uni/year2/semester1/logseq-stuff/pages/Overview of Computer Systems.md

• #CT213 - Computer Systems & Organisation
• No previous topic.
• Relevant Slides:

• Traditional Classes of Computer Systems

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  • What is a Personal Computer (PC)? card-last-score:: 5 card-repeats:: 2 card-next-schedule:: 2022-09-23T18:28:00.836Z card-last-interval:: 4 card-ease-factor:: 2.7 card-last-reviewed:: 2022-09-19T18:28:00.836Z
    • A Personal Computer is a computer designed for use by an individual, usually incorporating a graphics display, a keyboard, and a mouse.
  • What is a Server? #card card-last-interval:: 41.44 card-repeats:: 5 card-ease-factor:: 2.18 card-next-schedule:: 2022-12-22T21:33:20.708Z card-last-reviewed:: 2022-11-11T11:33:20.709Z card-last-score:: 5
    • A server is a computer used for running larger programs for multiple users, often simultaneously, and typically accessed only via a network.
  • What is a Supercomputer? card-last-interval:: 11.2 card-repeats:: 3 card-ease-factor:: 2.8 card-next-schedule:: 2022-10-14T15:37:52.646Z card-last-reviewed:: 2022-10-03T11:37:52.647Z card-last-score:: 5
    • A supercomputer is a member of a class of computers with the highest performance (and cost). They are configured as servers and typically cost tens to hundreds of millions of dollars.
  • What is an Embedded Computer? #card card-last-interval:: 33.64 card-repeats:: 4 card-ease-factor:: 2.9 card-next-schedule:: 2022-12-18T07:45:01.338Z card-last-reviewed:: 2022-11-14T16:45:01.338Z card-last-score:: 5
    • An embedded computer is a computer inside another device, used for running one predetermined application or collection of software.
  • What are Personal Mobile Devices? card-last-interval:: 11.2 card-repeats:: 3 card-ease-factor:: 2.8 card-next-schedule:: 2022-10-12T21:31:08.211Z card-last-reviewed:: 2022-10-01T17:31:08.211Z card-last-score:: 5
    • Personal Mobile Devices are small, wireless devices that connect to the internet.
    • They rely on batteries for power, and software is installed by downloading apps.
    • Conventional examples include smartphones and tablets.
  • What is Cloud Computing? #card card-last-interval:: 29.26 card-repeats:: 4 card-ease-factor:: 2.66 card-next-schedule:: 2022-12-13T22:41:13.223Z card-last-reviewed:: 2022-11-14T16:41:13.223Z card-last-score:: 5
    • Cloud Computing refers to large collections of servers that provide services over the internet.
    • Some providers rent dynamically varying number of servers as a utility.
  • What is Software as a Service? #card card-last-interval:: 29.26 card-repeats:: 4 card-ease-factor:: 2.66 card-next-schedule:: 2022-12-13T22:47:42.790Z card-last-reviewed:: 2022-11-14T16:47:42.790Z card-last-score:: 5
    • Software as a Service delivers software & data as a service over the internet, usually via a thing program, such as a browser.
    • Examples include web search & email.

• Computer Systems

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  • What is Application Software? #card card-last-interval:: 33.64 card-repeats:: 4 card-ease-factor:: 2.9 card-next-schedule:: 2022-12-18T07:45:07.567Z card-last-reviewed:: 2022-11-14T16:45:07.567Z card-last-score:: 5
    • Application Software consists of user-installed applications & programs.
    • Application Software provides services to the user that are commonly useful.
  • What is the purpose of the Operating System? #card card-last-interval:: 49.07 card-repeats:: 5 card-ease-factor:: 2.28 card-next-schedule:: 2023-01-02T21:21:34.885Z card-last-reviewed:: 2022-11-14T20:21:34.886Z card-last-score:: 3
    • The Operating System interfaces between a user's program and the hardware, provides a variety of services, and performs supervisory functions.
  • What is the purpose of the Hardware?
    • The Hardware performs the tasks.

