Overview of Mass Storage Structure  Magnetic disks provide bulk of secondary storage of modern computers  Drives rotate at 60 to 200 times per second  Transfer rate is rate at which data flow between drive and computer  Positioning time (random-access time) is time to move disk arm to desired cylinder (seek time) and time for desired sector to rotate under the disk head (rotational latency)  Head crash results from disk head making contact with the disk surface  That’s bad  Disks can be removable  Drive attached to computer via I/O bus  Busses vary, including EIDE, ATA, SATA, USB, Fibre Channel, SCSI  Host controller in computer uses bus to talk to disk controller built into drive or storage array Operating System Concepts with Java – 8th Edition 12.4 Silberschatz, Galvin and Gagne ©2009
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Overview of Mass Storage Structure  Magnetic disks provide bulk of secondary storage of modern computers  Drives rotate at 60 to 250 times per second  Transfer rate is rate at which data flow between drive and computer  Positioning time (random-access time) is time to move disk arm to desired cylinder (seek time) and time for desired sector to rotate under the disk head (rotational latency)  Head crash results from disk head making contact with the disk surface  That’s bad  Disks can be removable  Drive attached to computer via I/O bus  Busses vary, including EIDE, ATA, SATA, USB, Fibre Channel, SCSI, SAS, Firewire  Host controller in computer uses bus to talk to disk controller built into drive or storage array Operating System Concepts Essentials – 8 th Edition 11.4 Silberschatz, Galvin and Gagne ©2011
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Overview of Mass Storage Structure  Magnetic disks provide bulk of secondary storage of modern computers  Drives rotate at 60 to 250 times per second  Transfer rate is rate at which data flow between drive and computer  Positioning time (random-access time) is time to move disk arm to desired cylinder (seek time) and time for desired sector to rotate under the disk head (rotational latency)  Head crash results from disk head making contact with the disk surface -- That’s bad  Disks can be removable  Drive attached to computer via I/O bus  Busses vary, including EIDE, ATA, SATA, USB, Fibre Channel, SCSI, SAS, Firewire  Host controller in computer uses bus to talk to disk controller built into drive or storage array Operating System Concepts Essentials – 2nd Edition 9.4 Silberschatz, Galvin and Gagne ©2013
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Ports and Connectors  What are USB ports? USB (universal serial bus) port can connect up to 127 different peripherals together with a single connector type PCs PCs typically typically have have six six to to eight USB USB ports on front front or or back back of of the the system system unit unit USB 2.0 p. 208 Single Single USB USB port port can can be be used used to attach multiple peripherals in in a daisy daisy chain chain First First USB USB device device connects connects to to USB USB port port on on computer computer Third Third USB USB device device connects connects to to second second USB USB device, device, and and so so on on Second Second USB USB device device connects connects to to first first USB USB device device Next
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Disk Scheduling  The operating system is responsible for using hardware efficiently — for the disk drives, this means having a fast access time and disk bandwidth  Access time has two major components  Seek time is the time for the disk to move the heads to the cylinder containing the desired sector  Rotational latency is the additional time waiting for the disk to rotate the desired sector to the disk head  Minimize seek time  Seek time  seek distance  Disk bandwidth is the total number of bytes transferred, divided by the total time between the first request for service and the completion of the last transfer Operating System Concepts with Java – 8th Edition 12.8 Silberschatz, Galvin and Gagne ©2009
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RAPTOR Syntax and Semantics - Arrays Array variable - Array variables are used to store many values (of the same type) without having to have many variable names. Instead of many variables names a count-controlled loop is used to gain access (index) the individual elements (values) of an array variable. RAPTOR has one and two dimensional arrays of numbers. A one dimensional array can be thought of as a sequence (or a list). A two dimensional array can be thought of as a table (grid or matrix). To create an array variable in RAPTOR, use it like an array variable. i.e. have an index, ex. Score[1], Values[x], Matrix[3,4], etc. All array variables are indexed starting with 1 and go up to the largest index used so far. RAPTOR array variables grow in size as needed. The assignment statement GPAs[24] ← 4.0 assigns the value 4.0 to the 24th element of the array GPAs. If the array variable GPAs had not been used before then the other 23 elements of the GPAs array are initialized to 0 at the same time. i.e. The array variable GPAs would have the following values: 1 2 3 4… Array variables in action- Arrays and count-controlled loop statements were made for each other. Notice in each example below the connection between the Loop Control Variable and the array index! Notice how the Length_Of function can be used in the count-controlled loop test! Notice that each example below is a count-controlled loop and has an Initialize, Test, Execute, and Modify part (I.T.E.M)! Assigning values to an array variable Reading values into an array variable Writing out an array variable’s values Computing the total and average of an array variable’s values Index ← 1 Index ← 1 Index ← 1 Total ← 0 Loop Loop Loop Index ← 1 PUT “The value of the array at position “ + Index + “ is “ + GPAs[Index] Loop GPAs[Index] ← 4.0 “Enter the GPA of student “” + Index + “: “ GET GPAs[Index] Index >= 24 Index >= 24 Index >= Length_Of (GPAs) Index ← Index + 1 Index ← Index + 1 Index ← Index + 1 Total ← Total + GPAs[Index] Index >= Length_Of(GPAs) Index ← Index + 1 … 23 24 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 4.0 The initialization of previous elements to 0 happens only when the array variable is created. Successive assignment statements to the GPAs variable affect only the individual element listed. For example, the following successive assignment statements GPAs[20] GPAs[11] ← ← 1.7 3.2 would place the value 1.7 into the 20th position of the array, and would place the value 3.2 into the 11th position of the array. i.e. GPAs[20] ← 1.7 GPAs[11] ← 3.2 1 2 3 4… … 23 24 Initialize the elements of a two dimensional array (A two dimensional array requires two loops) Row ← 1 Loop Average ← Total / Length_Of(GPAs) Find the largest value of all the values in an array variable Find the INDEX of the largest value of all the values in an array variable Highest_GPA ← GPAs[1] Highest_GPA_Index ←1 Index ← 1 Index ← 1 Loop Loop GPAs[Index] > Highest_GPA GPAs[Index] >= GPAs[Highest_GPA_Index] Column ← 1 Loop 0 0 0 0 0 0 0 0 0 0 3.2 0 0 0 0 0 0 0 0 1.7 0 0 0 4.0 An array variable name, like GPAs, refers to ALL elements of the array. Adding an index (position) to the array variable enables you to refer to any specific element of the array variable. Two dimensional arrays work similarly. i.e. Table[7,2] refers to the element in the 7 th row and 2nd column. Individual elements of an array can be used exactly like any other variable. E.g. the array element GPAs[5] can be used anywhere the number variable X can be used. The Length_Of function can be used to determine (and return) the number of elements that are associated with a particular array variable. For example, after all the above, Length_Of(GPAs) is 24. Matrix[Row, Column] ← 1 Column >= 20 Column ← Column + 1 Highest_GPA ← GPAs[Index] Highest_GPA_Index ← Index Index >= Length_Of(GPAs) Index >= Length_Of(GPAs) Index ← Index + 1 Index ← Index + 1 PUT “The highest GPA is “ + Highest_GPA¶ PUT “The highest GPA is “ + GPAs[Highest_GPA_Index] + “ it is at position “ + Highest_GPA_Index¶ Row >= 20 Row ← Row + 1
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