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

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

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

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

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

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

Multiprocessor Operating - Contd SystemsHardware Concept

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

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.

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

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.

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

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.

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

Comparison between Systems

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.

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

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