Input/Output
Processor
Cache
Memory I/O bus
Main Memory I/O controller I/O controller I/O controller
Graphics output Network
Interrupts
Disk
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
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.
I/O Characteristics Contd.
Device Behavior Partner Data Rate (KB/sec)
Keyboard Input Human .01
Line Printer
Output Human 1.00
Modem Input/ Output
Machine 2.00-8.00
Magnetic Disk
Storage Machine 2,000-10,000
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
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
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
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
= Tseek+TRotational+ TTransfer+ TController
=12ms + 5.6ms+.5KB/5MB/sec +2ms
= 12+5.6+0.1+2
= 19.7 ms.