Columbia COMS W4118 - Device Drivers (18 pages)

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Device Drivers



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Device Drivers

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Lecture Notes


Pages:
18
School:
Columbia University
Course:
Coms W4118 - Operating Systems I

Unformatted text preview:

Device Drivers 1 36 I O and Operating Systems As previously discussed all I O must go through the operating system A typical system has or could have many different types of devices What kind of software talks to these devices What is the interface between the OS and that software What is the interface to application programs Are there any hardware constraints 1 36 I O Models All operating systems impose tight controls on disk access because the OS itself needs to access the disk and control file storage Operating systems frequently provide high level access to common types of devices serial ports printers tapes etc Some operating systems permit user specified complex I O to some devices tapes displays The more normal an I O device is the more likely it is to be accessed by a standard model Try for an I O model that lets most applications be device independent 2 36 1 The Unix Model Two categories block devices and character devices File systems live on top of block devices Block devices are designed for give me N blocks starting at block number M Almost never used directly by the application programmer Character devices everything else return a series of unstructured bytes Provides a high degree of device independence for most applications 3 36 The Windows Model More oriented towards bit maps Screens are bitmaps Printers are bitmaps Disks Disks use the same block model as in Unix 4 36 2 Networking Network devices are completely different They re neither block nor character oriented They re used very differently by the OS 5 36 I O Model Character devices Block devices Bitmaps Networks 6 36 3 Unix I O 7 36 Back to Unix All devices have filenames ls time style Ggl dev sda1 dev pts 6 crw w 1 136 6 dev pts 6 brw rw 1 8 1 dev sda1 The c indicates a character I O devices the b indicates a block device The 136 and the 8 are major device numbers The 6 and the 1 are minor device numbers Device files are created with mknod 7 36 Major Device Numbers Major device numbers



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