• Seven Great Ideas in Computer Organisation

  • 1. Use Abstraction to Simplify Design #card

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    • A major productivity technique for hardware & software is to use abstractions to characterise the design at different levels of representation
    • Lower-level details are hidden to offer a simpler model at higher levels.

  • 2. Make the Common Case Fast #card

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    • Making the common case fast will tend to enhance performance better than optimising the rare case.
    • The common case is often simpler than the rare case, and hence is usually easier to enhance.

  • 3. Performance via Parallelism #card

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    • Involves speeding up performance by using designs that compute operations in parallel.

  • 4. Performance via Pipelining #card

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    • Performance via Pipelining is a particular pattern of parallelism that is so prevalent in computer architecture that it merits its own name.

  • 5. Performance via Prediction #card

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    • In some cases, it can be ^^faster on average to guess and start working^^ that to wait until you know for sure (assuming that the mechanism to recover from a misprediction is not too expensive, and your prediction is relatively accurate).

  • 6. Hierarchy of Memories #card

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    • Computer Architects have found that they can address conflicting demands with a hierarchy of memories.
      • The ^^fastest, smallest, & most expensive memory per bit^^ is at the top of the hierarchy.
      • The ^^slowest, largest, & cheapest per bit^^ is at the bottom of the hierarchy.

  • 7. Dependability via Redundancy #card

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    • Since any physical device can fail, we make systems dependable by including ^^redundant components^^ that can take over when a failure occurs and help detect failures.

• Hardware Organisation

  • What does basic computer organisation look like? #card card-last-interval:: 33.64 card-repeats:: 4 card-ease-factor:: 2.9 card-next-schedule:: 2022-11-22T23:24:24.522Z card-last-reviewed:: 2022-10-20T08:24:24.523Z card-last-score:: 5
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  • What is an integrated circuit? card-last-interval:: 31.36 card-repeats:: 4 card-ease-factor:: 2.8 card-next-schedule:: 2022-11-04T20:17:29.178Z card-last-reviewed:: 2022-10-04T12:17:29.178Z card-last-score:: 5 collapsed:: true
    • An integrated circuit, also called a chip, is a device combining dozens to millions of transistors.

  • The CPU

    • What is a CPU? #card card-last-interval:: 29.26 card-repeats:: 4 card-ease-factor:: 2.66 card-next-schedule:: 2022-12-13T22:47:19.225Z card-last-reviewed:: 2022-11-14T16:47:19.226Z card-last-score:: 5
      • The Central Processing Unit (CPU), also called the processor, is the ^^active part of the computer^^, which contains the datapath & control, and which adds numbers, tests numbers, signals I/O devices to activate, and so on.
      • The CPU is ^^responsible for executing programs.^^
    • What are the steps that the CPU takes to process programs? #card card-last-interval:: 64.01 card-repeats:: 5 card-ease-factor:: 2.52 card-next-schedule:: 2023-01-17T20:21:39.209Z card-last-reviewed:: 2022-11-14T20:21:39.209Z card-last-score:: 5
      • 1. Fetch: Retrieve an instruction from ^^program memory.^^
      • 2. Decode: Break down the instruction into parts that have significance to specific sections of the CPU.
      • 3. Execute: Various portions of the CPU are connected to perform the desired operation.
      • 4. Write Back: Simply "writes back" the results of the execute step ^^if necessary.^^

    • CPU Organisation

      • What does the organisation of the CPU look like? #card card-last-interval:: -1 card-repeats:: 1 card-ease-factor:: 1.94 card-next-schedule:: 2022-11-15T00:00:00.000Z card-last-reviewed:: 2022-11-14T20:12:31.318Z card-last-score:: 1
        • Processors are made up of:
          • A Control Unit
          • Execution Unit(s)
          • A Register File
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      • Control Unit

