Comment 7 for bug 1706296

This workaround should help you avoid problems with Windows NT 4.0.

Create the disk image for the hard drive that is 4GB or less in size:
qemu-img create -f qcow2 <HD image file name>.qcow2 4G

Run QEMU booting from the CD-ROM. I assume you used the Windows NT 4.0 workstation CD.
qemu-system-i386 -cpu pentium -vga cirrus -hda <HD image file name>.qcow2 -cdrom <path to iso> -boot c

Note: I used QEMU 2.10 RC3, Commit 1f296733876434118fd766cfef5eb6f29ecab6a8. I know the boot arguments says it will boot from the hard drive but it will still work. The BIOS will see the hard drive can't be booted and will look for another boot device. After the initial install of Windows NT 4.0 you will be required to reboot to continue with more installation. The above command-line allows you to continue with installation without having to quit QEMU. If you choose to use an older version of QEMU you may run into more problems. For example under QEMU 2.8.0 Windows NT 4.0 will think the hard drive is twice the size it really is. This will lead to an unbootable installation.