COMPUTER SYSTEM

COMPUTER SYSTEM

1. OPERATING SYSTEM

   • WHAT DOES IT DO?
     • CONTROL AND COORDINATE AMONG APPLICATIONS AND USERS
       • WHAT FOR?
         • EXECUTE USER PROGRAMS
         • MAKE SOLVING USER PROBLEMS EASIER
         • USE HARDWARE MORE EFFICIENTLY
       • HOW?
         • RESOURCE ALLOCATOR
           • MANAGES ALL RESOURCES
           • DECIDE BETWEEN CONFLICTING REQUESTS
             • EFFICIENT AND FAIR USE
         • CONTROL PROGRAM
           • CONTROLS EXECUTION OF PROGRAMS
             • PREVENT ERRORS
             • PREVENT IMPROPER USE OF COMPUTER
         • LIKE A GOVERNMENT
   • WHAT IS IT?
     • SPECIAL PROGRAM
       • LINK BETWEEN USER AND COMPUTER HARDWARE
   • KERNEL
     • ALWAYS RUNNING
     • SPECIAL PRIVELEGES
       • ACCESS SPECIAL INSTRUCTIONS
       • ACCESS SPECIAL MEMORY REGIONS
     • SYSTEM CALLS
       • LET USER PROGRAMS ACCESS KERNEL SERVICES
   • HARDWARE SUPPORT NEEDED
   • HOW TO RUN?
     • BOOTSTRAP PROGRAM
       • LOADED AT POWER-UP OR REBOOT
       • STORED IN ROM OR EPROM (FIRMWARE)
       • INITIALISE ENTIRE SYSTEM
       • LOAD KERNEL AND START EXECUTION
   • MODERN OS IS INTERRUPT DRIVER

2. HARDWARE

   • I/O
     • ACT AUTONOMOUSLY
     • DEVICES
       • CONCURRENT WITH CPU
     • CONTROLLERS
       • EACH IN CHARGE OF A DEVICE TYPE
       • EACH HAS A LOCAL BUFFER
         • WHERE CPU EXCHANGES DATA FROM/TO MAIN MEMORY
         • RECEIVE I/O FROM DEVICE
       • COORDINATE WITH CPU
         • INFORM FINISHED OPERATION
           • HOW?
             • INTERRUPT
               • TRANSFER CONTROL TO INTERRUPT SERVICE ROUTINE
                 • HOW?
                   • INTERRUPT VECTOR
                     • CONTAIN ADDRESSES OF ALL SERVICE ROUTINES
                   • INTERRUPT ARCHITECTURE
                     • SAVE ADDRESS OF INTERRUPTED INSTRUTION
               • INCOMING INTERRUPT
                 • DISABLED WHILE ANOTHER OF SAME OR HIGHER PRIORITY IS BEING PROCESSED
                   • PREVENT LOST INTERRUPT OR REENTRANCY PROBLEMS
               • TRAP
                 • WHAT IS IT?
                   • SOFTWARE-GENERATED INTERRUPT
                     • ERROR
                     • REQUEST BY USER CODE
                       • ALLOW USER PROGRAM TO INVOLE SYSTEM CALL
                         • CAREFULLY CONTROL ENTRY POINTS INTO KERNEL
               • TYPES OF INTERRUPT SYSTEM
                 • POLLING
                 • VECTORED
               • HANDLING DONE IN KERNEL MODE
                 • BY INTERRUPT HANDLER FOR DEVICE TYPE
   • CPU
     • DUAL MODE OPERATION
       • USER MODE
       • KERNEL MODE
     • ONE OR MORE
     • UPON INTERRUPT
       • STATE PRESERVED
         • HOW?
           • STORE REGISTERS AND PROGRAM COUNTERS
   • MEMORY
     • ACCESSED THROUGH COMMON BUS
       • CPUs, DEVICE CONTROLLERS
     • COMPETE FOR CYCLES
       • CONCURRENT EXECUTION OF CPUs AND DEVICES
     • STORAGE STRUCTURE
       • REGISTERS
         • FEW AND EXPENSIVE
         • INSIDE CPU
       • CACHE
         • MORE DATA THAN REGISTERS, BUT STILL SMALL
       • MAIN MEMORY
         • ONLY LARGE STORAGE THAT CPU CAN ACCESS DIRECTLY
       • SECONDARY STORAGE
         • EXTENSION OF MAIN MEMORY
         • PROVIDE LARGE NONVOLATILE STORAGE
       • MAGNETIC DISKS
         • RIGID METAL OR GLASS PLATTERS COVERED WITH MAGNETIC RECORDING MATERIAL
         • SURFACE LOGICALLY DIVIDED INTO TRACKS
           • TRACKS SUBDIVIDED INTO SECTORS
         • DISK CONTROLLER
           • DETERMINE LOGICAL INTERACTION BETWEEN DEVICE AND COMPUTER
     • STORAGE HIERARCHY
       • SPEED, COST, VOLATILITY
       • CACHING
         • COPY INFO INTO FASTER STORAGE SYSTEM
         • MAIN MEMORY = LAST CACHE FOR SECONDARY STORAGE
         • PERFORMED AT MANY LEVELS
         • IF INFO NOT IN CACHE, IT IS COPIED TO CACHE AND USED THERE
         • HIT RATIO = r, MISS ACCESS TIME = T, HIT ACCESS TIME = t
           • EFFECTIVE ACCESS TIME (EAT) = ?
       • MULTITASKING
         • MUST USE MOST RECENT VALUE, NO MATTER WHERE IT IS STORED IN THE HIERACHY
         • MULTIPROCESSOR ENVIRONMENT
           • MUST PROVIDE CACHE COHERENCY IN HARDWARE
             • ALL CPUs HAVE MOST RECENT VALUE IN THEIR CACHE
       • MOVEMENT BETWEEN LEVELS EITHER EXPLICIT OR IMPLICIT

3. APPLICATION PROGRAMS

   • DEFINE HOW SYSTEM RESOURCES ARE USED
   • WORD PROCESSORS, COMPILERS, WEB BROWSERS, DATABASE SYSTEMS, VIDEO GAMES

4. USERS

   • PEOPLE, MACHINES, OTHER COMPUTERS