        • What does the Control Unit do? #card card-last-interval:: -1 card-repeats:: 1 card-ease-factor:: 2.56 card-next-schedule:: 2022-11-15T00:00:00.000Z card-last-reviewed:: 2022-11-14T16:48:27.996Z card-last-score:: 1
          • The Control Unit ^^controls the execution^^ of the instructions stored in main memory.
            • It ^^retrieves & executes^^ them.
        • What is the architecture of the control unit? #card card-last-interval:: -1 card-repeats:: 1 card-ease-factor:: 2.08 card-next-schedule:: 2022-11-15T00:00:00.000Z card-last-reviewed:: 2022-11-14T20:18:27.653Z card-last-score:: 1
          • The control unit contains a fetch unit, a decode unit, and an execute unit.
          • It also contains two special registers:
            • Program Counter (PC): keeps the address of the next instruction
            • Instruction Register (IR): keeps the instruction being executed
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  • The Memory Subsystem

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    • How is the memory divided into storage locations? #card card-last-interval:: 29.26 card-repeats:: 4 card-ease-factor:: 2.66 card-next-schedule:: 2022-12-13T22:41:41.185Z card-last-reviewed:: 2022-11-14T16:41:41.185Z card-last-score:: 5
      • Memory is divided into a set of storage location which can hold data.
        • Locations are numbered.
        • Addresses are used to tell the memory which location the processor wants to access.
    • What are the two hierarchies of memory? #card card-last-interval:: 10.97 card-repeats:: 3 card-ease-factor:: 2.56 card-next-schedule:: 2022-11-25T15:41:01.018Z card-last-reviewed:: 2022-11-14T16:41:01.018Z card-last-score:: 5
      • 1. Nonvolatile / ROM (Read Only Memory): Read only memory.
        • Used to store the BIOS and / or a bootstrap or bootloader program.
      • 2. Volatile / RAM (Random Access Memory): Read / Write memory.
        • Also called Primary Memory.
        • Used to hold the programs, operating system, and data required by the computer.

    • Primary Memory

      • How is primary memory connected to the CPU? #card card-last-interval:: 33.64 card-repeats:: 4 card-ease-factor:: 2.9 card-next-schedule:: 2022-12-15T02:38:12.876Z card-last-reviewed:: 2022-11-11T11:38:12.876Z card-last-score:: 5
        • Primary Memory is directly connected to the Central Processing Unit of the computer.
          • It must be present for the CPU to function correctly.
      • What are the three types of Primary Storage? #card card-last-interval:: -1 card-repeats:: 1 card-ease-factor:: 2.08 card-next-schedule:: 2022-11-15T00:00:00.000Z card-last-reviewed:: 2022-11-14T16:35:22.469Z card-last-score:: 1
        • 1. Processor Register:
          • Contains information that the CPU needs to carry out the current instruction.
        • 2. Cache Memory:
          • A special type of internal memory used by many CPUs to increase their throughput.
        • 3. Main Memory:
          • Contains the programs that are currently being run and the data that the programs are operating on.
    • What is the address width? #card card-last-interval:: 47.41 card-repeats:: 5 card-ease-factor:: 2.28 card-next-schedule:: 2023-01-07T22:09:51.569Z card-last-reviewed:: 2022-11-21T13:09:51.569Z card-last-score:: 3
      • The address width is the number of bits used to represent an address in memory.
      • The width limits the amount of memory that a computer can access.
        • Most computers use a 64 bit address, which means that the maximum number of locations is 2^{64} \approx 16 billion gigabytes.
    • What operations does the memory subsystem support? #card card-last-interval:: 28.3 card-repeats:: 4 card-ease-factor:: 2.66 card-next-schedule:: 2022-12-12T23:44:58.031Z card-last-reviewed:: 2022-11-14T16:44:58.031Z card-last-score:: 3
      • The memory subsystem supports two operations:
        • Load (or read) + the address of the data location to be read.
        • Store (or write) + the address of the location & the data to be written.
    • How many bytes may the memory system read or write at a time? #card card-last-interval:: 29.26 card-repeats:: 4 card-ease-factor:: 2.66 card-next-schedule:: 2022-12-13T22:41:30.763Z card-last-reviewed:: 2022-11-14T16:41:30.764Z card-last-score:: 5
      • Read & Write operations ^^operate at the width of the system's data bus^^, usually 32 bit or 64 bit.
    • How is a section of memory addressed? #card card-last-interval:: -1 card-repeats:: 1 card-ease-factor:: 2.8 card-next-schedule:: 2022-11-15T00:00:00.000Z card-last-reviewed:: 2022-11-14T16:43:58.787Z card-last-score:: 1
      • The address ^^contains only the address of the lowest byte^^, and a number of bytes to be read is specified, e.g., 4 bytes.

