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Section 6.2. Record data by magnetizing the binary code on the surface of a disk. Data area is reusable Allows for both sequential and direct access file.

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Presentation on theme: "Section 6.2. Record data by magnetizing the binary code on the surface of a disk. Data area is reusable Allows for both sequential and direct access file."— Presentation transcript:

1 Section 6.2

2 Record data by magnetizing the binary code on the surface of a disk. Data area is reusable Allows for both sequential and direct access file organization. Built with multiple platters which use both the top and bottom surfaces to read/write data. (Except for the top and bottom platter)


4 Disk is flexible and housed in a plastic case. Operates on the same principle of a hard disk. Has a single platter and is a convenient storage method. Advantages- Cheap, Reasonable capacity for text based storage Disadvantages- Slow access, limited storage, disk is easily dfamaged.

5 Allows data to be read from CD-ROMs Data cannot be altered, only read by a laser beam shining on the surface. Binary bit pattern is encoded at the time of production by a stamping process. The plastic surface is stamped with pit areas and land areas Pit areas absorb more laser light. Land Areas reflect more light. Changes between pit to land or visa versa represent binary ones and zeros.

6 Erasable optical disk that allows data to be read and written many times in a fashion much like the hard disk.

7 RAID- Redundant Array of Independent Disks Allows large amounts of storage that can be quickly accessed. Provides a range of protective features. Data written to a RAID disk is spread across a set of disks. Improves performance by taking advantage of parallel access across many disks.

8 Can be combined with disk mirroring which provides a fault tolerance feature. Disk mirroring- Data is written to multiple disks. Vital if the system needs continuous access.

9 Section 6.2.1

10 The Block size determines the # of bytes that are read and written in a single physical read or write operation on a hard disk. The Blocking Factor is usually more than one disk sector and is also known as cluster size.

11 A disk surface is divided into a # of circular tracks which are divided into sectors. Hard Disk Capacity is determined by the # of tracks per surface, # of sectors per track, and the # of bits or bytes per sector.

12 A floppy disk has a single platter with a top and bottom surface. A high density floppy has 160 tracks on 2 sides with 9 sectors per track and 512 bytes per sector. Capacity = # of surfaces X # of tracks X # sectors per track X bytes per sector Capacity = 2 surfaces X 160 tracks X 9 Sectors per track X 512 Bytes per sector =1,474,560 bytes

13 Data can be stored around the tracks in the sectors. Direct access is possible by specifying the require track and sector. In this way data is retrieved without reference to other related data. This is in contrast to sequential access. Data stored downwards in cylinders can be retrieved using a parallel technique utilizing multiple read /write heads.

14 Data is read and written to a disk sector by the use of read and write heads that are located on an arm. The heads can be fixed or moveable. Fixed read/write arms can read many sectors at oen time down the cylinder in a parallel operation. A moveable arm has one set of read/write heads which move across the surface of the disk.


16 Section 6.2.2

17 Made of two components- Seek Time and Latency Time ComponentSeek TimeLatency Time Alt. NamesWait Time ExplanationOccurs while the read/write arm seeks the desired track. Occurs while the head write arm waits for the desired sector on the track to spin around.

18 Access time can be specified as a relationship. Access time = track seek wait time + sector wait latency time Data on disks is accessed in times measured in terms of milliseconds. Slower than the processing speeds of CPUs. I/O is still slow and does not match the speed improvement of processors.

19 1. Outline how a disk drive operates. 2. Outline the role of the disk drive heads. 3. Define the term disk sector. 4. Define the term cylinder. 5. Define the term latency or rotational delay. 6. Define the term seek time. 7. Define the term access time. 8. How does seek time differ from access time? 9. Describe the access time to a hard disk with reference to the latency and seek times.

20 Section 6.3

21 An operating system (OS) is required for all general purpose computers to function. The OS controls the operation of the computer system by Managing the execution of programs Allocating resources Scheduling Controlling I/O operations Data management.

22 Allows operation of the CPU by one user or task. Example: MS DOS was a single user system in that only one user could use the system at any time.

23 Allows operation of the CPU by more than one user or task. The single CPU shares out its time between the demands of the users or tasks running at any one time.

24 Multiprocessing Allows the running of a program across a number of CPUs Allows a single user or task to run more than one program at the same time. A single user system can have this capability. Multitasking

25 Allows multiple parts of a single program to run at the same time.

26 Section 6.3.2

27 An OS must Handle program executions. Monitor input via input channels (keyboard, mouse) Control output (disk drives, printers, modems, display) Manage the file system: create, edit, delete, copy etc. Manage security measures: password checking and storage, access rights, disk space protection Manage memory allocation and swapping to ensure that clashed dont occur and nobodys area can be overwritten by another task or other users program. Manage the operation of virtual memory where a hard disk surface is used as a paging surface to expand memory

28 Provides basic function or performs a particular task Example: Copying data from one location to another.

29 Section 6.3.3

30 Combines compiled object code modules supplied by the programmer with programs from the runtime library of standard function modules. Example- I/O modules supplied by the programming environment to form.exe object code program. Initiated in Java by source code such as import* Replaces symbolic addresses. Link OS modules required to handle such issues as direct calls to the I/O system.

31 Copies linked object code into main memory for execution. Examples of an OS utility program.

32 Allows central library functions to manage the library functions used by the linker. Allows library functions to be added and compiled.

33 1. Define the term operating system. 2. Outline the key functions of an operating system. 3. Outline the functions of a linker. 4. Outline the functions of a loader. 5. Outline the functions of a library manager.

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