1. Hard Disks and I/O Polytechnic University CS2214 11/25/03

2. Input/Output

3. I/O contd. I/O bandwidth measurements How much data can be moved through system in a given time? E.g. supercomputer applications How many I/O operations can we do per unit of time? E.g. National Income Tax Service

4. I/O Characteristics Behavior Input (read once) Output (write only, cannot be read) Storage (can be reread and usually rewritten) Partner Human or machine or other end? Data Rate Peak rate at which data can be transferred between I/O device and main memory or processor.

5. I/O Characteristics Contd. DeviceBehaviorPartnerData Rate (KB/sec) KeyboardInputHuman.01 Line Printer OutputHuman1.00 ModemInput/ Output Machine2.00-8.00 Magnetic Disk StorageMachine2,000- 10,000

6. Common Hard Disk Parameters Data rate - Number of bytes per second that a drive can deliver to the CPU. Seek time - Amount of time between when the CPU requests a file and when the first byte of the file is sent to the CPU. Capacity - Number of bytes disk can hold

7. Inside A Hard Disk Sealed aluminum box with controller electronics attached to one side. Electronics control the read/write mechanism and the motor that spins the platters. Electronics are all contained on a small board that detaches from rest of the drive. www.howstuffworks.com

8. Inside A Hard Disk Contd. The platters spin at 3,600 or 7,200 rpm when the drive is operating. These platters are manufactured to amazing tolerances and are mirror- smooth. The arm that holds the read/write heads is controlled by the mechanism in the upper-left corner, and is able to move the heads from the hub to the edge of the drive. The arm and its movement mechanism are extremely light and fast. www.howstuffworks.com

9. Inside A Hard Disk Contd. www.howstuffworks.com

10. Hard Disk Access Times Seek time Rotational time Transfer time Controller time

11. Problem What is the average time to read or write 512 byte sector for a disk rotating at 5400 RPM? Average seek time is 12ms, transfer rate is 5MB/sec and controller overhead is 2ms. Average disk access time = T seek +T Rotational + T Transfer + T Controller =12ms + 5.6ms+.5KB/5MB/sec +2ms = 12+5.6+0.1+2 = 19.7 ms.

12. Hard Disk Animation Animation