Operating Systems Study Guide PDF

**Lesson 3: Introduction of Operating System** - What Operating Systems Do - Computer-System Organization - Computer-System Architecture - Operating-System Operations - Resource Management - Security and Protection - Virtualization - Distributed Systems - Kernel Data Struc...

**Lesson 3: Introduction of Operating System** - What Operating Systems Do - Computer-System Organization - Computer-System Architecture - Operating-System Operations - Resource Management - Security and Protection - Virtualization - Distributed Systems - Kernel Data Structures - Computing Environments - Free/Libre and Open-Source Operating Systems **Computer System Structure** Computer system can be divided into four components: - Hardware -- provides basic computing resources - CPU, memory, I/O devices - Operating system - Controls and coordinates use of hardware among various applications and users - Application programs -- define the ways in which the system resources are used to solve the computing problems of the users - Word processors, compilers, web browsers, database systems, video games - Users - People, machines, other computers **What Operating Systems Do** - Depends on the point of view - Users want convenience, **ease** **of** **use** and **good performance** - Don't care about **resource** **utilization** - But shared computer such as **mainframe** or **minicomputer** must keep all users happy - Operating system is a **resource allocator** and **control program** making efficient use of HW and managing execution of user programs - Users of dedicate systems such as **workstations** have dedicated resources but frequently use shared resources from **servers** - Mobile devices like smartphones and tables are resource poor, optimized for usability and battery life - Mobile user interfaces such as touch screens, voice recognition - Some computers have little or no user interface, such as embedded computers in devices and automobiles - Run primarily without user intervention **Defining Operating Systems** Term OS covers many roles - Because of myriad designs and uses of OSes - Present in toasters through ships, spacecraft, game machines, TVs and industrial control systems - Born when fixed use computers for military became more general purpose and needed resource management and program control - No universally accepted definition - "Everything a vendor ships when you order an operating system" is a good approximation - But varies wildly - "The one program running at all times on the computer" is the **kernel,** part of the operating system - Everything else is either - a **system program** (ships with the operating system, but not part of the kernel) , or - an **application program**, all programs not associated with the operating system - Today's OSes for general purpose and mobile computing also include **middleware** -- a set of software frameworks that provide addition services to application developers such as databases, multimedia, graphics **Computer System Organization** Computer-system operation - One or more CPUs, device controllers connect through common **bus** providing access to shared memory - Concurrent execution of CPUs and devices competing for memory cycles  **Computer-System Operation** - I/O devices and the CPU can execute concurrently - Each device controller is in charge of a particular device type - Each device controller has a local buffer - Each device controller type has an operating system **device driver** to manage it - CPU moves data from/to main memory to/from local buffers - I/O is from the device to local buffer of controller - Device controller informs CPU that it has finished its operation by causing an **interrupt** **Common Functions of Interrupts** - Interrupt transfers control to the interrupt service routine generally, through the **interrupt** **vector**, which contains the addresses of all the service routines - Interrupt architecture must save the address of the interrupted instruction - A **trap** or **exception** is a software-generated interrupt caused either by an error or a user request - An operating system is **interrupt driven** **Interrupt Timeline** **Computer Startup** - **bootstrap program** is loaded at power-up or reboot - Typically stored in ROM or EPROM, generally known as **firmware** - Initializes all aspects of system - Loads operating system kernel and starts execution **Interrupt Handling** - The operating system preserves the state of the CPU by storing registers and the program counter - Determines which type of interrupt has occurred: - **polling** - **vectored** interrupt system - Separate segments of code determine what action should be taken for each type of interrupt **Interrupt-drive I/O Cycle** **I/O Structure** - After I/O starts, control returns to user program only upon I/O completion - Wait instruction idles the CPU until the next interrupt - Wait loop (contention for memory access) - At most one I/O request is outstanding at a time, no simultaneous I/O processing - After I/O starts, control returns to user program without waiting for I/O completion - **System call** -- request to the OS to allow user to wait for I/O completion - **Device-status table** contains entry for each I/O device indicating its type, address, and state - OS indexes into I/O device table to determine device status and to modify table entry to include interrupt **Storage Structure** - Main memory -- only large storage media that the CPU can access directly - **Random** **access** - Typically **volatile** - Typically **random-access memory** in the form of **Dynamic Random-access Memory (DRAM)** - Secondary storage -- extension of main memory that provides large **nonvolatile** storage capacity - **Hard Disk Drives** (**HDD**) -- rigid metal or glass platters covered with magnetic recording material - Disk surface is logically divided into **tracks**, which are subdivided into **sectors** - The **disk controller** determines the logical interaction between the device and the computer - **Non-volatile memory (NVM)** devices-- faster than hard disks, nonvolatile - Various technologies - Becoming more popular as capacity and performance increases, price drops **Storage Definitions and Notation Review** The basic unit of computer storage is the **bit**. A bit can contain one of two values, 0 and 1. All other storage in a computer is based on collections of bits. Given enough bits, it is amazing how many things a computer can represent: numbers, letters, images, movies, sounds, documents, and programs, to name a few. A **byte** is 8 bits, and on most computers, it is the smallest convenient chunk of storage. For example, most computers don't have an instruction to move a bit but do have one to move a byte. A less common term is **word**, which is a given computer architecture's native unit of data. A word is made up of one or more bytes. For example, a computer that has 64-bit registers and 64-bit memory addressing typically has 64-bit (8-byte) words. A computer executes many operations in its native word size rather than a byte at a time. Computer storage, along with most computer throughput, is generally measured and manipulated in bytes and collections of bytes. A **kilobyte**, or KB, is 1,024 bytes; a **megabyte**, or **MB**, is 1,024^2^ bytes; a **gigabyte**, or GB, is 1,024^3^ bytes; a **terabyte**, or **TB**, is 1,024^4^ bytes; and a **petabyte**, or **PB**, is 1,024^5^ bytes. Computer manufacturers often round off these numbers and say that a megabyte is 1 million bytes and a gigabyte are 1 billion bytes. Networking measurements are an exception to this general rule; they are given in bits (because networks move data a bit at a time). **Storage Hierarchy** - Storage systems organized in hierarchy - Speed - Cost - Volatility - **Caching** -- copying information into faster storage system; main memory can be viewed as a cache for secondary storage - **Device Driver** for each device controller to manage I/O - Provides uniform interface between controller and kernel  **How a Modern Computer Works** **Direct Memory Access Structure** - Used for high-speed I/O devices able to transmit information at close to memory speeds - Device controller transfers blocks of data from buffer storage directly to main memory without CPU intervention - Only one interrupt is generated per block, rather than the one interrupt per byte **Computer-System Architecture** - Most systems use a single general-purpose processor - Most systems have special-purpose processors as well - **Multiprocessors** systems growing in use and importance - Also known as **parallel systems**, **tightly-coupled systems** - Advantages include: - **Increased throughput** - **Economy of scale** - **Increased reliability** -- graceful degradation or fault tolerance - Two types: - **Asymmetric Multiprocessing** -- each processor is assigned a specie task. - **Symmetric Multiprocessing** -- each processor performs all tasks **Symmetric Multiprocessing Architecture**  **A Dual-Core Design** - Multi-chip and **multicore** - Systems containing all chips - Chassis containing multiple separate systems **Non-Uniform Memory Access System**  **Clustered Systems** - Like multiprocessor systems, but multiple systems working together - Usually sharing storage via a **storage-area network (SAN)** - Provides a **high-availability** service which survives failures - **Asymmetric clustering** has one machine in hot-standby mode - **Symmetric clustering** has multiple nodes running applications, monitoring each other - Some clusters are for **high-performance computing (HPC)** - Applications must be written to use **parallelization** - Some have **distributed lock manager** (**DLM**) to avoid conflicting operations **PC Motherboard**  **Operating-System Operations** - Bootstrap program -- simple code to initialize the system, load the kernel - Kernel loads - Starts **system daemons** (services provided outside of the kernel) - Kernel **interrupt driven** (hardware and software) - Hardware interrupt by one of the devices - Software interrupt (**exception** or **trap):** - Software error (e.g., division by zero) - Request for operating system service -- **system call** - Other process problems include infinite loop, processes modifying each other or the operating system **Multiprogramming and Multitasking** - **Multiprogramming** (**Batch system**) needed for efficiency - Single user cannot keep CPU and I/O devices busy at all times - Multiprogramming organizes jobs (code and data) so CPU always has one to execute - A subset of total jobs in system is kept in memory - One job selected and run via **job scheduling** - When it has to wait (for I/O for example), OS switches to another job - **Timesharing** (**multitasking**) is logical extension in which CPU switches jobs so frequently that users can interact with each job while it is running, creating **interactive** computing - **Response time** should be \< 1 second - Each user has at least one program executing in memory **process** - If several jobs ready to run at the same time **CPU scheduling** - If processes don't fit in memory, **swapping** moves them in and out to run - **Virtual memory** allows execution of processes not completely in memory **Memory Layout for Multiprogrammed System** **Dual-mode and Multimode Operation** - **Dual-mode** operation allows OS to protect itself and other system components - **User mode** and **kernel mode** - **Mode bit** provided by hardware - Provides ability to distinguish when system is running user code or kernel code - Some instructions designated as **privileged**, only executable in kernel mode - System call changes mode to kernel, return from call resets it to user - Increasingly CPUs support multi-mode operations - i.e. **virtual machine manager** (**VMM**) mode for guest **VMs**