ENVS 1800 Lecture Notes - Lecture 13: Network Operating System
14 May 2018
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ENVS 1800 Tutorial 13 Notes – Network operating system services, OS Protocol Support and
Other Services
Introduction
Network operating system services
• Even though a bit of time is wasted returning the head to its original position
• The other change is to maintain two separate queues.
• Once the head has started to traverse the disk, it will read only blocks that were already
waiting when the traverse started.
• This prevents block requests that are just ahead of the head from jumping into the
queue.
• Instead, such a block would be placed in the alternate queue to wait for the next pass.
• This approach is fairer to requests that have already been waiting.
• Practically, there is no reason to move the head beyond the last block sought, and
reversal will take place at that time.
• Some writers refer to this as c-look scheduling.
• The head movement for different scheduling algorithms
• These drawings, based on an example and drawings by Silberschatz et al. [SILB08],
assume a disk queue containing blocks in tracks 98, 183, 37, 122, 14, 124, 65, and 67.
• The head starts at track 53.
• To take advantage of networking, the operating system must include services that
support networking and provide the features offered by networking capability.
• These services include implementation of network software protocols, augmentation of
the file system to support the transfer and use of files from other locations, remote
login capability, and additional utilities and tools.
• Modern operating systems include networking facilities as part of the base system.
OS Protocol Support and Other Services
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