> ## Documentation Index
> Fetch the complete documentation index at: https://docs.ryoku.dev/llms.txt
> Use this file to discover all available pages before exploring further.

# Dual-boot with Windows

> Install Ryoku alongside Windows on one disk. Make free space first, then pick "Install alongside" — the installer reuses your EFI partition and never touches Windows.

Ryoku installs alongside Windows on a single disk. The installer **reuses the
existing EFI partition** and drops Ryoku into **free (unallocated) space** — it
never resizes, moves, or erases your Windows partition. Because of that, you make
the room first, then run the installer.

<Info>
  **The one thing that trips people up:** Ryoku does not shrink Windows for you.
  If Windows fills the whole disk, there is no free space for Ryoku, and the
  installer's **Disk layout** step will not let you continue (Tab does nothing)
  until you free some space. Do [Step 1](#step-1%3A-make-room-in-windows) first.
</Info>

## What you need

Dual-boot alongside Windows requires all of these:

* **UEFI + GPT.** Boot the Ryoku USB in UEFI mode (not BIOS/CSM/legacy). A UEFI
  Windows install already uses GPT and has an EFI System Partition (ESP).
* **An existing EFI partition** to reuse — a UEFI Windows install has one.
* **Enough unallocated free space** for Ryoku: at least **15 GiB for the root**
  plus **your swap size** (the default swap is 16 GiB, so \~31 GiB; 64 GiB or more
  is comfortable). Ryoku and the Windows boot manager then share the one ESP.

No second disk is required. (If you would rather keep the two systems fully
separate, put Ryoku on a dedicated drive and choose **Erase whole disk** instead.)

## Step 1: Make room in Windows

Do this from **Windows**, before booting the installer.

<Steps>
  <Step title="Turn off Fast Startup and BitLocker">
    Fast Startup leaves the Windows filesystem in a hibernated state, which can
    corrupt data when another OS touches the disk. Turn it off: **Control Panel →
    Power Options → Choose what the power buttons do → uncheck "Turn on fast
    startup"**. If BitLocker is on, suspend or disable it first (and save your
    recovery key).
  </Step>

  <Step title="Shrink the Windows partition">
    Press `Win + X` → **Disk Management**. Right-click your Windows (C:) volume →
    **Shrink Volume**, and shrink it by at least the space Ryoku needs (aim for
    **64000 MB / 64 GiB** or more). This leaves **Unallocated** space after the
    Windows partition — that is where Ryoku goes.
  </Step>

  <Step title="Fully shut down Windows">
    Use **Shut down** (not Restart, not Sleep) so the disk is left clean.
  </Step>
</Steps>

## Step 2: Disable Secure Boot

Reboot into your firmware setup (usually `F2`, `Del`, or `F12` at power-on) and
turn **Secure Boot off**. Save and exit. See [Install Ryoku](/docs/install) for
the full pre-install checklist and how to write the USB.

## Step 3: Install alongside Windows

Boot the Ryoku USB in **UEFI mode**. In the installer:

<Steps>
  <Step title="Pick the target disk">
    At **Target disk**, choose the disk that holds Windows.
  </Step>

  <Step title="Choose the alongside strategy">
    At **Disk strategy**, pick **Install alongside Windows** (it is the first,
    default option). Nothing is written until the final Review step.
  </Step>

  <Step title="Confirm the layout, then press Tab">
    The **Disk layout** step shows your disk: the kept Windows and EFI
    partitions, and a new Ryoku root in the free space. Adjust swap if you like,
    then press **Tab** to continue to Review. Confirm on Review to install.
  </Step>
</Steps>

Ryoku reuses the existing EFI partition, creates its root in the free region, and
installs the Limine bootloader with an entry for Windows, so both systems show up
at boot.

## "I press Tab and nothing happens"

On the **Disk layout** step, Tab only continues once the alongside layout is
actually installable. When it is blocked, the screen shows a red `⚠` line with
the reason. The usual causes:

<AccordionGroup>
  <Accordion title="Not enough free space (the most common one)">
    Windows is using the whole disk, so there is no room for Ryoku. Go back to
    [Step 1](#step-1%3A-make-room-in-windows) and shrink the Windows partition to
    leave at least 15 GiB plus your swap size of unallocated space, then reboot
    into the installer. (Or press `esc` and choose **Erase whole disk** on a
    dedicated drive.)
  </Accordion>

  <Accordion title="No EFI partition to reuse">
    The installer found no EFI System Partition on the disk. This happens when
    Windows was installed in **legacy/BIOS (MBR)** mode instead of UEFI, or when
    you booted the USB in BIOS mode. Reinstall/boot in UEFI mode, or press `esc`
    and choose **Erase whole disk**.
  </Accordion>

  <Accordion title="The disk is smaller than 32 GiB">
    Ryoku needs at least 32 GiB total. Pick a larger disk.
  </Accordion>
</AccordionGroup>

<Tip>
  This is expected, not a bug: `Install alongside Windows` is intentionally
  non-destructive, so it refuses to continue rather than guess where to put
  Ryoku. Once there is a reusable ESP and enough free space, Tab advances.
</Tip>

## After install

The Limine boot menu appears at power-on with entries for **Ryoku** and
**Windows** — pick whichever you want. If Windows does not appear, boot Ryoku and
run `ryoku doctor`, then see [Troubleshoot](/docs/troubleshoot).

## See also

<CardGroup cols={2}>
  <Card title="Install Ryoku" icon="download" href="/docs/install">
    The full install walkthrough, from ISO to first boot.
  </Card>

  <Card title="Troubleshoot" icon="wrench" href="/docs/troubleshoot">
    Boot, login, and disk recovery when something goes wrong.
  </Card>
</CardGroup>