Құрастырушы: Құрастырушылар: аға оқытушы Успанова А. И

After this lesson, you should be able to write essay (about 250 words):

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  Future operating systems.
  

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  Low-level device control (initiate a disk read, etc.).
  
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  Higher-level abstractions (files, databases, etc.).
  
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  The OS may provide different levels of disk access to different clients.
  
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  Physical disk (surface, cylinder, sector).
  
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  Logical disk (disk block).
  
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  Logical file (file block, record, or byte).
  

Figure 26 - Physical Disk Structure

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  Platters.
  
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  Surfaces.
  
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  Tracks.
  
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  Sectors.
  
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  Cylinders.
  
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  Arm.
  
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  Heads.
  

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  Cylinder, surface, track, sector, transfer size…Older disks required the OS to specify all of this.
  
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  The OS needed to know all disk parameters. Modern disks are more complicated
  
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  Not all sectors are the same size, sectors are remapped, etc. Current disks provide a higher-level interface (SCSI).
  
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  The disk exports its data as a logical array of blocks [0…N].
  
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  Disk maps logical blocks to cylinder/surface/track/sector.
  
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  Only need to specify the logical block # to read/write.
  
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  But now the disk parameters are hidden from the OS.
  

We use the term data processing system to include the resourc­es that are used to accomplish the processing of data. There are four types of resources: people, materials, facilities, and equip­ment. People provide input to computers, operate them, and use their output. Materials, such as boxes of paper and printer rib­bons, are consumed in great quantity. Facilities are required to house the computer equipment, people and materials.

The need for converting facts into useful information is not a phenomenon of modern life. Throughout history, and even prehistory, people have found it necessary to sort data into forms that were easier to understand. For example, the ancient Egyp­tians recorded the ebb and flow of the Nile River and used this information to predict yearly crop yields. Today computers con­vert data about land and water into recommendations to farm­ers on crop planting. Mechanical aids to computation were de­veloped and improved upon in Europe, Asia, and America throughout the seventeenth, eighteenth, and nineteenth centu­ries. Modern computers are marvels of an electronics technol­ogy that continues to produce smaller, cheaper, and more pow­erful components.

Basic data processing operations. Five basic operations are characteristic of all data process­ing systems: inputting, storing, processing, outputting, and con­trolling. They are defined as follows.

Inputting is the process of entering data, which are collected facts, into a data processing system. Storing is saving data or information so that they are available for initial or for additional processing. Processing represents performing arithmetic or logical operations on data in order to convert them into useful in­formation. Outputting is the process of producing useful infor­mation, such as a printed report or visual display. Controlling is directing the manner and sequence in which all of the above operations are performed.

Data storage hierarchy. It is known that data, once entered, are organized and stored in successively more comprehensive groupings. Generally, these groupings are called a data storage hierarchy. The general group­ings of any data storage hierarchy are as follows.

1) Characters, which are all written language symbols: let­ters, numbers, and special symbols. 2) Data elements, which are meaningful collections of related characters. Data elements are also called data items or fields. 3) Records, which are collections of related data elements. 4) Files, which are collections of re­lated records. A set of related files is called a data base or a data bank.

1. What is processing? 2. What is data processing? 3. What does the term of data processing system mean? 4. What basic operations does a data processing system include? 5. What is inputting /storing / outputting information? 6. What do you understand by resources? 7. How did ancient Egyptians convert facts into useful information? 8. When were mechanical aids for computation developed? 9. What does data storage hierarchy mean? 10. What are the general groupings of any data storage hierarchy?

Figure 27 - Data Processing Cycle

The activity of data processing can be viewed as a "system". According to James O'brien a system can be defined as "a group of interrelated components that seeks the attainment of a common goal by accepting inputs and producing outputs in an organised process". For example, a production system accepts raw material as input and produces finished goods as output.

Figure 28 – Information process

Disk Parameters:

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  Form factor: 3.5”
  
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  Capacity: 750 GB
  
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  Rotation rate: 7,200 RPM
  
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  Platters: 4
  
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  Surfaces: 8
  
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  Sector size: 512 bytes
  
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  Cache: 16MB
  
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  Transfer rate: 40 MB/s (inner) – 78 MB/s (outer)
  
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  Average seek: 9.5 ms
  

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  When the OS uses the disk, it tries to minimize the cost of all of these steps.
  
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  Particularly seeks and rotation.
  

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  Reasonable when load is low.
  
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  Long waiting times for long request queues SSTF (shortest seek time first).
  
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  Minimize arm movement (seek time), maximize request rate.
  
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  Favors middle blocks SCAN (elevator).
  
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  Service requests in one direction until done, then reverse C-SCAN.
  
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  Like SCAN, but only go in one direction (typewriter).
  

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  Implement an abstraction (files) for secondary storage.
  
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  Organize files logically (directories).
  
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  Permit sharing of data between processes, people, and machines.
  
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  Protect data from unwanted access (security).
  
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  A file is data with some properties
  
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  Contents, size, owner, last read/write time, protection, etc.
  
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  A file can also have a type.
  

Understood by the file system. Block, character, device, portal, link, etc.

Understood by other parts of the OS or runtime libraries. Executable, dll, souce, object, text, etc.

A file’s type can be encoded in its name or contents Windows encodes type in name .com, .exe, .bat, .dll, .jpg and etc. Unix encodes type in contents. Magic numbers, initial characters (e.g., #! for shell scripts).

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  For users, they provide a structured way to organize files
  
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  For the file system, they provide a convenient naming interface that allows the implementation to separate logical file organization from physical file placement on the disk.
  

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  Naming hierarchies (/, /usr, /usr/local/, …)
  

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  Easy to do on a single machine.
  
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  PCs, workstations, and networks get us there (mostly)
  

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  Basis for communication and synchronization.
  

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  Semantics of concurrent access.
  
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  Protection.