1. Types of Operating Systems
Computer Engineering Department
Distributed Systems Course
Asst. Prof. Dr. Ahmet Sayar
Kocaeli University - Fall 2014

2. Uniprocessor Operating Systems
An OS acts as a resource manager or an arbitrator
Manages CPU, I/O devices, memory
OS provides a virtual interface that is easier to use than hardware
Structure of uniprocessor operating systems
Monolithic (e.g., MS-DOS, early UNIX)
One large kernel that handles everything
Layered design
Functionality is decomposed into N layers
Each layer uses services of layer N-1 and implements new service(s) for layer N+1

3. Uniprocessor Operating Systems
Microkernel architecture
Small kernel
user-level servers implement additional functionality

4. Distributed Operating System -Multi-computer-
Manages resources in a distributed system
Seamlessly and transparently to the user
Looks to the user like a centralized OS
But operates on multiple independent CPUs
Provides transparency
Location, migration, concurrency, replication,…
Presents users with a virtual uniprocessor
Harder to develop and handle compared to multi-processor os
-memory is not shared
-communication is done through messaging
-no simple system-wide synch mechanism

5. Multi-computer Systems
How to run multiprocessor software on multicomputer systems ?

6. Multiprocessor Operating Systems
Multi-core
Like a uniprocessor operating system
Manages multiple CPUs transparently to the user
Shared main memory and controlled by a single OS instance
Each processor has its own hardware cache
Maintain consistency of cached data
involves a multiprocessor computer hardware architecture where two or more identical processors are connected to a single shared main memory and are controlled by a single OS instance

7. Multiprocessor Operating - Contd SystemsHardware Concept

8. Multiprocessor Operating Systems -Contd
A bus-based multiprocessor
A representation of shared memory super computing

9. Distributed Operating Systems (1)
Example: MOSIX cluster - single system image
Processors variously called nodes, computers, machines, hosts
Distributed operating system services: gives illusion of single system
A distributed operating system is the logical aggregation of operating system software over a collection of independent, networked, communicating, and spatially disseminated computational nodes. individual system nodes each hold a discrete software subset of the global aggregate operating system.
The microkernel and the management components collection, work together. They support the global system’s goal of seamlessly integrating all network-connected resources and processing functionality into an efficient, available, and unified system. This seamless integration of individual nodes into a global system is referred to as transparency, or single system image; describing the illusion provided to users of the global system’s appearance as a singular and local computational entity.

10. Distributed Operating Systems (2)
Gives illusion of single system
Users not aware of multiplicity of machines
Access to remote resources similar to access to local resources
Data Migration – transfer data by transferring entire file, or transferring only those portions of the file necessary for the immediate task
Computation Migration – transfer the computation, rather than the data, across the system

11. Network Operating System (1)
Watch out the difference between distributed operating system (previous slide) and network operating system (this slide)
Here you are exposing presence of multiple machines to the application
A networking operating system (NOS) is the software that runs on a server and enables the server to manage data, users, groups, security, applications, and other networking functions. The network operating system is designed to allow shared file and printer access among multiple computers in a network, typically a local area network (LAN), a private network or to other networks. The most popular network operating systems are Microsoft Windows Server 2008, UNIX and Linux.

12. Network Operating System (2)
Users are aware of multiplicity of machines. Access to resources of various machines is done explicitly by:
Remote logging into the appropriate remote machine (telnet, ssh)
Remote Desktop (Microsoft Windows)
Transferring data from remote machines to local machines, via the File Transfer Protocol (FTP) mechanism

13. Middleware-based Systems
This is actually combination of distributed operating system services (1) and network operating system (2)
Middleware is hiding the presence of multiple machines, the complexity that the application needs to handle is put into the middle layer
In an open middleware-based distributed system, the protocols used by each middleware layer should be the same, as well as the interfaces they offer to applications. This is a much higher level of abstraction than (for instance) the NOS Socket API.

14. Types of Distributed OSs
System
Description
Main Goal
DOS
Tightly-coupled operating system for multiprocessors and homogeneous multicomputers
Hide and manage hardware resources
NOS
Loosely-coupled operating system for
heterogeneous multicomputers (LAN and WAN)
Offer local services to remote clients
Middleware
Additional layer atop of NOS implementing general purpose services
Provide distribution transparency
DOS: Distributed Operating Systems
NOS: Network Operating Systems

15. Comparison between Systems

16. Pitfalls when Developing Distributed Systems
False assumptions made by first time developer:
The network is reliable.
The network is secure.
The network is homogeneous.
Latency is zero.
Bandwidth is infinite.
Transport cost is zero.
There is one administrator.

17. Summary Distributed Systems … autonomous computers
working together to give the appearance of a single, coherent system.
They are transparent, scalable and open.
Unfortunately, they also tend to be complex

18. Overview challenges Concurrency Openness Security
Shared access to resources must be possible
Openness
Interfaces should be publicly available to ease adding new components
Security
The system should only be used in the way intended