    • Memory Alignment & Words of Data

      • When the computer's word size is 4 bytes, the data to be read should be at a memory address which is ^^some multiple of four.^^
      • When this is not the case, e.g., the data starts at address 14 instead of 16, then the computer has to read two or more 4 byte chunks and do some calculation before the requested data has been read, or it may generate ^^an alignment fault.^^
      • Even though the previous data structure end is at, for example, address 13, the next data structure should start at address 16. Two padding bytes are inserted between the two data structures at addresses 14 & 15 to align the next data structure at address 16.

  • The I/O Subsystem

    • What are input devices? #card collapsed:: true card-last-interval:: 33.64 card-repeats:: 4 card-ease-factor:: 2.9 card-next-schedule:: 2022-12-18T07:38:20.415Z card-last-reviewed:: 2022-11-14T16:38:20.415Z card-last-score:: 5
      • Anything that feeds data into the computer.
    • What are output devices? #card collapsed:: true card-last-interval:: 33.64 card-repeats:: 4 card-ease-factor:: 2.9 card-next-schedule:: 2022-12-18T07:38:27.684Z card-last-reviewed:: 2022-11-14T16:38:27.684Z card-last-score:: 5
      • Display / transmit information back to the user.
    • What does the I/O Subsystem contain? #card collapsed:: true card-last-interval:: 33.64 card-repeats:: 4 card-ease-factor:: 2.9 card-next-schedule:: 2022-12-18T07:38:17.443Z card-last-reviewed:: 2022-11-14T16:38:17.443Z card-last-score:: 5
      • The I/O Subsystem contains the devices that the computer uses to communicate with the outside world and to store data.
    • How do I/O devices communicate with the processor? #card collapsed:: true card-last-interval:: 10.24 card-repeats:: 3 card-ease-factor:: 2.32 card-next-schedule:: 2022-11-24T21:49:01.266Z card-last-reviewed:: 2022-11-14T16:49:01.266Z card-last-score:: 3
      • I/O devices usually communicate with the processor using the I/O Bus.
        • PCs use the PCI Express (Peripheral Component Interconnect Express) bus for their I/O bus.
        • The Operating System needs a device driver to access a given I/O device.
          • What is a device driver? #card card-last-interval:: 33.64 card-repeats:: 4 card-ease-factor:: 2.9 card-next-schedule:: 2022-12-18T07:43:53.294Z card-last-reviewed:: 2022-11-14T16:43:53.295Z card-last-score:: 5
            • A device driver is a program that allows the OS to control an I/O device.

  • I/O Read / Write Operations

    • The I/O read & write operations are similar to the memory read & write operations.
    • How does the processor address I/O devices? #card card-last-interval:: 12.96 card-repeats:: 4 card-ease-factor:: 1.8 card-next-schedule:: 2022-11-27T19:18:57.241Z card-last-reviewed:: 2022-11-14T20:18:57.241Z card-last-score:: 3
      • A processor may use:
        • Memory-Mapped I/O: when the address of the I/O device is in the direct memory space, and the ^^sequences to read/write data in the device are the same as the memory read/write sequences.^^
        • Isolated I/O: similar process to Memory-Mapped I/O, but the processor has a ^^second set of control signals to distinguish between a memory access and am I/O access.^^
      • What is IO/M? #card card-last-interval:: 19.01 card-repeats:: 4 card-ease-factor:: 2.18 card-next-schedule:: 2022-12-03T20:02:23.177Z card-last-reviewed:: 2022-11-14T20:02:23.177Z card-last-score:: 3
        • IO/M is a status signal in Isolated I/O that denotes whether the read/write operation pertains to the memory or to the I/O subsystem.
          • When the signal is low (IO/M = 0), i.e., IO/M is true, it denotes memory-related operations.
          • When the signal is high, (IO/M = 1), i.e., IO/M is false, it denotes an I/O operation.

