Computer Architecture and Software

#Computer-Science#CS250#Computer-Architecture#Software

Computer §

• A computer is a machine that can be programmed to carry out a computation automatically

Architecture §

• Conceiving, planning, and designing structures

Therefore, Computer Architecture is… §

• Computer architecture (CA) is about conceiving, planning, and designing programmable structures that compute

Software §

• Software is a description of a computation, expressed in a programming language with any necessary data
  • Software and data are examples of information
• Most software is written in a high level language and syntax
• There are 2 main purposes of software
  • 1. Software is a way to define an algorithm and its data structures
  • 2. The value of software comes from its suitability to execute (run)
• Interpreters run software

Interpreters §

• Interpreters execute instructions expressed in a programming language
• Examples
  • Siri is an interpreter, she interprets human language and executes commands based on it
  • Python3 is an interpreter for Python, it executes Python commands
  • You yourself are an interpreter. For example, in the game of Simon Says you interpret the instructions and execute the proper response
• How are interpreters implemented?
  • They can be done in other software, for example Python3 is just a program
  • How do you execute Python3 though if its just more software?
    • You execute it with another interpreter! But what if that also needs interpreted? It just keeps going forever…
  • Eventually the interpreted code will reach the final interpreter, the computer/machine itself. At that point the computer/machine can directly interpret the instructions/software it is given
    • Basically, the software gets interpreted down to machine code, where the computer actually knows what to do

The Base Case Interpreter - The Computer §

• The base case interpreter is the lowest level. After the high level code has been interpreted and compiled and decompiled and whatever all the way down to machine code, 1’s and 0’s for the computer itself to read.
• These interpreters all have the capability to
  • Accept input
  • Store values
  • Update/change values
  • Compute things
  • Create output

Types of Computers §

Mechanical computers §

• Use mechanical parts to represent data and carry out operations of a computation
• Part shapes, sizes, and connections embody the data and computational operations
• Disadvantages
  • Parts are not small
  • Manufacturing parts individually is expensive
  • Parts require assembly which takes more expense
  • Parts degrade with use
  • Max speed is subsonic, so algorithms requiring many steps are slow
• Computers today still use moving parts, just not mechanical ones.

Electrons §

• We use ELECTRONS!
  • Electrons are miniscule mass, and they move fast
  • They have positive/negative charges
  • They have negligible volume
  • The computers can be fast, lightweight, and small. But, they might be expensive

Electronic Computers §

• Colossus - 1st programmable electronic computer
  • Used vacuum tubes
  • Designed and built in 1943 by British cartographers to break German cyphers
  • Vacuum tubes
    • Pros - Much faster
    • Cons - same volume as mechanical design
    • Con - Lots of energy needed
    • Con - they can burnout and fail needing to be swapped out
• AT&T started research in physics of electron behavior in Germanium crystals as a replacement for vacuum tubes
• 1st transistor designed and built by Bell Labs, made at Purdue with a Germanium crystal
• We have made $1.3\times 10^{22}$ transistors as of 2018
  • They are the most manufactured device ever
• Electronic computers today use silicon
  • Potential future materials are
    • Germanium Alloys
    • Graphene (from Carbon)

Archean §

• Archean Eon is about 33% of Earth’s history
• Only 22% of exposed continental crust
• Rocks are difficult to interpret
  • Commonly metamorphosed and deformed
  • Most rocks have been buried deeply
  • Few contain any clear fossils, since life was microscopic with no hard parts
• 
• Archean rocks in North America
  • Acasta Gneiss
  • Oldest known exposed rocks on Earth about 4 billion years old
  • Northwest Territories, Canada
  • Only meteorites and a few single zircon grains are older
  • Most Archean rocks in North America are underneath newer rocks
  • Some uplifted and exposed by later mountain building events
• Greenstone Belts
  • greenstone belts and granite-gneiss-complexes are most common Archean rocks
  • Belts > 2.8 billion years old are basaltic over ultramafic
  • Younger belts are more intermediate, andesite-rhyolite over basaltic
  • Upper sedimentary unit
  • Synclinal structures
• North American Greenstone Belts
  • Canadian Shield
    • Superior and Slave cratons
    • 2.7-2.5 billion years ago
  • Low-grade metamorphism
    • Often intruded by granitic magmas
    • Faulted
  • Sedimentary rocks
    • Sandstones and conglomerates
    • Mudstones
    • Carbonates
  • Banded iron formations
    • Fluctuating atmospheric oxygen levels
    • More common in Proterozoic
• Archean Plate Tectonics and the origin of cratons
  • Some kind of plate tectonics probably occurred during the Archean
  • Small cratons were present
    • Grew by accretion, lateral growth by island arc collision
    • Also, underplating with rising magmas accumulating below or within continental crust
  • By end of Archean (2.5 billion years ago)
    • 30-40% of the present volume of continental curst formed
  • Plates moved faster than today, more heat in Earth caused faster magma convection
• The atmosphere and hydrosphere
  • Early atmosphere quite different than modern
    • Hydrogen and helium, solar winds
  • Formation of core allowed atmospheric gases to accumulate
    • Magnetic field shielded atmosphere from solar wind
  • Outgassing from volcanic eruptions
    • Gases from Earth’s interior into the atmosphere
      • Water, Carbon dioxide, hydrogen, nitrogen
      • Methane and ammonia from chemical reactions
    • Very little free Oxygen in “oases”
  • Faint Young Sun paradox
    • The sun was only 70% as bright as today early in Earth’s history
      • Less energy to warm the Earth
    • All else equal, Earth should have been glaciated globally for the first half of its history
    • Evidence for liquid water
    • Requires larger greenhouse effect
  • Origin of the hydrosphere
    • Sources of surface water include
      • Outgassing from earths interior
      • Bombardment by meteorites and icy comets
      • Not known which is more important
    • Archean oceans existed
      • Evidence in sedimentary rocks and pillow basalts
      • Likely deeper than today
      • possibly saltier than today
• Archean Origin of life
  • Oldest fossils
    • 3.5 billion years ago for the oldest “biologic” fossils in Australia
  • Chemical evidence indicates photosynthesis existed at 3.8 billion years ago
  • Controversial isotopic evidence from zircons may suggest life by 4.1 billion years ago (Hadean)
  • 3.7 billion years ago “stromatolites” in Greenland