Device Management

52 Pages·2013·1.6 MB·English

Operating Systems
Lecture #4: IO Management
WrittenbyDavidGoodwin
basedonthelectureseriesofDr. DayouLi
andthebookUnderstandingOperatingSystems4thed.
byI.M.FlynnandA.McIverMcHoes (2006)
DepartmentofComputerScienceandTechnology,
UniversityofBedfordshire.
OperatingSystems,2013
18th February 2013
Outline
Lecture#4IO
Management 1 Device types
DavidGoodwin
Universityof 2 DASD
Bedfordshire
3 Components of IO subsystem
Devicetypes
DASD 4 Communication
ComponentsofIO Polling & Interrupts
subsystem
Communication DMA
Polling&Interrupts Buffers
DMA
Buffers 5 Management of IO requests
ManagementofIO
requests 6 Device Handling Algorithms
DeviceHandling FCFS
Algorithms
FCFS SSTF
SSTF SCAN
SCAN
RAID 7 RAID
summary
8 summary
OperatingSystems 52
Lecture#4IO
Management
DavidGoodwin
Universityof
Bedfordshire
Devicetypes 3
Device types
DASD
ComponentsofIO
subsystem
Communication
Polling&Interrupts
DMA
Buffers
ManagementofIO
requests
DeviceHandling
Algorithms
FCFS
SSTF
SCAN
RAID
summary
OperatingSystems 52
I/O HARDWARE
Lecture#4IO
Management
DavidGoodwin
Universityof
Bedfordshire
Devicetypes 4 (cid:136) Incredible variety of I/O devices
DASD (cid:136) Common concepts
ComponentsofIO
subsystem (cid:136) Port
Communication (cid:136) Bus (daisy chain or shared direct access)
Polling&Interrupts (cid:136) Controller (host adapter)
DMA
Buffers (cid:136) I/O instructions control devices
ManagementofIO (cid:136) Devices have addresses, used by
requests
DeviceHandling (cid:136) Memory-mapped I/O
Algorithms (cid:136) Direct I/O instructions
FCFS
SSTF
SCAN
RAID
summary
OperatingSystems 52
TYPES OF DEVICES
Lecture#4IO
Management
DavidGoodwin
Universityof
Bedfordshire (cid:136) Dedicated
Devicetypes 5 (cid:136) Assigned to only one job at a time, e.g. printers, tape drives,
DASD etc.
ComponentsofIO (cid:136) Shared
subsystem
Communication (cid:136) Can be assigned to several processes, e.g. a disk can be
Polling&Interrupts shared by several processes at the same time by interleaving
DMA
their requests which are carefully controlled by the Device
Buffers
Manager.
ManagementofIO
requests (cid:136) Virtual
DeviceHandling
Algorithms (cid:136) A combination of the first two –dedicated devices transferred
FCFS to shared devices, e.g. a printer made sharable through
SSTF
spooling (Simultaneous Peripheral Operation On-Line).
SCAN
RAID
summary
OperatingSystems 52
STORAGE DEVICES
Lecture#4IO
Management
DavidGoodwin (cid:136) Sequential access storage
Universityof
Bedfordshire (cid:136) Paper printout, punch cards, paper tapes, magnetic tapes
Devicetypes 6 (cid:136) Direct access storage devices (DASDs)
DASD (cid:136) Magnetic disks (fixed-head and moveable-head)
ComponentsofIO (cid:136) Optical discs (CD-ROM, CD-Recordable, CD-Rewritable,
subsystem
DVD)
Communication
Polling&Interrupts (cid:136) Magneto-optical (combination of magnetic and optical discs)
DMA (cid:136) Flash memory
Buffers
(cid:136) Removable medium that emulates random access memory
ManagementofIO
requests but unlike RAM, it stores data securely even it is removed
DeviceHandling from its power supply
Algorithms
FCFS (cid:136) RAID (Redundant Array of Inexpensive/independent Disks)
SSTF
(cid:136) A set of physical disk drives viewed as a single logical unit by
SCAN
RAID OS to close the widening gap between increasingly fast
summary processors and slower disk drives
OperatingSystems 52
Lecture#4IO
Management
DavidGoodwin
Universityof
Bedfordshire
Devicetypes
DASD
DASD 7
ComponentsofIO
subsystem
Communication
Polling&Interrupts
DMA
Buffers
ManagementofIO
requests
DeviceHandling
Algorithms
FCFS
SSTF
SCAN
RAID
summary
OperatingSystems 52
DASD ACCESS TIMES
Lecture#4IO
Management
DavidGoodwin
Universityof
Bedfordshire
Devicetypes (cid:136) For a fixed-head DASD
DASD 8
Total access time(t )=
a
ComponentsofIO
subsystem Sum of search time(ts)+Transfer time(tt)
Communication (cid:136) Search time t
s
Polling&Interrupts Best search time t =0
DMA s
Worst search time t =r (r is time taken per revolution of
Buffers s
disk)
ManagementofIO
requests r
Average search time t =
DeviceHandling s 2
Algorithms (cid:136) Transfer time t
t
FCFS
SSTF
SCAN
RAID
summary
OperatingSystems 52
DASD ACCESS TIMES
Lecture#4IO
Management
DavidGoodwin
Universityof
Bedfordshire (cid:136) Example for a fixed-head DASD
Devicetypes
DASD 9 A complete revolution takes 14ms, and data transfer time is
ComponentsofIO 0.16ms per record. Calculate
subsystem
Communication (cid:136) Total average access time for 20 individual records
Polling&Interrupts (cid:136) Total average access time for a block of 20 records
DMA (cid:136) Time saving between the two
Buffers
ManagementofIO (cid:18)14 (cid:19)
requests (cid:136) t for 20 individual records =20 +0.16 =143.2ms
a 2
DeviceHandling
Algorithms 14
(cid:136) t for block of 20 records = +20×0.16=10.2ms
FCFS a 2
SSTF (cid:136) Time saving =143.2–10.2=133.0ms
SCAN
RAID
summary
OperatingSystems 52
Lecture#4IO
Management
DavidGoodwin
Universityof
Bedfordshire
Components of IO
Devicetypes
DASD
ComponentsofIO 10 subsystem
subsystem
Communication
Polling&Interrupts
DMA
Buffers
ManagementofIO
requests
DeviceHandling
Algorithms
FCFS
SSTF
SCAN
RAID
summary
OperatingSystems 52