• Programs

  • What are programs? #card card-last-interval:: 23.43 card-repeats:: 4 card-ease-factor:: 2.42 card-next-schedule:: 2022-12-08T02:39:39.879Z card-last-reviewed:: 2022-11-14T16:39:39.879Z card-last-score:: 3
    • Programs are ^^sequences of instructions^^ that tell the computer what to do.
    • To the computer, a program is made out of a ^^sequence of numbers that represent individual operations.^^
      • These operations are known as machine instructions or just instructions.
      • A set of instructions that a processor can execute is known as an instruction set.

  • Program Development Tools

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    • What is a high-level programming language? #card card-last-interval:: 33.64 card-repeats:: 4 card-ease-factor:: 2.9 card-next-schedule:: 2022-12-18T07:43:16.217Z card-last-reviewed:: 2022-11-14T16:43:16.218Z card-last-score:: 5
      • A high-level programming language is a ^^portable language^^ such as C that is ^^composed of words & algebraic notation^^ that can be translated by a compiler into assembly language.
    • What is a compiler? #card card-last-interval:: 33.64 card-repeats:: 4 card-ease-factor:: 2.9 card-next-schedule:: 2022-12-18T07:38:38.718Z card-last-reviewed:: 2022-11-14T16:38:38.719Z card-last-score:: 5
      • A compiler is a program that translates statements in a given high-level language into assembly language statements.
    • What is an assembler? #card card-last-interval:: 33.64 card-repeats:: 4 card-ease-factor:: 2.9 card-next-schedule:: 2022-12-18T07:43:18.677Z card-last-reviewed:: 2022-11-14T16:43:18.677Z card-last-score:: 5
      • An assembler is a program that translates symbolic, assembly language versions of instructions into the ^^binary version.^^
    • What is Assembly Language? #card card-last-interval:: 108 card-repeats:: 5 card-ease-factor:: 3 card-next-schedule:: 2023-03-02T20:22:13.316Z card-last-reviewed:: 2022-11-14T20:22:13.317Z card-last-score:: 5
      • Assembly Language is a ^^symbolic representation^^ of machine instructions.
    • What is Machine Language? #card card-last-interval:: 19.01 card-repeats:: 4 card-ease-factor:: 2.18 card-next-schedule:: 2022-12-03T20:02:29.114Z card-last-reviewed:: 2022-11-14T20:02:29.114Z card-last-score:: 3
      • Machine Language is a ^^binary representation^^ of machine instructions.
    • What is an instruction? #card card-last-interval:: 28.3 card-repeats:: 4 card-ease-factor:: 2.66 card-next-schedule:: 2022-12-12T23:49:56.176Z card-last-reviewed:: 2022-11-14T16:49:56.176Z card-last-score:: 3
      • An instruction is a command that the computer hardware understands & obeys.

• Operating Systems

  • What is an Operating System? #card card-last-interval:: 9.68 card-repeats:: 3 card-ease-factor:: 2.42 card-next-schedule:: 2022-11-24T08:36:28.473Z card-last-reviewed:: 2022-11-14T16:36:28.474Z card-last-score:: 5
    • Possible definition: a program that runs on the computer that ^^knows about all the hardware^^ and usually ^^runs in privileged mode^^, having ^^access to physical resources that user programs can't control^^, and has the ^^ability to start & stop user programs.^^
    • The OS is responsible for managing the physical resources of complex systems, such as PCs, workstations, mainframe computers, etc.
    • It is also responsible for ^^loading & executing programs^^ and ^^interfacing with the users.^^
  • Usually, there is no operating system for small embedded systems.
    • Computers designed for one specific task.

