Installing Ubuntu alongside Windows lets you use both operating systems on the same PC without replacing your existing Windows installation. The part that requires the most care is not creating the USB installer—it is preparing the disk and choosing the correct installation option.

This guide walks through a typical UEFI/GPT dual-boot setup, from preparing Windows to selecting an operating system after installation. It is based on my earlier installation notes, with the guidance updated against current Ubuntu and Microsoft documentation. The steps are not a report of a newly tested installation on a specific PC; exact screens and available options depend on the Ubuntu release and hardware.

0. Before You Begin

You will need:

  • A Windows PC using UEFI firmware and a GPT-partitioned disk.
  • Enough free storage for Ubuntu. Ubuntu lists 25 GB as a minimum; 50 GB or more is a more practical target if you plan to install applications and development tools.
  • An 8 GB or larger USB flash drive. Its existing contents will be erased.
  • A backup of your important files, preferably on external storage.
  • Administrator access to Windows and, if necessary, the firmware settings.

This article uses Ubuntu Desktop 26.04 LTS as the current reference release. Ubuntu 24.04 LTS, mentioned in my original 2025 notes, uses a similar general workflow, but installer screens and disk-encryption options can differ. The Windows instructions are primarily for Windows 11. Windows 10 can follow a similar process, but its standard support ended on October 14, 2025; continuing to use it requires an appropriate support or migration plan.

Important: Partition changes and operating-system installation carry a risk of data loss. Do not proceed unless you have verified your backup. If the installer does not clearly identify your Windows installation and the intended destination disk, stop rather than guessing.

Confirm that Windows uses UEFI

In Windows, press Win + R, enter msinfo32, and check BIOS Mode in System Information. For the workflow below, it should say UEFI. You can inspect the disk's partition style in Disk Management or the disk's Properties → Volumes tab.

Legacy BIOS/MBR systems require different instructions. Do not change a working Windows installation from Legacy BIOS to UEFI or convert its partition table just to follow this guide.

Understand Secure Boot and BitLocker

Secure Boot: Ubuntu supports UEFI Secure Boot on standard supported hardware. You generally do not need to disable it before installing Ubuntu. If you encounter a specific boot or third-party-driver problem, investigate that problem before changing firmware security settings.

BitLocker / Device Encryption: First, check whether Windows drive encryption is enabled and save your recovery key somewhere you can access even if Windows will not boot. Changing the boot configuration can trigger a BitLocker recovery prompt.

BitLocker requires special attention because suspending protection is not the same as turning off BitLocker and decrypting the drive. In some cases the Ubuntu installer cannot safely resize or inspect an encrypted Windows partition. Ubuntu 25.04 and later improved support for installing alongside existing BitLocker partitions when suitable space is available, but that does not mean every BitLocker layout is supported. If the installer explicitly requires BitLocker to be disabled, return to Windows and follow Ubuntu's BitLocker guidance rather than forcing the installation. Check that your Windows edition allows you to turn encryption back on before decrypting.

1. Prepare Windows

1.1 Back up your files

Copy important documents and project files to an external drive or a trusted backup location. If available, create Windows recovery media or a system image as well. Confirm that you can actually read the backup before changing partitions.

1.2 Disable Fast Startup

Windows Fast Startup uses a form of hibernation, which can leave Windows filesystems in a state that is unsafe to modify from another operating system.

On systems that expose this option:

  1. Open Control Panel → Hardware and Sound → Power Options.
  2. Select Choose what the power buttons do.
  3. Select Change settings that are currently unavailable.
  4. Clear Turn on fast startup, then save the changes.

The option may be absent on some PCs. Also avoid leaving Windows in hibernation when switching to Ubuntu, especially if you intend to access Windows partitions from Linux.

1.3 Check BitLocker before resizing the disk

If Windows encryption is enabled, make sure the recovery key is securely backed up before changing disk or boot settings. Whether encryption needs to be disabled depends on the operation and on what the installer supports.

Do not assume that clicking Suspend protection decrypts the disk. If the Ubuntu installer specifically requires the Windows drive to be decrypted, follow the documented Turn off BitLocker procedure, let decryption finish, and verify that Windows still starts correctly before trying again.

1.4 Create unallocated space for Ubuntu

  1. Press Win + X and open Disk Management.
  2. Locate the Windows partition, typically C:. Confirm the disk and partition carefully.
  3. Right-click the partition and select Shrink Volume.
  4. Enter the amount of space you want to allocate to Ubuntu.
  5. Complete the operation and verify that the disk shows Unallocated space.

Leave that space unallocated. Do not create a new NTFS volume for Ubuntu. Also do not delete or format the EFI System Partition (ESP), Windows recovery partitions, or other existing partitions.

The installer may also be able to resize a Windows partition itself. Preparing unallocated space from Windows makes it easier to identify the intended destination during installation, but the exact available installation options still depend on the disk layout.

2. Create an Ubuntu Installation USB in Windows

2.1 Download Ubuntu Desktop

Download the Ubuntu Desktop ISO from the official Ubuntu download page. For a typical Intel or AMD Windows PC, select the appropriate 64-bit x86 (amd64) Desktop image.

2.2 Write the ISO to a USB drive with Rufus

  1. Insert an 8 GB or larger USB drive. Its contents will be erased.
  2. Download Rufus and launch it on Windows.
  3. In Device, select the correct USB drive.
  4. Under Boot selection, select the Ubuntu ISO.
  5. For a modern UEFI system, Rufus's defaults are usually appropriate. If the USB does not boot, Ubuntu's documentation suggests trying GPT as the partition scheme and UEFI (non CSM) as the target system.
  6. Click START and confirm that you want to overwrite the USB drive.
  7. Wait until Rufus reports that it is ready.

