DistOS 2015W Session 3

Reading Response Discussion

Multics

Team: Sameer, Shivjot, Ambalica, Veena

It came into being in the 1960s and it completely vanished in 2000s. It was started by Bell, General Electric and MIT but Bell backed out of the project in 1969. Multics is a time sharing OS which provides Multitasking and Multiprogramming. It is not a Distributed OS but it a Centralized system which was written in the assembly language.

It provides following features:

1. Utility Computing
2. Access Control Lists
3. Single level storage
4. Dynamic linking
   • Sharded libraries or files can be loaded and linked to Random Access Memory at run time.
5. Hot swapping
6. Multiprocessing System
7. Ring oriented Security
   • It provides number of levels of authorization within the computer System.

Unix

Unix in its original conception is a small, minimal API system designed by two guys from Bell Labs. It was essentially a OS that would be easy to grasp for an programmer but not much beyond that. The UNIX OS ran on one computer, and terminals ran from that one computer. Thus it is not a distributed operating system as it is centralized and implements time sharing.

Sun NFS

The Sun NFS OS implemented networking using RPC connections. These connections are not secure. Sun wanted to encrypt these RPC connections but encryption would result in government regulations that Sun wanted to avoid in order to sell NFS over seas (See below).

   Sun wanted to encrypt their NFS system but decided not to. In the US encryption is regulated like munitions. Thus when Sun wanted to sell the NFS 
   system abroad they would have to contend with government regulations. To avoid these regulations, Sun decided to sell the unencrypted NFS system abroad.

Locus

1. Not scalable (They did not bother themselves about scalability. Locus ran only in five computers.)
   • Every computer stores a copy of every file
   • Also used CAS to manage files
2. Not efficient with abstractions
   • Trying to distribute files and processes
3. Allowed for process migration
4. Transparency
   • It provided network transparency to “disguise” its distributed context.

Sprite

Team: Jamie, Hassan, Khaled

Sprite had the following Design Features:

1. Network Transparency
2. Process Migration, file transfer between computers
   • User could initiate a process migration to an idle machine, and if the machine was no longer idle; due to it being used be another user, the system would take care of the process migration to another machine
3. Handling Cache Consistency
   • Sequential file sharing ==> By using a version number for each file
   • Concurrent write sharing ==> Disable cache to clients, enable write-blocking and other methods
4. Implemented a caching system that sped up performance
5. Implemented a log structured file system
   • Log structured file systems are optimized for writes; data is written to cache instead of memory, over reads. This is a way of minimizing the performance issues of doing writes
   • Example: SSD (Solid-state disks)

The main features to take away from the Sprite system is that it implemented a log structured file system, and implemented caching to increase performanace.