diskgeometry tag

#define HWI_TAG_NAME_diskgeometry   "diskgeometry"
#define HWI_TAG_ALIGN_diskgeometry  (sizeof(uint32))
struct hwi_diskgeometry {
    struct hwi_prefix   prefix;
    uint8_t             disknumber;
    uint8_t             sectorsize;   /* as a power of two */
    uint16_t            heads;
    uint16_t            cyls;
    uint16_t            sectors;
    uint32_t            nblocks;

Note that this is a simple tag, not an item. This is an x86-only mechanism used to transfer the information from the BIOS about disk geometry.