My 3 year old Lenovo T510 has legacy bios only, no UEFI.

I have read reports that stated gpt lilo incompatibility.

Using a Patriot XT Rage 32GB USB 3.0 FD (in a 2.0 socket), I performed this test.

Partitions were originally created by fdisk in the MBR scheme.

Partitions all primary linux type 83 formatted ext4
1 10GB sandbox
2 10GB data
3 5GB Slackware64 v14.1

With gdisk, I changed partition 1 type 8300 to ef02 and wrote a new GPT on the drive. There were no errors shown. (I did NOT set the bootable flag.)

Mounted the FD and executed lilo -r /mnt/sdb3; again, no errors.

Unmounted all and rebooted into the FD (not my SSD). In a few seconds there was a perfectly functioning Slackware system; no errors whatsoever.

UNIX systems have all actually supported GPT with BIOS booting for quite some time now.

The only exception has been to getting full GPT support has been Windows which still ONLY supports GPT booting with UEFI only, not BIOS, much to the headache of many users.

The Slackware64 v14.1 optical media installer uses an el-torito-altboot image generated by grub-mkimage and standard loopback techniques.

Would it be possible to use an efi-stub-enabled kernel instead? (bzImage -> bootx64.efi -> efiboot.img all placed in the usual default locations.) And, yes, I realize that there will be no menu on boot!

I do not have a UEFI capable machine (yet) to perform the test. So ...

Has anybody tried this tangent?

I can see one possible problem. The Slackware64 image (efiboot.img) is 1.44MB, the size of a "floppy". Is this a max limit dictated by the el-torito specs? A normal kernel, even xz|lzma compressed, is larger.