Multimedia and File System in OSs

Abstract

Silberschatz and Galvin (2009) explained that file system within any operating system provides the mechanism for storing and accessing a file contents which including data and programs. With the bulk storage that can exist in the secondary storage (the disk), the file system plays a big roles in maintaining such storage. To improve the efficiency of I/O in transferring files from the disk to the memory, the transformation is performed in units of blocks, where each block has one or more sectors and each sector can contains from 32 bytes to 4,096 bytes of information. On the other hand, file systems provides efficient access to the disk by allowing data to be stored, retrieved, and located easily. However, the file system faces two problems when it comes to dealing with files:

 

  • Defining how file system should look to the eyes of the users i.e. defining the file and its attributes, the operation allowed on the files and the directory structure that host such files.
  • Defining the algorithm and that data structure that can map the logical file system into the physical storage device (the disk).

 Once the above problems are tackled through the implementation of the file system design, the file system needs to only be able to issue generic commands to the appropriate device driver to read and write physical blocks on the disk (Silberschatz and Galvin, 2009).

Marshall (2001) explained that in modern computing systems, operating system are not only required to handle conventional data such as text files, programs and others via their file system implementation, but also to handle a new kind of data types such as multimedia data where data consist of continuous-media (such as audio and video) data as well as conventional files.

Characteristics of Multimedia Files

Silberschatz and Galvin (2009) explained that the term multimedia describes a wide range of applications that are in use in today’s modern computing systems and these include audio and video files, and most of the time multimedia files include a combination of both. As any data stored in the file system, multimedia data is no different, however, the only difference between the regular file and a multimedia file is that the multimedia file must be accessed at a specific timing. For example, the video file must be accessed from the file system at a rate that is consistent with the rate at which the video is being displayed. Such requirements that should be handled by the file system mechanism implemented within an operating system are known as a continuous-media data.

Silberschatz and Galvin (2009) also explained that in many occasion, the multimedia data can be delivered to the user from the local file system or from a remote server. In the first case where data is delivered from the local file, such delivery is called local playback. On the other hand, the multimedia files delivered to the user over the network is known as streaming. Some of the characteristics of multimedia systems are:

 

  • Multimedia files can be quite large.
  • Continuous media may require very high data rate.
  • Multimedia files/applications are very critical with timing delays during the playback.

Multimedia and File System

Galli (1999) explained that for computer systems to deliver continuous media data, it must provide the specific rate and timing requirements associated with such data known as quality of services. For the computing system to be able to deliver such requirements, several components with such system will be affected such as CPU scheduling, network managements, and disk scheduling; and some of such examples are:

 

  • Decoding and compression may require significant CPU processing.
  • Processes scheduling algorithm must change for multimedia tasks to meet the deadline requirements of continuous media.
  • File systems must be efficient to meet the rate requirements of continuous media.
  • Network protocols must support bandwidth requirements to support the streaming technique while minimizing delay in data transformation.

As a result of the characteristics described above, multimedia applications/files require levels of services from the operating system that differ from the traditional applications, such as spreadsheets or word processor. The most important fact of such requirements are the timing, and the rate where the playback of audio and video data demand that the data should be delivered within a certain deadline and at a continuous fixed rate. Such case with the traditional application is not valid since the time and the rate is not considered as constraints for such traditional files (Galli, 1999).

Silberschatz and Galvin (2009) explained that to provide the quality of service to the multimedia data, operating system often uses an admission control, which is a practice of admitting a request of service only if the system has sufficient resources to satisfy the request. Multimedia data (also known as continuous-media files) have two constraints that are not valid in the conventional data file: timing deadlines and rate requirements. To satisfy both constraints required by the multimedia data, disk scheduling algorithm must be optimized for such constraints. Also, these two constraints are usually in conflict with one another i.e. continuous-media files (multimedia files) require very high-disk bandwidth rates to satisfy such requirements, and disks usually have relatively low transfer rates and high latency rates, and to satisfy the requirements for multimedia data, disk schedulers must reduce the latency time to ensure high bandwidth.

Marshall(2001) explained that to satisfy the above challenges for the multimedia data, some of the following features are required in the modern computing systems:

 

  • High processing power – to deal with large data in the multimedia files, and deliver the data within the time constraints required to deliver in a real time.
  • Multimedia capable file system – needed to deliver the data within the time constraints.
  • Data representation/ file formats that support multimedia – multimedia data should have the format that can be easily handled, and also be able to be compressed- decompressed.
  • Efficient and high I/O – the file subsystems within the file system implemented within the operating system must be efficient and fast.
  • Special operating system – to be able to handle the file manipulation with multimedia data operating systems must provide the capabilities to access the file system and process data efficiently and quickly by providing the support for direct transfers to disk, fast interrupt processing, real-time scheduling, and I/O streaming.
  • Storage and memory – to handle multimedia data, large storage and large memory is required.

 Conclusion

Multimedia files/applications are in common use in the modern computing systems where the multimedia files include video and audio. The main distinction between multimedia data and conventional data is that multimedia data have a specific rate and deadline requirements that file systems have to handle within the operating system. That said, with such specific requirements with multimedia data, the data must be compressed before it is delivered to the user for playback (Dhamdhere, 2006).

Multimedia data may be delivered either from the local file system, or over the network using a technique known as streaming.

References

Dhamdhere, D. (2006) Operating Systems: A concept-based Approach. 2nd ed.London: McGraw Hill Higher Education.

Galli, D. (1999) Distributed Operating Systems: Concepts and Practice. 1st ed. NY:Prentice Hall.

Marshall, D. (2001) Multimedia Systems [Online]. Available from: http://www.cs.cf.ac.uk/Dave/Multimedia/node12.html (Accessed: 04 September 2010).

Silberschatz, A. & Galvin, P. (2009) Operating System Concepts. 8th ed. NJ: John Wiley & Sons, Inc.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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