1. Slide 5-1 Copyright © 2004 Pearson Education, Inc. Operating Systems: A Modern Perspective, Chapter 5

2. Slide 5-2 Copyright © 2004 Pearson Education, Inc. Operating Systems: A Modern Perspective, Chapter 5 5 Device Management

3. Slide 5-3 Copyright © 2004 Pearson Education, Inc. Operating Systems: A Modern Perspective, Chapter 5 Input/Output Devices Input Device Processor Output Device

4. Slide 5-4 Copyright © 2004 Pearson Education, Inc. Operating Systems: A Modern Perspective, Chapter 5 The Device Driver Interface Device Interface … write(…); … Terminal Driver Terminal Driver Printer Driver Printer Driver Disk Driver Disk Driver Terminal Controller Terminal Controller Printer Controller Printer Controller Disk Controller Disk Controller

5. Slide 5-5 Copyright © 2004 Pearson Education, Inc. Operating Systems: A Modern Perspective, Chapter 5 Device Management Organization Application Process Application Process File Manager File Manager Device Controller Command Status Data Hardware Interface System Interface Device-Independent Device-Dependent

6. Slide 5-6 Copyright © 2004 Pearson Education, Inc. Operating Systems: A Modern Perspective, Chapter 5 System Call Interface Functions available to application programs Abstract all devices (and files) to a few interfaces Make interfaces as similar as possible –Block vs character –Sequential vs direct access Device driver implements functions (one entry point per API function)

7. Slide 5-7 Copyright © 2004 Pearson Education, Inc. Operating Systems: A Modern Perspective, Chapter 5 Example: BSD UNIX Driver open Prepare dev for operation close No longer using the device ioctl Character dev specific info read Character dev input op write Character dev output op strategy Block dev input/output ops select Character dev check for data stop Discontinue a stream output op

8. Slide 5-8 Copyright © 2004 Pearson Education, Inc. Operating Systems: A Modern Perspective, Chapter 5 Overlapping the Operation of a Device and the CPU Variable x Register Data on device... read(dev_I, “%d”, x); y = f(x)... Device dev_I Memory CPU... startRead(dev_I, “%d”, x);... While(stillReading()) ; y = f(x)...

9. Slide 5-9 Copyright © 2004 Pearson Education, Inc. Operating Systems: A Modern Perspective, Chapter 5 Overlapping CPU-Controller Operations in a Process App I/O Ctlr t1t1 t2t2 t3t3 t4t4 t5t5 t6t6 t7t7 t8t8 t9t9

10. Slide 5-10 Copyright © 2004 Pearson Education, Inc. Operating Systems: A Modern Perspective, Chapter 5 Overlapping Processing and I/O App 1 App 2 I/O Ctlr t1t1 t2t2 t3t3 t4t4

11. Slide 5-11 Copyright © 2004 Pearson Education, Inc. Operating Systems: A Modern Perspective, Chapter 5 Driver-Kernel Interface Drivers are distinct from main part of kernel Kernel makes calls on specific functions, drivers implement them Drivers use kernel functions for: –Device allocation –Resource (e.g., memory) allocation –Scheduling –etc. (varies from OS to OS)

12. Slide 5-12 Copyright © 2004 Pearson Education, Inc. Operating Systems: A Modern Perspective, Chapter 5 The Pure Cycle Water Company Water CompanyCustomer Office Water Consumers Water Producer Delivering Water Returning the Empties

13. Slide 5-13 Copyright © 2004 Pearson Education, Inc. Operating Systems: A Modern Perspective, Chapter 5 Hardware Buffering Process Controller Data Device Process Controller B Device A Process Controller B Device A Unbuffered Process reads b i-1 Controller reads b i Process reads b i Controller reads b i+1

14. Slide 5-14 Copyright © 2004 Pearson Education, Inc. Operating Systems: A Modern Perspective, Chapter 5 Double Buffering in the Driver Process Controller B Device A Process Controller B Device A BABA Hardware Driver

15. Slide 5-15 Copyright © 2004 Pearson Education, Inc. Operating Systems: A Modern Perspective, Chapter 5 Circular Buffering From data producer To data consumer Buffer i Buffer j

16. Slide 5-16 Copyright © 2004 Pearson Education, Inc. Operating Systems: A Modern Perspective, Chapter 5 Rotating Media Track (Cylinder) Sector (a) Multi-surface Disk(b) Disk Surface(b) Cylinders Cylinder (set of tracks)

17. Slide 5-17 Copyright © 2004 Pearson Education, Inc. Operating Systems: A Modern Perspective, Chapter 5 Storage Device Magnetic Disk (SCSI) Controller Driver Get disk description Set SCSI parms read/write ops Interrupt hander SCSI API commands bits per byte etc. Device Driver API

18. Slide 5-18 Copyright © 2004 Pearson Education, Inc. Operating Systems: A Modern Perspective, Chapter 5 Compute vs I/O Bound Compute-bound I/O-bound Time

19. Slide 5-19 Copyright © 2004 Pearson Education, Inc. Operating Systems: A Modern Perspective, Chapter 5 Disk Optimizations Transfer Time: Time to copy bits from disk surface to memory Disk latency time: Rotational delay waiting for proper sector to rotate under R/W head Disk seek time: Delay while R/W head moves to the destination track/cylinder Access Time = seek + latency + transfer

20. Slide 5-20 Copyright © 2004 Pearson Education, Inc. Operating Systems: A Modern Perspective, Chapter 5 Optimizing Seek Time Multiprogramming on I/O-bound programs => set of processes waiting for disk Seek time dominates access time => minimize seek time across the set Tracks 0:99; Head at track 75, requests for 23, 87, 36, 93, 66 FCFS: 52+ 64 + 51 + 57 + 27 = 251 steps

21. Slide 5-21 Copyright © 2004 Pearson Education, Inc. Operating Systems: A Modern Perspective, Chapter 5 Optimizing Seek Time (cont) Requests = 23, 87, 36, 93, 66 SSTF: (75), 66, 87, 93, 36, 23 –9 + 21 + 6 + 57 + 13 = 106 steps Scan: (75), 87, 93, 99, 66, 36, 23 –12 + 6 + 6 + 33 + 30 + 13 = 100 steps Look: (75), 87, 93, 66, 36, 23 –12 + 6 + 27 + 30 + 13 = 87 steps

22. Slide 5-22 Copyright © 2004 Pearson Education, Inc. Operating Systems: A Modern Perspective, Chapter 5 Optimizing Seek Time (cont) Requests = 23, 87, 36, 93, 66 Circular Scan: (75), 87, 93, 99, 23, 36, 66 –12 + 6 + 6 + home + 23 + 13 + 30 = 90 + home Circular Look: (75), 87, 93, 23, 36, 66 –12 + 6 + home + 23 + 13 + 30 = 84 + home