Chapter 1: Intro of OS

Chapter 1: Intro of OS

1. Operating System - A program that acts as an intermediary between a user of a computer and the computer hardware

   • Goals of the OS
     • 1. Execute user programs and make solving user problems easier
     • 2. Make the computer system convenient to use
     • 3. Use the computer hardware in an efficient manner
   • Interrupt Driven
     • Hardware
       • a device may trigger an interrupt by sending a signal to the CPU, usually by way of the system bus.
     • Software
       • a program may trigger an interrupt by executing a special operation called a system call.
     • When an interrupt occurs, the operating system preserves the state of the CPU by storing the registers and the program counter

2. Computer System Structure

   • Hardware
   • Operating System
   • Application Programs
   • Users
   • Computer System Organization
     • modern computer has at least 1 CPU & a # of device controllers connected through a common bus that provides access to shared memory
       • CPU moves data from/to main memory to/from local buffers
         • CPU and the device controllers can execute in parallel, competing for memory cycles. To ensure orderly access to the shared memory, a memory controller synchronizes access to the memory
           • Storage Structure
             • Main memory – the only large storage media that the CPU can access directly
               • Random access Typically volatile
               • 1. too small to store all needed data and programs permanently
                 • 2. bc volatile ... loses its contents wen powered off
             • Secondary storage – extension of main memory that provides large nonvolatile storage capacity
               • Ex: Hard disks
             • Storage Hierarchy
     • Each device controller is in charge of a specific type of device (i.e, disk drives, audio devices, or video displays). Each device controller has a local buffer
     • I/O Structure
       • Interrupt Driven
         • start an I/O op: device driver loads appropriate registers within the device controller
           • device controller examines the contents of these registers to determine what action to take (ex. “read” a character from keyboard)
             • controller starts transfer of data from device to its local buffer.
               • Once the transfer of data is complete, device controller informs device driver it's done via an interrupt
                 • device driver returns control to the operating system, returning data or a pointer to the data if the operation was a read, or status
         • fine for moving small amounts of data BUT can produce high overhead when used for bulk data movement such as disk I/O.
           • Direct Memory Access (DMA)
             • sets up buffers, pointers, & counters for the I/O device, then device controller transfers an entire BLOCK of data directly to or from its own buffer storage to memory, with no intervention by the CPU.
               • Only 1 interrupt is generated per block, to tell device driver that operation is done. While the device controller's performing these ops, CPU is available to do other work
     • Architecture
       • Single-processor Systems
       • Multiprocessor Systems
         • Advantages
           • 1. increased throughput (more work done in less time)
             • 2. economy of scale (bc they share power, storage etc.)
               • 3. increased reliability (failure of 1 processor wont halt entire system, will just slow it down)
     • OS Structure
       • Multiprogramming
         • batch systems
           • One job selected and run via job scheduling
             • When it has to wait (for I/O for example), OS switches to another job
         • timesharing systems (multitasking)
           • Each user has at least one process executing .
             • If several processes are ready to run at the same time, we need to have CPU scheduling
             • Virtual memory allows execution of processes not completely in memory

3. Process Management

   • Process needs CPU, memory, I/O, files, etc. Initialization data to accomplish its task
   • Process termination requires reclaim of any reusable resources
   • Single-threaded
     • Instructions are executed sequentially, one at a time, until completion
   • Multithreaded
     • process has one program counter per thread
   • OS is responsible for
     • Creating and deleting both user and system processes
     • Suspending and resuming processes
     • Providing mechanisms for process synchronization
     • Providing mechanisms for process communication
     • Providing mechanisms for deadlock handling

4. Memory Managment

   • Keeping track of which parts of memory are currently being used and by whom
   • Deciding which processes (or parts thereof) and data to move into and out of memory
   • Allocating and deallocating memory space as needed

5. Storage Managment

   • File Storage
     • 1. Disk 2. Flash Memory 3. Tape
       • Each medium is controlled by device drivers (i.e., disk drive, tape drive)
   • Creating and deleting files and directories
   • Mapping files onto secondary storage
   • Primitives to manipulate files and directories
   • Backup files onto stable (non-volatile) storage media

Images and files in the map