64-bit 1.3.3.2 — Bootice

While this version is pre-Grub2-full-integration, you can still use it to chainload:

Each partition has its own PBR. BootICE allows you to modify the PBR for specific file systems:

This is essential for fixing “NTLDR is missing” or “Bootmgr is compressed” errors. bootice 64-bit 1.3.3.2

Executing bootice_x64.exe on Windows 10 22H2 (with Real-Time Protection enabled) reveals a stability flaw. The tool uses both 32-bit dialog resources (due to legacy code) and 64-bit ring-3 write operations.

Observation: When applying a new MBR code (e.g., "Windows NT 6.x MBR"), BootICE performs the following sequence: This is essential for fixing “NTLDR is missing”

However, Windows Defender’s Antimalware service intercepts step 2, performing a real-time scan of the raw disk write buffer. If the system is under load, the FSCTL_DISMOUNT_VOLUME call occasionally fails, leaving the volume locked. This results in the GUI hanging on "Updating boot code... 100%" while the disk is inaccessible until process termination.

Workaround (Found in user forums): Disabling "Real-time protection" temporarily. This is not a bug, but an emergent property of antivirus intercepting legacy disk I/O. On the Utilities tab:

When launched, the main window has several tabs:
Physical Disk | Partition Boot Record | BCD | GRUB4DOS | Utilities

On the Utilities tab: