[syslinux] Structure of VBR in FAT32?

Avi Deitcher avi at deitcher.net
Thu Jan 4 13:48:50 PST 2018

> You might want to read Wikipedia's articles about "FAT32" and "Design
of the FAT file system",

Good pointer. I spent far far too long on that page figuring out how fat32
is designed. But the reserved sectors, there is the key.

> reserved sectors

Right! Immediately after the FSIS before the FAT.And it usually is 32
sectors for fat32. Take off the VBR and the FSIS, and you have 30 untouched
sectors with which to play, or 15K. The still isn't enough for ldlinux.sys,
which appears to be around 68K, but you can get a lot more in 15K than 512


1. How much of ldlinux.sys gets loaded into the reserved sectors? Or is it
nothing, and just use the VBR?
2. When loading the VBR, it skips over the bytes reserved for boot
instruction, name, and FAT32 EBPB? Ah, right, I see it in the ldlinux.bin.
First 11 bytes are jump instruction and SYSLINUX label, then all nulls
where the EBPB would be. Nice.

Avi Deitcher
avi at deitcher.net
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