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University of Tehran 1 Interface Design Secondary Storage Omid Fatemi.

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Presentation on theme: "University of Tehran 1 Interface Design Secondary Storage Omid Fatemi."— Presentation transcript:

1 University of Tehran 1 Interface Design Secondary Storage Omid Fatemi

2 University of Tehran 2 Outline

3 University of Tehran 3 PC disk drives 1 st were diskette Then hard drives Then removable drives

4 University of Tehran 4 Diskette Drives for a PC Magnetic One or more circular disks that are coated with material that responds to magnetic fields Disks are mounted on spindle and turn under head(s) that move radially in and out to read/write data

5 University of Tehran 5 Disk Organization

6 University of Tehran 6 Formats Original drives 5 ¼, today 3 ½ K to 1.44/2 M Microsoft Distribution Format (2 M) IBM – eXtended Diskette Format (2M) XDF Even have 2.88 diskette (but requires special drive)

7 University of Tehran 7 Disk Size

8 University of Tehran 8 Hard Disks Disks are harder material – platters Platter – rigid disks made of aluminum or glass Data is encoded before storage to ensure that the patterns of 0s and 1s changes enough for heads to read/write them correctly

9 University of Tehran 9 Access Time In the range of 10ms Seek time Settling time Latency time –relates to rotation speed (RPM) Controller overhead

10 University of Tehran 10 Encoding Formats MFM – Modified Frequency Modulation encoding RLL – Run Length Limited encoding ESDI (enhanced small device interface) SCSI (small computer system interface) IDE (integrated device electronics) E-IDE

11 University of Tehran 11 Encoding

12 University of Tehran 12 Run Length Limit Data: Code:

13 University of Tehran 13 ESDI, IDE Like MFM and RLL, but allows for larger capacity drives and speed Died quickly when IDE (integrated device electronics) drives appeared. EIDE is extension of IDE Controller electronics are on circuit card on the side of the drive and not on a plug in I/O card. AT attachment packet interface (ATAPI) –Extended EIDE –Accommodates other devices besides hard drives – CD ROMs for example.

14 University of Tehran 14 Hard Disks

15 University of Tehran 15 Hard Disk Interleaving

16 University of Tehran 16 SCSI Tiny one-computer local area network Requires SCSI host adapter Multiple SCSI devices can be connected together (drives and other peripheral devised)

17 University of Tehran 17 DOS Disk Overview Fundamental unit of storage is sector –Usually 512 bytes of information Each sector is actually 571 bytes –remaining is header and trailer for each footer –checksum data for verification of data accuracy All sectors around a disk at a given distance form a track. With multiple disks, tracks form cylinders Most disk can be recorded on both sides

18 University of Tehran 18 Physical Versus Logical Formatting of Disks Physical – set up the sectors/tracks that will be used Logical– add in the operating system component (such as DOS header/trailer information) –Boot record (if disk is bootable) –FAT – File Allocation Table –Root directory

19 University of Tehran 19 Bad Sectors Diskette –Sectors are marked and capacity id reduced by number of bad sectors Hard Disk –Spare sectors are held in reserve and used to replace the bad ones »Defragmentation of drive will optimize performance

20 University of Tehran 20 Integrity Maintenance Cyclical Redundancy Check (CRC) Diskettes try and then report Abort, Retry, or Fail Hard Drives also have ECC, so if can, errors are fixed

21 University of Tehran 21 Logical Structure FAT 12 or FAT16 –DOS boot sector –FAT #1 –FAT #2 –Root Directory –Data area

22 University of Tehran 22 FAT 32 –DOS boot record (3 sectors) –Reserved sectors –Copy of boot –Reserved sectors –FAT #1 –FAT #2 –Data area

23 University of Tehran 23 Clusters Minimum amount of space that can be allocated to a file Means that if cluster is 4K, and file is 1K, then to store file use 4K Unused portion is called slack space

24 University of Tehran 24 FAT usage FAT 12 –Floppy diskettes, hard disks of less than 16M – (0 to 4086 values) –For hard disks, the cluster size is 4K

25 University of Tehran 25 FAT 16 –16 bit numbers –Up to 2 GB drive –Cluster size of 2K for drives less than 128M –Cluster size doubles every time capacity doubles, so 2G means cluster size of 32K

26 University of Tehran 26 FAT 32 –32 bits (4 bytes) –Minimum 512K, up to 2048G –(32 bit number, but 28 are cluster, 4 are reserved – so only 268,435,456 clusters max) –FAT can be up to 1G

27 University of Tehran 27 Root directory Part of FAT 12 and 16 Not part of FAT 32 Is the directory board Subdirectories are pointed to by their parents, themselves and their children

28 University of Tehran 28 FAT table Huge table of numbers Starts at address 2 Each number is twelve bits 0 means it is unused EOF means that it is end of file 3 rd for bad sector Any other number means address of next cluster as part of file

29 University of Tehran 29 Floppy Layout

30 University of Tehran 30 Boot Record Layout L CS: D CS:100 17F

31 University of Tehran 31 Directory Layout L CS: D CS:200 27F

32 University of Tehran 32 FAT Layout L CS: D CS:100 L100

33 University of Tehran 33 Logical Differences between diskettes and hard disks MBR – Master Boot Record Hard drives have an MBR that not only contains boot information, but also table of the drive partitioning

34 University of Tehran 34 Drive Partitioning Primary logical volume. Hidden partition. Extended partition. Each disk can have only 1 active primary partition – all others are hidden. Each disk can also only have 1 extended partition. A logical volume is all the storage space referred to by a single drive letter. An extended partition can have any number of logical volumes.

