clean slate every time you boot it up.
Ideally, you want to choose a distro that's lightweight and basic, to give you the smoothest operation possible. Puppy Linux and Linux Lite are often recommended for this particular purpose, while Tails is great if security is a priority—it automatically connects to the Tor network when you go online. Ubuntu is an excellent choice too, offering a polished interface and plenty of help documentation.
Getting started
Head to the official website for your Linux distro of choice, then look for an ISO download—this is essentially the operating system in its entirety. Downloads like this can often run to several gigabytes in size, so you might have to wait a while. It's also worth checking in the distro's documentation to see if there are any notes or recommendations regarding USB installation.
Next, you need a program to put the ISO on the USB drive for you—not just to copy over the file, but to make the drive bootable. There are a few options here, including Rufus, but we've gone for Etcher for this guide: It's really simple to use, and you can run it on both Windows and macOS (and, indeed, Linux).
Fire up Etcher, and you'll see there are three stages: Pick Flash from file to pick the ISO from disk, then Select target to choose a USB drive connected to your computer, and then click Flash to complete the operation. As far as USB drives go, a capacity of at least 8GB is recommended, plus the fastest read/write speeds you can find—you might find more requirements listed on the pages of the distro you've chosen.
With all that taken care of, you can use your USB drive by putting it in a spare USB port on any computer, then restarting the computer and choosing to boot from the USB stick. How this is done varies, but it usually involves pressing a key to choose a boot device while the computer's starting up—look for a message on screen or check the documentation that came with the computer, if you're not sure.