Today

1
Todays Topics

• Introduction to computing
• Universal computational devices
• Levels of transformation

2
Our Approach to Computers

• GOAL construct the foundation, layer by layer,
  needed to learn to program in C
• A computer directs the processing of information
  (selects next task to be performed) and performs
  the processing
• We mean CPU, not peripherals that form a computer
  system

3
What We Will Study

• How information is encoded
• Transistors
• Von Neumann machine
• LC-2 (little computer)
• Machine language
• Assembly language

4
The Hardware

• Computers are a systematically interconnected
  collection of simple parts
• Deterministic system
• Parts are connected by wires, which can be at
  high or low voltage
• presence of voltage 1
• absence of voltage 0
• All information is encoded using 0s
  and 1s

5
Two Important Ideas

• All computers are capable of computing the same
  thing (given enough time and memory)
• A sequence of activities is necessary to
  translate solutions in English to activities
  carried out by electrons

6
Universal Computational Devices

• Universal means that anything that can be
  computed is possible to compute on the device (as
  opposed to specific)
• Alan Turing proposed a formal, mathematical
  definition of computation in 1937
• Turings Thesis every computation can be
  performed by some Turing Machine

7
Computing a Function
Simple Turing Machines ,
a b

Composing Functions
ab


?
c
8
Universal Turing Machines

• Universal Turing Machine can simulate any Turing
  Machine (takes an encoded machine description and
  its input)
• Since a UTM is programmable, it can compute
  anything a computer can compute!

9
Turings Other Contribution

• There are intractable problems that are very slow
  to solve, but they are solvable (but not
  feasible)
• Besides defining computation, Turing showed that
  there are functions that cannot be computed not
  by ANY computer EVER.
• e.g., The Halting Problem Solver it is
  impossible to write a program that will detect
  whether any other program will halt.

10
Levels of Transformation

• problems
• algorithms
• language
• ISA (machine architecture)
• microarchitecture
• circuits
• devices

11
Instruction Set Architecture

• ISA complete specification of the interface
  between programs and the hardware that carries
  out the work of the programs
• Set of instructions operations and operands
• Memory unique locations and their size
• C compiled to assembly language then assembled
  to ISA

12
Microarchitecture

• Microarchitecture implements the ISA (whats
  under the hood of the car.)
• e.g., DEC Alpha has 3 microarchitectures that
  vary in cost and performance

13
Circuits

• Each element of the microarchitecture is
  implemented out of simple logic circuits and
  there are cost/performance choices

14
Devices

• Each logic circuit is implemented in a particular
  device technology (e.g., CMOS, NMOS, gallium
  arsenide.)
• Electrons do the work at the device level wires
  carry electrons and to components that can detect
  and manipulate high and low voltage they do the
  work of storing and processing encoded values and
  instructions