Disk Access Characteristics
•Disk latency = time between when command is issued and when data is in memory
•Is not following Moore’s Law!
•
•Disk latency = seek time + rotational latency
–Seek time = time for the head to reach cylinder
•10ms – 40ms
–Rotational latency = time for the sector to rotate
•Rotation time = 10ms
•Average latency = 10ms/2
•Transfer time = typically 10MB/s
•Disks read/write one block at a time (typically 4kB)