Objectives

Notes

• Types of Architectures
  • A cpu is the central processing unit.
  • A computer may have one or more cpus
  • Each CPU may have one or more cores
  • Single processor systems generally have a single core.
    • These are probably hard to find in general purpose computers these days
    • But they exist.
  • Multiprocessor systems come in a variety of configurations.
    • Multicore single processors are symmetric multiprocessors
      A single shared memory, which everything has access to.
    • This could also be accomplished by multiple cpus
    • The big idea is that all memory is shared and equally accessible.
      • This makes it simpler to pass data between processors/processes
    • Local cores/processors do have their own cache
      • So we would like to keep processes on the same core/cpu
    • Other configurations could include
      • Non - uniform memory access - NUMA
      • Clusters or other distributed systems.
    • Generally memory/data exchange is complicated
      • because a slower bus or network is involved
      • And because more cooperation between processors is required.
  • So what do operating systems do?
    • We have partially answered this
    • But
      • Initial system startup
        • bios/UART -> Kernel -> Kernel Daemons -> systemd (Running System.)
      • We have discussed hardware interrupts (ie someone connecting via the network )
        • But there are also software interrupts (system calls/exceptions) which might cause an action.
      • In any case, the OS needs to support the creation, scheduling, execution and termination of programs.
      • It migh also need to handle process tasks such as
        • migration between cpus
        • Communications between processes
      • Multiprogramming - allowing a queue of programs so that when one needs to pause for resources another can be run
        • This is to fully utilize the cpu/cpus/cores ...
      • Multitasking - allowing the illusion that all programs are running simultaneously, even when the number of programs exceeds the number of cores.
      • Allocating and sharing memory between processes, and even protecting the memory a process has from other processes.
      • Providing a file system on removable media.
      • Providing protection /security
        • Most cpus support at least two modes of operation
        • And this is supported at the os level as well
        • See the picture on page 25
      • Supporting timers
        • A hardware element that operates independently of instruction execution
        • Can raise an interrupt
    • Resources managed
      • Processes
      • Memory
      • File system
      • I/O
      • Security