Lecture 2: Systems Structures

Study Notes

Lecture 2: Systems Structures

The lecture is about systems structures, adapted from 8th edition textbook slides.
Topics covered include Operating System Services, User Interface, System Calls and their types, System Programs, OS Design and Implementation, and OS Structure.
Operating System services include user interface (varies between Command-Line Interface (CLI) and Graphics User Interface (GUI)), program execution, I/O operations, file system manipulation, communications, and error detection.
System calls are a programming interface to OS services, typically written in high-level languages (C or C++).
APIs (Application Programming Interfaces) are used by programs to access system calls. Common APIs include Win32 API, POSIX API, and Java API.
System calls copy file contents from one file to another using a sequence of calls.
System calls have various types like process control, file management, device management, information maintenance, communications, and protection.
System programs provide a convenient environment for program development and execution.
System programs can be user interfaces to system calls.
File management involves creating, deleting, copying, renaming, and generally managing files/directories.
System programs often provide status information, logging, debugging information, and other utilities.
Some systems use a registry for configuration information.
File modification involves text editors creating and modifying text files; special commands can also search text or perform transformations
Programming-language support includes compiling, assembling, and debugging using interpreters and loaders.
Program loading and execution (e.g., absolute loaders, relocatable loaders, linkage editors, overlay loaders, and debugging systems) are included within system programs.
System programs also handle communications among users and computer systems by enabling virtual connections (e.g., sending messages, browsing pages, email).
OS design and implementation aims to create a well-designed OS that is easy to modify and maintain.
OS design and implementation is often modular, with partitioning into smaller components rather than a monolithic system.
The user and system goals need to be considered in OS design. User goals include ease of use, ease of learning, reliability, safety, speed; system goals include ease of design, implementation, maintenance, and flexibility.
Principles like separating policy and mechanism in OS design are important.
OSes may be implemented using higher level languages (e.g., C or C++) or assembly language.
OS Structure involves common structures like simple structure, layered structure, microkernels, and modules.
Simple Structure, as seen in MS-DOS, is designed for minimal space use, but does not have well-separated functionality.
Layered Structure separates OS functionality into levels, like in Windows NT or similar OSes
Microkernel structures move parts of the kernel into "user" space, often using message-passing between modules.
The layered structure creates an overhead for calling every layer in a sequence, whereas modules address this via object-oriented methods.
Solaris uses a modular approach with different modules.
Examples of microkernel-based OSes include MINIX 3 and QNX.
Dynamically loadable modules (kernel extensions) are a feature of modern OS structures like Mac OS X, as well as others.
Virtualization (VM) takes the concept of layers to a higher level, allowing multiple operating systems to run within a physical computer.
Benefits of virtualization include sharing the same hardware to run multiple execution environments concurrently, protecting the host and VMs from each other, ease of testing different OSes during development, and server consolidation.
Examples of virtualization include VMware.
Homework assignments are assigned for additional learning.