Interrupt 19 Capture is a BIOS setting that allows add-on storage controllers (like RAID cards, SCSI adapters, or network boot cards) to take over the boot process so your computer can start up from drives connected to those controllers. If you’ve spotted this option in your BIOS setup, it’s there because your motherboard has detected a host adapter with its own ROM that needs permission to intercept the normal boot sequence.
How the Boot Process Normally Works
When your computer finishes its power-on self-test (POST), the BIOS triggers a software routine called Interrupt 19h. This is the bootstrap loader: its sole job is to find a bootable disk, load the first sector of that disk into memory, and hand off control to whatever operating system lives there. On a basic system with drives plugged directly into the motherboard, Interrupt 19h knows exactly where to look because those drives are visible to the BIOS natively.
The problem arises when you install an expansion card, like a RAID controller or a network adapter, that has its own drives or boot sources attached. The motherboard BIOS has no built-in knowledge of those devices. It can’t boot from a RAID array it doesn’t understand. That’s where Interrupt 19 Capture comes in.
What “Capturing” the Interrupt Means
Each expansion card with bootable devices carries a small firmware chip called an option ROM. When Interrupt 19 Capture is enabled, the option ROM on that card is allowed to “hook” the Interrupt 19h call. Hooking means the card inserts itself into the boot chain: it saves a pointer to the original Interrupt 19h handler, then replaces it with its own boot loader. When the BIOS fires Interrupt 19h, the card’s boot loader runs first.
If the card successfully finds a bootable operating system on one of its attached drives, it loads and runs it. If the boot attempt fails, the card passes control back to the original Interrupt 19h handler, allowing the system to fall back to another boot device. This fallback design means capturing the interrupt doesn’t permanently block other boot options; it simply gives the expansion card first priority.
When You Need It Enabled
You should enable Interrupt 19 Capture if you’re booting your operating system from a drive connected to an add-on controller rather than the motherboard’s built-in ports. Common scenarios include:
- Hardware RAID controllers: If your OS lives on a RAID array managed by a dedicated card, that card must capture Interrupt 19 to present the array as a bootable volume.
- SCSI or SAS host adapters: Drives on these controllers aren’t visible to the standard BIOS boot loader without the option ROM stepping in.
- Network boot adapters: PXE boot cards hook Interrupt 19h so they can attempt a network boot before any local disk is tried.
When this setting is disabled, the option ROM on the host adapter cannot intercept the boot sequence. The BIOS will only try to boot from devices it natively recognizes, typically drives on the motherboard’s own SATA or NVMe ports. If your only bootable OS is on a RAID card and you disable this setting, the system won’t find an operating system.
Potential Boot Problems
Interrupt 19 Capture is straightforward with a single expansion card, but complications arise when multiple cards try to hook the same interrupt. The BIOS Boot Specification (authored by Compaq, Phoenix, and Intel) documents several failure modes. A “legacy” card that hooks Interrupt 19h during its initialization takes full control of the boot process, potentially locking out other devices. If a card hooks Interrupt 18h (the boot failure handler), the normal recovery path breaks entirely, meaning the system can’t gracefully try another boot device if the first one fails.
In the worst case, a failed boot attempt from a card that captured Interrupt 19h can hang the system. The specification notes that a device that fails to boot “may display an error message and never return control to the BIOS.” This is why the boot spec requires well-behaved devices to clean up any memory modifications and invoke the failure handler so control returns to the BIOS for the next boot option.
If you’re troubleshooting a system that freezes during boot or skips your intended boot drive, check whether Interrupt 19 Capture is set correctly. Enabling it when no expansion card needs it is harmless on most systems, but disabling it when a card does need it will prevent that card’s drives from appearing as boot candidates.
Interrupt 19 Capture on Modern Systems
This setting belongs to the legacy BIOS world. Systems running UEFI firmware handle the boot process differently, using their own boot manager and device drivers instead of software interrupts. However, many UEFI motherboards include a Compatibility Support Module (CSM) that emulates the old BIOS environment for legacy operating systems or older expansion cards. When CSM is active, the UEFI firmware still fires Interrupt 19h just before handing off to a legacy boot option, and the capture mechanism works the same way it always has.
If your system is configured for pure UEFI booting with CSM disabled, the Interrupt 19 Capture setting either won’t appear in your BIOS menus or will have no effect. Modern RAID controllers and network adapters include UEFI-compatible drivers that register directly with the UEFI boot manager, eliminating the need to hook an interrupt vector.
Practical Guidance
If you’re running a standard desktop with drives connected to the motherboard, you can safely leave Interrupt 19 Capture disabled or ignore it. The setting only matters when an expansion card with its own firmware needs to participate in booting. For servers or workstations with dedicated RAID or SCSI controllers, enable it. And if you’re using UEFI boot mode without CSM, the setting is a relic that no longer applies to your configuration.