Simply copying the .iso file onto a USB drive does not create a bootable installer. See Ubuntu's USB creation guide for screenshots and additional details.

3. Boot from the Installation USB

  1. Leave the USB installer connected and restart the PC.
  2. Open the one-time firmware boot menu. Depending on the manufacturer, the key may be F12, Esc, F2, or F10.
  3. Select the USB boot entry, preferably the one explicitly marked UEFI if multiple entries appear.
  4. Allow the Ubuntu installer to start.

Using the one-time boot menu is preferable to permanently changing the firmware boot order just to launch the installer.

If the Ubuntu live environment offers Try Ubuntu, you can use it to check basic hardware compatibility—display, Wi-Fi, keyboard, and storage detection—before installing. Return to the installer when ready.

4. Install Ubuntu Alongside Windows

Follow the Ubuntu Desktop installer prompts for language, keyboard, network, and software options until you reach Disk setup (the exact wording varies by release).

4.1 Recommended: Install Ubuntu alongside Windows

If the installer recognizes the existing Windows installation and offers an option similar to Install Ubuntu alongside Windows Boot Manager:

  1. Select the alongside option—not Erase disk and install Ubuntu.
  2. Confirm the destination drive and the storage allocation proposed for Ubuntu.
  3. Review the summary of partition changes before confirming.
  4. Continue only if the summary clearly preserves the Windows installation and uses the intended space.

This is usually the simplest route. Depending on the release and disk layout, the installer may resize an existing partition or use available space.

Danger: Erase disk and install Ubuntu is not the correct option when you want to keep Windows on that same disk. It can destroy the existing Windows partitions and data.

4.2 If the alongside option is missing

Do not select Erase disk as a workaround. First check whether the installer detects the correct storage drive and whether encryption or storage-controller settings are preventing Windows from being recognized.

The current installer calls the advanced option Manual partitioning; older tutorials may call it Something else. Manual partitioning is for users who are comfortable identifying disks and partitions. A typical arrangement on an existing UEFI/GPT Windows disk is:

Existing or new partition Intended handling
Windows partitions Keep unchanged; do not format
Existing EFI System Partition (ESP) Reuse as required by the installer; do not format
Ubuntu root (/) Create an ext4 filesystem in the intended unallocated space

On a normal single-disk UEFI installation, an ESP usually already exists. You generally do not need to create another one. The precise EFI mount-point and bootloader controls differ across Ubuntu installer versions; follow the interface for your release instead of assuming an old screenshot or a specific /dev/nvme... device name applies.

If you cannot positively identify every partition involved, cancel the installation and inspect the disk layout from Windows before proceeding.

4.3 If storage or encryption causes an installer warning

  • BitLocker warning: Refer to the official BitLocker installation guidance. Installing next to an encrypted Windows system is possible only when the installer can handle the specific disk layout.
  • Intel RST / RAID warning: Review Ubuntu's Intel RST guidance. Do not casually switch RST/RAID to AHCI in firmware: Windows may stop booting, and RAID changes may make data inaccessible.
  • Windows not detected: Stop and verify the boot mode, disk layout, encryption status, and storage-controller configuration. Do not assume the installer has found the correct drive merely because it offers unused space.

5. Restart and Choose Your Operating System

After installation finishes:

  1. Restart when the installer prompts you.
  2. Remove the installation USB when requested.
  3. If the GRUB menu appears, select Ubuntu or Windows Boot Manager.
  4. Boot into both systems at least once to confirm they work.

On some systems the GRUB menu may be hidden or the firmware may boot directly into one OS. This does not automatically mean that the other operating system was deleted.

If the PC always launches Windows, inspect the UEFI boot menu / boot order for an ubuntu entry. If it exists, selecting it may start Ubuntu. Avoid modifying or deleting Windows Boot Manager entries without understanding the configuration.

If Windows does not appear in GRUB, confirm first whether it remains available in the firmware boot menu. GRUB menu contents depend on the installed configuration, and a missing menu entry is not by itself proof of a damaged Windows partition.

6. After Installation

Update Ubuntu

Open a terminal in Ubuntu and run:

sudo apt update sudo apt upgrade

Reboot if the updates require it, and check that the machine can still start both operating systems.

Verify Windows and drive encryption

Boot Windows and confirm that your files and applications are available. If you temporarily suspended BitLocker protection, verify that it has resumed. If you turned off BitLocker and decrypted the drive, decide whether to re-enable encryption based on the capabilities of your Windows edition and your security requirements.

Keep the BitLocker recovery key accessible even after installation. Bootloader, firmware, and security-setting changes may trigger recovery later.

Final Checklist

Before considering the installation complete, verify that:

  • [ ] Important Windows files are backed up and accessible.
  • [ ] Windows and Ubuntu both boot successfully.
  • [ ] The Ubuntu installation uses only the intended disk space.
  • [ ] The Windows EFI and recovery partitions were not accidentally formatted.
  • [ ] BitLocker/Device Encryption is in the state you intended, and recovery keys are stored safely.
  • [ ] Ubuntu software updates have been applied.

Dual-boot installations are usually straightforward when the installer correctly identifies Windows and offers a guided alongside option. The main rule is to stop when disk or encryption information is ambiguous rather than trying to force the installer to continue.

References

AI disclosure: This article documents my own technical setup and results. An LLM was used to help draft, organize, and edit the English text. I remain responsible for its technical accuracy.