The movement of the hard drive's read/write heads over different areas of the disk when accessing fragmented files is slower, compared to accessing the entire contents of a non-fragmented file sequentially without moving the read/write heads to seek other fragments.
The dorsal fins are small and at the base of the tail. The largest mantas can reach 1,350 kg (2,980 lb). In both species the width is approximately 2.2 times the length of the body; M. birostris reaches at least 7 m (23 ft) in width while M. alfredi reaches about 5.5 m (18 ft).
Both the largest species of this order and the largest of all rays is the manta ray (Manta birostris). This peaceful leviathan can reach a size of 3,000 kg (6,600 lb), a disk width of 9.1 m (30 ft) and a total length of 5 m (16 ft). A related species reaches barely smaller sizes, the devil fish (Mobula mobular).