HelenOS sources

BOOT_BLOCK_IDX    419 uspace/app/sysinst/sysinst.c 	rc = block_read_direct(sid, BOOT_BLOCK_IDX, 1, bbuf);
BOOT_BLOCK_IDX    448 uspace/app/sysinst/sysinst.c 	rc = block_write_direct(sid, BOOT_BLOCK_IDX, 1, bbuf);
HelenOS homepage, sources at GitHub