I have a USB but not a micro SD card. I installed the operating system onto it.
Can I use that as the storage and OS layer for my Raspberry Pi 4?
Stack Exchange network consists of 181 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.Visit Stack Exchange
Raspberry Pi Stack Exchange is a question and answer site for users and developers of hardware and software for Raspberry Pi. It only takes a minute to sign up.Sign up to join this community
Since you have a Raspberry Pi 4 it is possible to get it to boot from USB.
The process to switch from SD card boot to USB boot is demanding that you FIRST boot from a SD card.
So YES you need a SD card.
The process is roughly:
Create a bootable SD card with "Raspberry Pi OS"
Edit the /etc/default/rpi-eeprom-update
Install the bootloader update (That have the USB boot capability)
Create a bootable USB media
Now you can boot your Raspberry Pi 4 from the USB.
A more detailed description can be found here: https://www.tomshardware.com/how-to/boot-raspberry-pi-4-usb
bootcode.binon it, the rest of the boot CAN be from USB device .... Pi 3 (not +) needs to boot from SD at least once, then you need to set a "flag", and you can boot from USB from then on ...3B+ or 3A+ can boot from USB as factory default (it has the aforementioned flag pre-set) ... pi4 needs to boot from SD at least once so you can update the EEPROM bootloader to the latest "stable" version