Computer Architecture Overview

• In this course we will constantly be looking at computer architecture and organization.
  • Computer Architecture is a "description of the structure of a computer system made from component parts." (Wikipedia, 2024)
  • Computer Organization is the way in which the various components of a computer system are arranged to accomplish the architecture. (Part Wikipedia, part me)
• The Instruction Set Architecture or ISA is "the abstract interface between the hardware and the lowest level software that encompasses all of the information necessary to write a machine language program that will run correctly, including instructions, registers, memory access and so on." (Patterson and Hennessy, Hardware/Software Interface)
  • They actually define this as the computer architecture.
• For most of us, most of the time, computer architecture is all of this.
• As you might have guessed, this is tied closely to assembly language.
  • According to Jorgensen "assembly language is a "low-level" language and provides the basic instructional interface to the computer processor".
  • He incorrectly states that this is as close to the processor as you can get as a programmer.
  • You can actually get closer with machine language.
• As you might guess from the title of this class, we will be studying
  • The basics of computer architecture
  • The basics of assembly language
• But aren't all computers the same?
  • No not really.
  • If you look at history of architecture/implementation you will find a wide variety of designs and implementations.
  • We will generalize, but you can almost always find something that breaks the generalization.
  • Remember, this is engineering, not science.
  • Engineering "the practice of using natural science, mathematics and the engineering design process to solve technical problems, increase efficiency and productivity and improve systems." (Wikipedia)
• We will focus on computers constructed from transistors
  • For now, transistors are electronic switches.
  • Later we will examine these in more detail.
  • We will not consider quantum computers.
• Transistors can be combined to form logical gates
  • These gates can perform logical or boolean operations.
  • Typical gates include and, or, not
  • We will examine gates more closely later as well.
• Gates are combined to form circuits
  • Some well know circuits include adders, registers, multiplexers, ...
  • We will examine some of these circuits more closely later.
• These circuits are then combined to build computers.
• The main components of a computer are:
  • The CPU or central processing unit.
  • Primary storage or RAM (random access memory)
  • Secondary storage or
    • Hard drive
    • USB Drive
    • ...
    • (From Jorgensen)
  • I/O (input output) devices.
  • All of these are connected by one or more busses (or data transfer system)
• Back to are they all the same?
  • Most machines are built according to the von Neumann architecture.
    • Based on a paper by John von Neumann who worked on a draft report about the EDVAC (Electronic Discrete Variable Automatic Computer) computer system
      • A predecessor to ENIAC
      • At the University of Pennsylvania
    • von Neumann architecture describes a stored program computer
    • This is mostly what we call a computer today.
    • von Neumann said that memory holds both program and data.
    • An alternative, the Harvard Architecture says that you have different memory for program and data.
    • This difference will not matter to us.
  • However there are other machines in production today.
    • Parallel architectures come in several flavors.
    • Flynn's Taxonomy

      	Data
      Instruction	Single/Single SISD	Single/Multiple SIMD
      	Multiple/Single MISD	Multiple/Multiple MIMD

    • SISD is what you think you use
    • MIMD is probably what you use
      • Multiprocessor (multi core) are one type.
    • Your graphics card is probably SIMD
    • MISD computers are somewhat rare.
      • Mostly pipeline computers.
• Another difference can be the instruction set
  • Until the 70's instruction sets were designed with the programmer in mind.
    • There were many instructions to do very complex operations.
    • This was called CISC: Complex Instruction Set Computer
    • The current intel family is an example of a CISC
    • These machines became increasingly more expensive to
      • design
      • make run faster
  • Studying programs it was found
    • Most programs didn't use the entire instruction set.
      • There were many instructions that were never or rarely used.
    • Only expert assembly programmers could optimize better than a compiler
      • And compilers have continued to improve
    • So the RISC or reduced instruction set computer was designed.
    • The ARM chip is RISC, but so is the intel chip.
• Moore's Law
  • Observation that the number of transistors in an integrated circuit will double every two years.
  • Gordon Moore, was a major player in the IC industry
  • This observation occurred in 1965
  • The prediction has mostly held.
  • Many have declared it dead over the years.
  • But some say it's not dead yet!
  • (Max Roser, Hannan Ritchie)
• The Power Wall
  • This is from Hennessy and Patterson
  • As you increase speed, you increase the heat produced
  • And eventually you can not run a processor any faster.