Some Basic Computer Organization

• This is 1.2 - 1.4 of the book.
  • You should read.
• Book definitions:
  • A CPU is the central processing unit.
    • This is the device we studied in Architecture.
    • This is the device that executes instructions.
  • A Processor is a chip that contains one or more CPUs
  • A Core is the basic computational unit of a CPU.
  • Multicore is a device that contains multiple cores.
  • Multiprocessor is a device that contains multiple processors.
• Today most processors are multicore.
• But most computers are not multiprocessor.
• But the OS can make it look like
  • A single core is actually multiple cores
  • A multiprocessor and a multicore machine are the same.
• So we tend to get sloppy with these terms.
• It is probably easier to think in terms of a single core/CPU until we need to do otherwise.
• A bus is a communications device
  • There are many different busses in a system.
    • Inside a CPU is a bus that connects the components (pc, alu, cu, ir, mmu, registers).
    • There may be one or more system busses that connect higher level components (keybord/mouse, monitor, memory, disks).
    • This depends on the hardware.
• The devices mentioned above have a device controller
  • This is the hardware interface to the device.
  • It is connected to the bus.
  • There is a defined protocol on how to interact with that device.
  • For example (totally made up by me)
    • Put a 32 bit address on the address line
    • Put a 1 on the read line for 4ns
    • 32 bits of data will be placed on the data line 5ns later.
    • Place a 0 on the read line.
  • These most likely have a primitive/simple cpu and a hard coded os!
• A device driver is a program that understands how to control a device.
  • These are typically subroutines of the kernel.
  • These provide the OS with a uniform interface to the devices.
  • On unix/linux everything is a "file".
  • Device drivers allow the OS to be extended to add new devices.
  • The device driver may have to allow for complex/parallel devices
  • The book gives the example of a USB hub, which might have multiple devices.
  • So they may have to deal with parallel access and device synchronization.
• We discussed the memory hierarchy in Architecture.
• Figure 1.6 has a more detailed version of this.
  • volatile memory is memory that is erased when the power is turned off
    • Think RAM
  • non-volatile memory is not.
    • Think hard drive, optical disk, tapes, ...
    • But also ROM
• We can now discuss "computers"
  • A single core general purpose computer is extremely rare.
    • My exceedingly low cost phone has
      • 2x2.2 GHz Cortex A76
      • 6x2.0 GHz Cortex A55
      • And a GPU (Mali-G57 MC2)
  • This is a multiprocessor system.
  • There are two basic types of multiprocessors
    • Symmetric Multiprocessors (SMP)
      • All processors share the same memory.
      • See figure 1.8
      • Generally most high level OSs support SMP
      • (linux run top, press 1)
    • Non Uniform memory access (NUMA)
      • Each processor has its own memory.
      • See figure 1.10
  • The os needs to control memory access.
  • A multiprocessor system is usually in a single "box".
  • Connecting multiple "boxes" together forms a distributed system or a cluster
    • This allows
      • High availability
      • Fault tolerance and recovery.
      • High performance computing.
    • The os can be as little as
      • Individual OS on the computers.
      • A program that does the communications, data movement and computations.
    • Or a tightly coupled distributed OS that looks like a single interface.