Unformatted text preview: Midterm Exam Friday, May 8 Project #2 Scores are posted Median = 86% Scores are posted Project Reviews: Project #3 evaluation criteria are posted Most are really very good Some show additional insight Some tell me practically nothing Review credit does not depend on how much you contributed Project #4 will be posted today Plans of Attack (Nice !) Questions? Today's topics I/O Unit Block/Character Devices Magnetic Disks Input / Output unit I/O unit Interface with peripherals Initiates input / output tasks Manages buffers Handles error signals Hardware/Software boundary of "I/O unit" is not universally defined I/O Hardware Variety of I/O devices Common concepts Keyboard, mouse, game device, monitor, printer, scanner, etc. Many specialized devices Port (internal/external, physical/logical) Bus (shared direct access / daisy chain ) Controller (host adapter) Driver (software interface OS controller) Ports A physical port is an interface to which a device can be connected Internal (usually parallel bus) External (usually serial bus) modem, printer, mouse, etc. disk drive, display screen, keyboard Ports A logical port is a structure used by system commands can specify either memorymapped I/O or portmapped I/O hides differences among physical ports System commands use the same instructions to communicate with main memory and I/O devices. I/O instructions I/O instructions control devices When a process issues an I/O request ... Process may be sent to a device queue CPU Interrupt request line is triggered by an I/O request or by an I/O device I/O may be "blocking" (process must wait) or "non blocking" (process may proceed) Interrupt vector is checked to dispatch interrupt to correct handler Application I/O Interface I/O system calls encapsulate device behaviours in generic classes Devicedriver layer hides differences among I/O controllers from the kernel Device drivers have addresses, used by system I/O commands I/O device drivers are addressed at reserved address ranges in main memory A Kernel I/O Structure Characteristics of I/O Devices Actual devices vary in many aspects Data transfer mode Access method Transfer timing Sharing Device speed I/O direction Character devices Character and Block Devices
keyboard, mouse, serial port, etc. sequential access stream of bytes disk drives, etc. nonsequential (random) access Different enough from block and character to have special interface Block devices Network devices Magnetic Disks Most secondary storage is provided by magnetic disks Magnetic disks are block devices Disk I/O is one of the slowest operations in the entire system. Magnetic Disk Fundamentals Tracks and Sectors Magnetic Disk Fundamentals Position on disk (physical address) is uniquely specified by <cylinder,track,sector> triplet Disk drive is addressed as an array of logical blocks Each block number (logical address) is mapped to a unique <cylinder,track,sector> triplet. logical block is the smallest unit that can be transferred, i.e. a sector LBA mode Mapping is usually done at the hardware level Block 0 is <0,0,0>. Mapping proceeds sequentially through a track, then the rest of the tracks in a cylinder, and then through the rest of the cylinders from outermost to innermost. Questions? Project #3 Read Love Chapter 13 Start reading Project #4 Due Sunday before midnight CDA is due Monday (end of class) Review document is due Monday before midnight ...
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- Spring '08
- Operating Systems, Input/output, disk I/O