Operating System Structure

• Command-Line Interface CLI
• Graphics User Interface GUI
• Touch-screen
• Batch processing 批处理

• Load a program into memory
• Run a program, and then end execution

• Read-Write

• Process exchange information

• Handle possible errors

• Many types of resources
  • CPU, main memory, file storage, I/O devices.

• keep track of which programs use how much and what kinds of computer resources

• Protection
  • Ensure that all access to system resources is controlled
• Security
  • Avoid attack from outside the system

• commands built-in 内建指令

• names of programs 程序名
• Advantage: adding new features doesn’t require modification of interpreter

• desktop metaphor (象征) interface
• Icons represent files, programs, actions, etc.

• Microsoft Windows is GUI with CLI “cmd” shell
• Apple Mac OS X is “Aqua” GUI interface with UNIX kernel underneath and shells available
• Unix and Linux have CLI with optional GUI interfaces

• Common API
  • Win32 API for Windows
  • POSIX API for POSIX-based systems (including virtually all versions of UNIX, Linux, and Mac OS X)
  • POSIX Portable Operating System Interface is – a family of standards specified by the IEEE Computer Society for maintaining compatibility between operating systems.
  • Java API for the Java virtual machine (JVM)

Standard C Library

• Contains functions which make system calls or do not make system calls makes programmers’ work much easier

Advantages of using Standard C Library

• It is simpler to call a function in a standard C library rather than to make a system call
• Portability
  • Source code executed in one OS can be run in another OS

Advantages of using system Calls

• System calls are usually more powerful than functions from the Standard C Library
  • Can create processes, share memory between processes, etc. These advanced features are not available in the Standard C Library.
• It’s a little bit faster than using a library function (since internally the library function uses a system call anyway).

Apps compiled on one system usually are not executable on other operating systems

• Each operating system provides its own unique system calls

How can apps be used in multi-operating systems

• Written in an interpreted language like Python, Ruby, and interpreter available on multiple operating systems解释性语言
• Written in a language that includes a VM containing the running app (like Java) 包括虚拟机的语言
• Written in a standard language (like C), compiled separately on each operating system to run on each OS 标准语言

Application Binary Interface (ABI) is
- about how different components of binary code can interface for a given operating system on a given architecture
- in low-level details
定义了不同的二进制代码组件如何在特定操作系统和特定础础架构上进行交互的低级别细节。

• Systems programs
• The kernel
  • Consists of everything below the system-call interface and above the physical hardware
  • Provides the file system, CPU scheduling, memory management, and other operating-system functions;
  • Consists of a large number of functions in one level

• High speed
• High efficiency

• changes in one component affect only that component, and no others
• Modules can be modified easily.

• The bottom layer (layer 0), is the hardware.
• The highest (layer N) is the user interface.
• Each layer is built on top of lower layers
  • With modularity, each layer uses functions (operations) and services of only lower-level layers

• extend to a microkernel
• port the operating system to new architectures