To format a floppy disk to the default SAM Coupé 10-sector format:
SAMdisk format a:
To format a floppy disk to the 18-sector format used by 1.44M DOS disks:
SAMdisk format a: -s18
Note: that this lays the soft-sector format, but doesn't write any logical DOS structures to the disk. In most cases it's better to write a disk image of a pre-formatted disk to achieve this.
To format a floppy disk to the 9-sector format used by 720K DOS disks:
SAMdisk format a: -s9
The track size is too big for double-density, so high density is selected automatically.
To unformat the first 4 cylinders on head 0:
SAMdisk unformat a: -c4 -h0
This writes empty tracks containing no sectors. It's not suitable for erasing single-density media to re-use in a modern drive (with narrower head). For that you'll need to use a demagnetiser.
To format a hard disk or compact flash card the default Atom Lite BDOS format:
SAMdisk format 1:
To format a drive to the legacy Atom BDOS format:
SAMdisk format 1: --atom
To wipe a drive, with simple zero-filling:
SAMdisk format 1: --no-sig