The device syntax is like this:
‘’ means the parameter is optional. device depends on the disk driver in use. BIOS and EFI disks use either ‘fd’ or ‘hd’ followed by a digit, like ‘fd0’, or ‘cd’. AHCI, PATA (ata), crypto, USB use the name of driver followed by a number. Memdisk and host are limited to one disk and so it's refered just by driver name. RAID (md), ofdisk (ieee1275 and nand), LVM (lv), LDM and arcdisk (arc) use intrinsic name of disk prefixed by driver name. Additionally just “nand” refers to the disk aliased as “nand”. Conflicts are solved by suffixing a number if necessarry. Commas need to be escaped. Loopback uses whatever name specified to loopback command. Hostdisk uses names specified in device.map as long as it's of the form [fhc]d[0-9]* or hostdisk/<OS DEVICE>. For crypto and RAID (md) additionally you can use the syntax <driver name>uuid/<uuid>.
(fd0) (hd0) (cd) (ahci0) (ata0) (crypto0) (usb0) (cryptouuid/123456789abcdef0123456789abcdef0) (mduuid/123456789abcdef0123456789abcdef0) (lv/system-root) (md/myraid) (md/0) (ieee1275/disk2) (ieee1275//pci@1f\,0/ide@d/disk@2) (nand) (memdisk) (host) (myloop) (hostdisk//dev/sda)
part-num represents the partition number of device, starting from one. partname is optional but is recommended since disk may have several top-level partmaps. Specifying third and later component you can access to subpartitions.
The syntax ‘(hd0)’ represents using the entire disk (or the MBR when installing GRUB), while the syntax ‘(hd0,1)’ represents using the first partition of the disk (or the boot sector of the partition when installing GRUB).
(hd0,msdos1) (hd0,msdos1,msdos5) (hd0,msdos1,bsd3) (hd0,netbsd1) (hd0,gpt1) (hd0,1,3)
If you enabled the network support, the special drives ‘(tftp)’, ‘(http)’ and so on ars also available. Before using the network drive, you must initialize the network. See Network, for more information.
If you boot GRUB from a CD-ROM, ‘(cd)’ is available. See Making a GRUB bootable CD-ROM, for details.