  • Multiprogramming

    • What is Multiprogramming? #card card-last-interval:: 28.3 card-repeats:: 4 card-ease-factor:: 2.66 card-next-schedule:: 2022-11-17T15:33:42.952Z card-last-reviewed:: 2022-10-20T08:33:42.952Z card-last-score:: 5
      • Multiprogramming is a technique that allows the system to ^^present the illusion that multiple programs are running on the computer simultaneously.^^
    • Many multiprogrammed computers are multiuser.
      • They allow multiple users to be logged in at a time.
    • How is multiprogramming achieved? #card card-last-interval:: 28.3 card-repeats:: 4 card-ease-factor:: 2.66 card-next-schedule:: 2022-12-12T23:46:17.294Z card-last-reviewed:: 2022-11-14T16:46:17.294Z card-last-score:: 3
      • Multiprogramming is achieved by ^^switching rapidly between programs.^^
    • How does the processor decide which process to execute next? #card card-last-interval:: 23.43 card-repeats:: 4 card-ease-factor:: 2.42 card-next-schedule:: 2022-12-08T02:44:23.286Z card-last-reviewed:: 2022-11-14T16:44:23.287Z card-last-score:: 5
      • FCFS - First Come, First Served: processes are moved to the CPU in the order in which they arrive.
      • SJN - Shortest Job Next: looks at all processes in the ready state and dispatches the one with the smallest service time.
      • Round Robin: distributes the processing time equitably among all ready processes.

    • Context Switching

      • What is a Context Switch? #card card-last-interval:: 64.01 card-repeats:: 5 card-ease-factor:: 2.52 card-next-schedule:: 2023-01-24T13:09:58.962Z card-last-reviewed:: 2022-11-21T13:09:58.962Z card-last-score:: 5
        • When a program timeslice ends, the OS stops it, removes it, and gives another program control over the processor.
          • This is a context switch.
      • How does the OS go about a Context Switch? #card card-last-interval:: 15.05 card-repeats:: 4 card-ease-factor:: 1.94 card-next-schedule:: 2022-11-29T17:40:02.859Z card-last-reviewed:: 2022-11-14T16:40:02.859Z card-last-score:: 3
        • copies the current program register file into memory
        • restores the contents of the next program's register file into the processor
        • starts executing the next program
      • From the program point of view, ^^no program can tell that a context switch has been performed.^^

    • Protection

      • Three rules of Protection in multiprogrammed computers: #card card-last-interval:: 29.21 card-repeats:: 5 card-ease-factor:: 1.94 card-next-schedule:: 2022-12-17T00:35:54.999Z card-last-reviewed:: 2022-11-17T19:35:55.000Z card-last-score:: 3
        • 1. The result of any program running on the multiprogram computer ^^must be the same as if the program was the only program running on the computer.^^
        • 2. Programs ^^must not be able to access other programs' data^^ and must be confident that their data will not be modified by other programs (for security and privacy).
        • 3. Programs ^^must not interfere with other programs' use of I/O devices.^^
      • How is protection achieved? #card card-last-interval:: 15.05 card-repeats:: 4 card-ease-factor:: 1.94 card-next-schedule:: 2022-11-29T21:01:17.902Z card-last-reviewed:: 2022-11-14T20:01:17.902Z card-last-score:: 3
        • Protection is achieved by the ^^operating system having full control over the resources of the system (processor, memory, and I/O devices)^^ through:
          • Privileged Mode: the operating system is the only one that can control the physical resources it executes in privileged mode.
            • User programs execute in user mode.
          • Virtual Memory: each program operates as if it were the only program on the computer, occupying a full set of the address space in its virtual space.
            • The OS is translating memory addresses that the program references into physical addresses used by the memory system.
• Next Topic: Programming Models