lecture10 - CSCC69H Lecture 10 Dan Zingaro July 12, 2010...

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Unformatted text preview: CSCC69H Lecture 10 Dan Zingaro July 12, 2010 File Concept I A file is a named collection of data with some properties I Contents, size, owner, last read/write time, protection, etc. I A file can also have a type I The type can be Understood by the file system (implementation type) I e.g. Directory, block special file, character special file, link I Type can be understood by other parts of the OS or the user (logical type) I e.g. Executable, dll, source code, object code, text File Concept... I A files type can be encoded in its name or contents I Windows encodes type in name I e.g. .com, .exe, .bat, .dll, .jpg , etc. I Unix encodes type in contents (sometimes) I e.g. Magic numbers, initial characters ( #! for shell scripts) Disk Storage Technology I A disk drive stores fixed-sized blocks of data known as sectors I Interface between disk drive and computer is like an array of sectors I Computer can ask disk controller to perform two basic operations I Write data from a specified physical address in memory to a specified sector number I Read data from a specified sector to a specified physical address in memory Disk Storage Technology... From Hailperin, Figure 8.1. Platter Spindle Head Head arm Pivot for head arm Disk Storage Technology... I Disk drive contains a stack of platters mounted on a common spindle, spinning at a fixed rotational speed I Each surface has a recording and a playback head I Heads are supported by an arm that can pivot the head closer or further from the spindle I Track: circular region of a single disk surface; readable by a head in a fixed position as the disk rotates I Cylinder: collection of tracks, one per surface, accessible at a particular position of the head arm I Head switch: changing the active head to provide access to another track in the same cylinder Disk Storage Technology... I Seek: moving arm closer to or further from the spindle, providing access to other cylinders I Seek time is larger for tracks that are further apart, but not proportionally I Disk arm must accelerate, decelerate, and settle I Seeking thousands of tracks away may take only ten times as long as seeking to an adjoining track I Rotational latency: waiting for the appropriate sector to come around to the heads position I It is comparable to the time necessary to seek across tens of thousands of tracks I So, total access time for a random sector on an adjoining track is brought to within a small factor of access time for a sector on a distant track I However, once an access is under way, additional sectors can be read or written at high speed as they pass under the head Exercise: Read Time I Bytes per track: 131072 I Rotational latency: 8 . 33 msec I Average seek time: 10 msec I How long does it take to read a block of 1 byte?...
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This note was uploaded on 02/05/2011 for the course CS 69 taught by Professor Cathy during the Summer '10 term at University of Toronto- Toronto.

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lecture10 - CSCC69H Lecture 10 Dan Zingaro July 12, 2010...

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