35 University of Tehran 35 LBA vs. CSH Partitioning involves separating blocks of storage in terms of cylinder, head and section numbers. Table may actually use logical block address (LBA) numbering, so the division numbers shown in the table listing (as seen in your disk editor) may have no relationship with an actual cylinder start on the physical drive.

36 University of Tehran 36 Partitions Hidden partitions can house other operating systems When booting, you choose between the operating systems When booted DOS can only see one active partition and generally does not see the other hidden partitions; however, some OS s like Unix and Linux can see their partition as well as the DOS partitions

37 University of Tehran 37 Managing Multiple Disk Drives Floppy diskettes –Connect via 34-wire ribbon cables typically. These cables can have 0, 1, or 2 drives. –Drive connected to middle connection is B:, one at end will be A:

38 University of Tehran 38 IDE Hard Disks IDE –Connect via special connectors or option cards –Current versions of the IDE allow four IDE channel, each channel supporting 2 devices –Most PCs support two EIDE –Jumpers determine if drive is master or slave, the first drive is usually the master, and the rest are slaves –Hard drive wires are wider and not twisted with 3 connectors typically –On each IDE channel, you have one master and then 1 slave

39 University of Tehran 39 IDE vs. EIDE

40 University of Tehran 40 IDE Connections

41 University of Tehran 41 IDE Registers

42 University of Tehran 42 SCSI –All their controller electronics are on the device –Operate over a SCSI bus with SCSI host adapter –Some PCs (like Macintosh computers) have SCSI host adapter built in –Host adapter typically plugs into a PCI bus »Adaptec 2940W/UW »Has 2 internal connectors (one for narrow, one for ultra wide) »External connector (ultra wide)

43 University of Tehran 43 SMART Drives Self-Monitoring and Reporting Technology Set flags that the BIOS can read and then report

44 University of Tehran 44 RAID Redundant arrays of inexpensive disks Data is stored on more than one disk and then you can avoid or minimize downtime 9 levels In some cases, allows hot swaps of drives or power supplies when they have failed Formerly used only on mainframe computers and large servers

45 University of Tehran 45 Tape Drives Earliest type converted digital to audio and stored it on audio cassettes Digital Audio Tape – special purpose drives meant just for digital data recording Capacities go up to 24G Downside – sequential access only, and sometimes not reliable in terms of functionality Advantage – great for drive backups

46 University of Tehran 46 Removable disks Uses a docking bay Plug in drive, put data into it, then remove it Can hot swap Alternative is external drive (through parallel port)

47 University of Tehran 47 Hard disks with removable platters Store data, then swap platters Downside: even 1 particle of dust can cause damage Typically best if external drive

48 University of Tehran 48 Super Floppy Diskette drives Uses advanced head positioning mechanism as hard drives Also heads can not touch disk as much as normal floppy heads do – to reduce wear

49 University of Tehran 49 Zip Drives Larger than 3 ½ 100M and 250 M Internal and external modes ZIP drives appear as additional logic drives Over parallel port, performance is slow Over SCSI, approaches performance of a hard drive

50 University of Tehran 50 Optical PC CD ROM, CD-R, CD-RW Only one side of CD is typically used Binary data stored and read optically Bits are stored more densely Pits burned to alter reflection of laser light –Encode the data –Signal where spiral track goes

51 University of Tehran 51 Optical Data

52 University of Tehran 52 CD ROM drives Differ in in standard, but can share some parts and design Red, Orange, Yellow, Green, White, and Blue Book Storage capacity of around 650M or better Can only be read, not written

53 University of Tehran 53 CD – R Disk are gold or silver and deep green or cyan on recordable side Silver/cyan is Type II (to reflect red lasers used in DVD Can be read in ROM drives, but written in CD- R Laser operates at three or more power levels – at highest, it burns pits Write once read many (worm)

54 University of Tehran 54 CD-RW Has two more layers on disk than CD-R Recordable layer is made of alloy of several metals Melts regions to switch from crystalline form to data form Enough temperature, and they go back to crystalline form, allowing for a rewrite Marks are not as good at light-scattering, so not all CD drives can read them

55 University of Tehran 55 Digital Versatile Disc DVD Higher capacity Tuned to red band of visible light spectrum Data is more densely packed Can be double sided – 17G or more MPEG2 standard Requires special decoders and copy- protection circuitry

56 University of Tehran 56 DVD Drive Can read CD-ROMs but not as fast as best CD-ROM drives DVD ram is still under discussion, but there is one standard in place Allows for 2.6G or more per side as storage DVD RAM discs are in sealed cartridges and can only be used in DVD RAM drives

57 University of Tehran 57 Magneto-Optical Expensive Large platter formats Material is magnetized at all times Coercivity – how easily you can switch magnetization from one orientation to another MO s have coercivity over 10 times higher than floppies Because of this, cant store to small spaces easily (for more dense packing)

58 University of Tehran 58 Laser is used to take material to CURIE temperature (where low magnetic field can be used), and so denser packing can be done When it cools, it returns to higher state Read by using a laser beam used to read polarity (polarizer)

59 University of Tehran 59 Data Compression Compressing data so that storage is increased without changing the disks Two forms –Compressing individual files through utility (such as WINZIP) –OS compression – all data automatically compressed by the OS Downside: data has to be compressed then uncompressed to be read Useful for archiving data

60 University of Tehran 60 OS Data Compression DoubleSpace, DriveSpace for example Requires extra driver OS takes care of compression While tested, errors can occur; so keep backups

61 University of Tehran 61 Problems 1, 22, 24 25, 29 31, 33, 34


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