An ISO file is an image of installation media. It is not a normal hard-disk file system you install by simply leaving it on the disk. To install an operating system from it, you usually either write it to bootable USB/DVD media or attach it to a virtual machine as a virtual optical disk.
Prepare before you write or boot the ISO
- Confirm the exact operating system, version, edition, and CPU architecture. For example, a Windows or Linux ISO for one edition or architecture may not match your license, hardware, or VM settings.
- Check the official hardware requirements for that exact OS. Do not assume every computer supports Windows 11 or a current Linux release.
- Back up the target machine and identify the disk you intend to erase or keep.
- Decide whether you are installing on a physical computer or inside a virtual machine; the steps and risk are different.
First decide whether the ISO is trustworthy
Only use ISO files from the operating-system vendor or project. If an ISO is untrusted, do not run it on your physical computer and do not treat a virtual machine as a trust guarantee. A VM can reduce the risk of changing your physical partitions, but it does not make unknown software safe. If the project provides hashes or signatures, verify them first; Ubuntu’s download verification guide explains checking ISO integrity and authenticity with SHA256 and GPG files.
Path A: install on a real computer from USB
For Windows, Microsoft’s installation media guide says a USB flash drive can be used to install, clean install, or reinstall Windows, and an ISO can be made for VMs or DVD. For Ubuntu, the Ubuntu Desktop install guide says the ISO must be written to a USB stick; copying the ISO file is not enough, and the USB stick will be erased.
- Back up the target computer and the USB drive.
- Use the OS vendor’s media tool or a reputable image writer to write the ISO to the USB drive.
- Restart the target computer and open its boot menu, often with F12, Esc, F8, or a vendor-specific key.
- Select the USB device, not the internal hard disk.
- When the installer asks where to install, choose the intended target disk carefully. This is the step that can erase data.
- After installation finishes and the computer restarts, remove the USB if the system keeps returning to the installer.
Menu names vary by Windows, Ubuntu, firmware, and hardware vendor. Follow the wording for your exact version, but keep the same safety rule: verify the ISO, choose the correct boot device, and choose the correct target disk.
Path B: install in VirtualBox
If you want to test or learn without changing physical partitions, create a VM and attach the ISO to that VM. This protects the host disk from accidental OS installation, but it does not prove the ISO is safe.
- Open VirtualBox and click New.
- Choose the OS type and version that matches the ISO as closely as possible. If menus differ by VirtualBox version, choose the closest equivalent.
- Assign memory within your host’s capacity; do not starve the host OS.
- Create a new virtual hard disk for the VM.
- Open the VM settings and attach the ISO to the virtual optical drive, or choose the ISO when VirtualBox asks for a startup disk.
- Start the VM and follow the installer. When asked for an install target, select the VM’s virtual disk, not a host disk passthrough device.
- After installation, shut down or reboot the VM and eject/remove the ISO from the virtual optical drive. Otherwise the VM may boot back into the installer again.
What about mounting the ISO in the current OS?
Mounting an ISO with a virtual optical drive lets you see files or start an in-place setup from a running system. It is useful for upgrades or reading files, but it is not the same as booting a blank computer from installation media. For a clean installation, boot from USB/DVD or boot the VM from the attached ISO.