looks like it might rhyme with:
https://doxygen.reactos.org/d7/d4a/structtagDISKCONTEXT.html
but definitely not in the same order (and DISKCONTEXT doesn't store the #bits per sector that this does:
(watched it count:
)8071e9bc: 28 89 00 01 cmplwi cr1,r9,1
8071e9c0: 41 86 00 14 beq- cr1,number of bits in sector size in 807b0074
Counting bits in sector size into r9:
8071e9c4: 39 2a 00 01 addi r9,r10,1
8071e9c8: 28 89 00 20 cmplwi cr1,r9,32
8071e9cc: 91 3e 00 14 stw r9,20(r30)
8071e9d0: 41 84 ff dc blt+ cr1,8071e9ac
number of bits in sector size in 807b0074:
8071e9d4: 81 7c 00 00 lwz r11,0(r28)
0x807b0060 00000010 00000010 00000000 00000800 ................
0x807b0070 00000600 09000000 00000000 a01c7e80 ..............~.
0x807b0080 00000000 00000000 00000000 02000000 ................
0x807b0090 00000000 00000000 e46a7e80 40d37a80 .........j~.@.z.
The struct in reactos uses a ulonglong for the sector count and starting sector. one imagines that they wouldn't have disallowed disks greater than 4 gig on risc winnt, the thinkpad 860 was a machine that was $12000 at introduction in an era when we were installing 1 gig quantum fireballs with win95 like candy.