How to Disable CSM in BIOS/UEFI Setup (And When You Should)
If you've ever tried to install Windows 11, enable Secure Boot, or use a modern NVMe drive, you may have run into a setting called CSM — and been told to turn it off. Here's what it actually does, why disabling it matters, and what changes when you do.
What Is CSM and Why Does It Exist?
CSM stands for Compatibility Support Module. It's a component built into your motherboard's UEFI firmware that emulates the older BIOS (Basic Input/Output System) environment. BIOS was the standard firmware interface for PCs for decades before UEFI replaced it.
The problem is that not everything made the jump cleanly. Older operating systems, bootloaders, GPT/MBR disk configurations, and some older hardware expect the legacy BIOS environment to be present. CSM bridges that gap — it lets a modern UEFI motherboard still boot and run older software and OS installations that were built around legacy BIOS assumptions.
When CSM is enabled, your system can boot from MBR (Master Boot Record) disks and supports legacy option ROMs for older expansion cards. When it's disabled, your system runs in pure UEFI mode, which is required for features like Secure Boot, TPM 2.0 enforcement, and fast boot from GPT-formatted drives.
Why You Might Need to Disable CSM
Several modern requirements specifically depend on CSM being off:
- Windows 11 installation requires Secure Boot and TPM 2.0 to be active. Secure Boot cannot function properly while CSM is enabled on most systems.
- NVMe boot drives perform best — and sometimes only boot correctly — in pure UEFI mode.
- GPT disk partitioning, the modern replacement for MBR, is fully supported in UEFI mode without CSM interference.
- Some GPU drivers and resizable BAR (ReBAR) features require CSM to be disabled to work correctly.
Essentially, if you're running modern hardware and a current operating system, CSM is a legacy compatibility layer you probably no longer need. 🖥️
How to Disable CSM: General Steps
The exact process varies by motherboard manufacturer, but the general path is consistent across most systems.
Step 1: Enter Your UEFI Setup
Restart your PC and press the key to enter firmware setup during POST. Common keys include:
| Manufacturer | Common Setup Key |
|---|---|
| ASUS | Del or F2 |
| MSI | Del |
| Gigabyte | Del or F2 |
| ASRock | F2 or Del |
| HP | F10 or Esc |
| Dell | F2 |
| Lenovo | F1, F2, or Enter |
Step 2: Locate the CSM Setting
Once inside the UEFI, look for CSM under one of these sections depending on your firmware:
- Boot tab → Boot Configuration or Boot Mode
- Advanced tab → CSM Configuration
- Security tab (on some OEM systems)
The setting may be labeled "CSM Support," "CSM/UEFI Boot Mode," or simply "Launch CSM."
Step 3: Disable CSM
Change the value to Disabled or UEFI Only. Some boards give you granular options for CSM behavior across different device types (storage, video, PCIe). If available, set all sub-options to UEFI before disabling the main CSM toggle.
Step 4: Enable Secure Boot (If Needed)
If your goal is Secure Boot or Windows 11 compatibility, this is the moment to enable it. With CSM off, Secure Boot should now be available in your firmware's Security or Boot section. You may also need to clear or configure Secure Boot keys — most boards offer a "Set Factory Defaults" or "Restore Secure Boot Keys" option to make this straightforward.
Step 5: Save and Exit
Save changes (usually F10) and restart.
What Can Break When You Disable CSM ⚠️
This is where individual setups diverge significantly.
If your OS was installed in legacy BIOS mode (on an MBR disk), disabling CSM will likely cause your system to fail to boot. You'd need to either convert your installation from MBR to GPT (Windows has a tool called mbr2gpt for this) or reinstall the OS in UEFI mode.
Older GPUs with legacy option ROMs may display nothing until the OS loads its driver — meaning you lose the boot screen visibility, though the system still functions.
Older PCIe expansion cards (network cards, RAID controllers) that rely on legacy option ROMs may not initialize correctly without CSM.
Dual-boot setups with older Linux distributions or other operating systems installed in legacy mode can become unbootable.
The Variables That Make This Different for Every System
Whether disabling CSM is straightforward or complicated depends on a combination of factors:
- How your current OS was installed — UEFI mode or legacy BIOS mode determines whether your existing boot will survive the change
- Your disk partition style — GPT or MBR, which you can check in Windows Disk Management
- Your GPU's age and firmware — newer cards handle pure UEFI fine; some older cards don't
- Your motherboard generation — newer boards handle CSM removal cleanly; older firmware implementations can be quirky
- Whether you run any legacy hardware — older PCIe cards, certain network adapters, or specialized hardware may depend on CSM
A user on a brand-new build installing Windows 11 fresh will have a nearly frictionless experience turning CSM off. A user with a years-old Windows 10 installation on an MBR drive, a legacy GPU, and mixed-age hardware faces a meaningfully different situation — one where the same toggle flip has significantly more downstream consequences.
The setting itself is simple. What sits behind it — your disk format, your OS installation mode, your hardware inventory, and what you actually need the system to do — is what determines whether disabling CSM is a two-minute task or a careful migration. 🔧