Bootable USB flash drives
If a USB flash drive or any other external drive is to be made capable of starting a computer up so that it can be used, it must have software installed that makes it able to boot the computer. Likewise, rescue DVD discs that can be created by backup/system imaging and anti-virus/malware software burn software to them that makes the discs bootable.
However, if the computer’s BIOS or UEFI BIOS has another device such as the hard disk drive containing a version of Windows set as the first boot device in the order of boot devices, Windows will boot even if a bootable flash drive or DVD disc is inserted before the computer is switched on.
To prevent that from happening, the flash drive or other external drive has to be set as the first boot device in the BIOS or new UEFI BIOS. That will probably have to be done even if there is nothing installed on the main boot hard disk drive, because the BIOS/UEFI is rarely set as the first boot device by default. If the first boot device is set as a USB device and there is not one inserted, the BIOS will discover that fact and boot from the second boot device, which is most likely to be a hard disk drive or SSD drive.
Visit the following page for information on how to change the order of boot devices in a standard BIOS:
https://www.pcbuyerbeware.co.uk/the-pccomputer-bios/6/
How to Fix Issue Booting to DVD/CD with New UEFI BIOS Boot Order –
The video linked to below deals with changing the boot order of devices on a new laptop which has a UEFI BIOS. The man wanted to boot from a DVD, but if you want to boot from a USB flash or external drive, you set the boot device to USB. He disabled the UEFI’s Secure Boot, which does not allow the system to boot from unknown media, and changed the UEFI BIOS to a standard BIOS by choosing the CSM Boot.
The man set the first boot device to his laptop’s DVD drive. The other boot-device options shown in the video are HDD/SSD (hard disk drive or solid state drive, which will boot the operating system (Windows 8.1 and 10 that use a UEFI BIOS. Windows 7 and earlier versions do not use a UEFI BIOS), USB, the one you want to set as the first boot device to boot from a flash drive, and LAN, which is booting from a home Local Area Network.
It is possible to install Windows 8/8.1 on a flash drive (or an external hard disk drive or SSD) and boot Windows from the flash drive (or external HDD/SSD).
How (and Why) to Run Portable Versions of Windows [March 2019] –
https://www.howtogeek.com/406118/how-and-why-to-run-portable-versions-of-windows/
How to run portable programs and applications from a flash drive
It is possible to run entire portable application programs from a flash drive. You can use them to work from any computer that has a USB port, save the files to your own application programs on the flash drive, and then save any documents you create to your main computer. With the new U3 standard – visit this page for information on it – https://www.everythingusb.com/software.html – it is even easier to use a flash drive as a portable computer.
List of portable software –
https://en.wikipedia.org/wiki/List_of_portable_software
Portable OpenOffice.org runs from a flash drive
It is now possible to run a full free office suite from a flash drive. You can download the Portable OpenOffice.org. It contains a word-processor, spreadsheet, database, and drawing and presentation tools. Read about it here:
Apache OpenOffice Portable –