Introduction to Computer Organization
CEG 320/520: Computer Organization and Assembly Language Programming
Computer Organization Intro 1
Computer Organization: Goals
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Instruction cycle (fetch, execute, store)
Memory organization
– Big endian / little endian
– Bytes, words, long
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Primary components of a computer
– CPU (control unit, ALU, registers), memory, I/O, datapath
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Von Neumann Architecture
– Stored program computer
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Know about ISAs. What are they? How do they fit in?
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Assigned Reading
– General Computer Organization: HVZ Chapter 1, 7.1, 7.2
– Memory: HVZ Chapter 2.2
CEG 320/520: Computer Organization and Assembly Language Programming
Computer Organization Intro 2
What is a computer?
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What is computation?
There are many sorts of computing devices, they fall into two categories:
– Analog: machines that produce an answer that measures some continuous
physical property such as distance, light intensity, or voltage. Examples?
– Digital: machines that perform computations by manipulating a fixed finite
set of elements. Examples?
– The difficulty with analog devices is that it is very hard to increase their
accuracy.
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Before modern digital computers, the most common digital machines
were adding machines.
– Adding machines perform exactly one sort of operation.
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Computers also perform one operation… but their operation is to accept
a set of instructions that tell it how to do any sort of computation.
CEG 320/520: Computer Organization and Assembly Language Programming
Computer Organization Intro 3
Universal computing devices
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Turing’s Thesis: Computer scientists believe that ANYTHING that can be
computed, can be computed by a computer (provided that it has enough time
and enough memory).
What does this imply?
– All computers (from the least expensive to the most expensive) are capable of
computing EXACTLY the same things IF they are given enough time and enough
memory.
– Some computers can do things faster, but none can do more than any other
computer.
– All computers can do exactly the same things!
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Thus, any given problem is either computable or it is not computable
– Problems may be computable, but still not feasible (NPC)
CEG 320/520: Computer Organization and Assembly Language Programming
Computer Organization Intro 4
How do we get the electrons to do the work?
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We describe our problems in English or some other natural language.
Computer problems are solved by electrons flowing around inside the
computer.
It is necessary to transform our problem from a natural language to the
voltages that influence the flow of electrons.
This transformation is really a sequence of systematic transformations,
developed and improved over the last 50 years, which combine to give the
computer the ability to carry out what may appear to be very complicated
tasks. In reality, these tasks must be simple and straight-forward.
CEG 320/520: Computer Organization and Assembly Language Programming
Computer Organization Intro 5
Overview: Digital Computation
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Design Process
The Problem
Software level
Computer Science
Algorithm & Language
Hardware level
Computer Engineering
ISA & Microarchitecture
Logic level
Computer/Electrical Engineering
Circuits & Devices
CEG 320/520: Computer Organization and Assembly Language Programming
Computer Organization Intro 6
Overview: The Problem Statement
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The Problem
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Algorithm & Language
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We describe problems that we wish to solve with a
computer in a “natural language.”
Natural languages are fraught with a lot of things
unacceptable for providing instructions to a computer.
The most important of these unacceptable attributes is
ambiguity. To infer the meaning of a sentence, a listener
is often helped by context that the computer does not
have.
Example: “Time flies like an arrow.”
– How fast time passes
– Track meet
– Gossip
ISA & Microarchitecture
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A computer is an electronic idiot and can not deal with
any ambiguity, thus…
Circuits & Devices
CEG 320/520: Computer Organization and Assembly Language Programming
Computer Organization Intro 7
Overview: Algorithm
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The Problem
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The first step in the sequence of transformations is to
transform the natural language description of the
problem to an algorithm.
An algorithm is a step-by-step procedure:
– That transforms an input (possibly NULL) into some
output (or output action)
– That is guaranteed to terminate
Algorithm & Language
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ISA & Microarchitecture
Definiteness: Each step is precisely stated.
Effective computability: Each step must be something the
computer can perform
Finiteness: The procedure must terminate
For any computable problem, there are an infinite
number of algorithms to solve it.
– Which solution is best?
Circuits & Devices
CEG 320/520: Computer Organization and Assembly Language Programming
Computer Organization Intro 8
Overview: Programming Language
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The Problem
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Algorithm & Language
The next step is to transform the algorithm into a
computer program
Programming languages are unambiguous
“mechanical” languages
There are two kinds of programming languages:
– High-level languages are machine independent.
They are “far above” the (underlying) computer
– Low-level languages are machine dependent. They
are tied to the computer on which the program will
execute. There is generally only one such language
per machine (referred to as its ASSEMBLY
language).
ISA & Microarchitecture
Circuits & Devices
CEG 320/520: Computer Organization and Assembly Language Programming
Computer Organization Intro 9
Overview: The instruction set architecture (ISA)
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The Problem
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– Examples: IA-32 (Intel, AMD, and others), PowerPC
(Motorola)
Algorithm & Language
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ISA & Microarchitecture
The next step is to translate the program into the
instruction set of the particular computer that will be
used to carry out the work of the program.
The Instruction Set Architecture (ISA) is the complete
specification of the interface between programs that have
been written and the underlying hardware that must carry
out the work of those programs.
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Programs are translated from high languages in to the
ISA of the computer on which they will be run by a
program called a compiler (specific to the ISA).
Programs are translated from assembly to the ISA by an
assembler
Analogy: A car
– The car’s ISA describes what the driver sees/uses.
Circuits & Devices
CEG 320/520: Computer Organization and Assembly Language Programming
Computer Organization Intro 10
Overview: Microarchitecture
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The Problem
– The IA-32 has been implemented by several
different processors over the past twenty years 8086
(Intel, 1979), 8286, 8386, 8486, Pentium, PentiumII,
Athlon, PentiumIII.
– Each implementation is an opportunity for computer
designers to make different trade-offs between cost
and performance. [Computer design is always an
exercise in trade-offs.]
Algorithm & Language
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ISA & Microarchitecture
Circuits & Devices
The next step is to transform the ISA into an
implementation. The detailed organization of an
implementation is called its microarchitecture.
Analogy: A car
– The implementation of a car’s ISA is what goes on
under the hood. Here all automobiles makes and
models are different. Some with fuel injection, some
have eight cylinders, some are turbocharged… in
each case the “microarchitecture” of a specific
automobile is the result of the automobile designers’
decisions regarding cost and performance.
CEG 320/520: Computer Organization and Assembly Language Programming
Computer Organization Intro 11
Overview: Logic Circuits
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The Problem
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Algorithm & Language
The next step is to implement each element of the
microprocessor out of simple logic circuits.
Here there are also choices, as the logic designer
decides how to best make the trade-offs between
cost and performance.
Even in the case of addition, there are several
choices of logic circuits to perform this operation
and differing speeds and corresponding costs.
ISA & Microarchitecture
Circuits & Devices
CEG 320/520: Computer Organization and Assembly Language Programming
Computer Organization Intro 12
Overview: Digital Devices
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The Problem
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Finally, each basic logic circuit is implemented in
accordance with the requirements of the particular
device technology used.
So, CMOS circuits are different from NMOS
circuits, which are different, in turn, from gallium
arsenide circuits.
Algorithm & Language
Vcc
Rc
ISA & Microarchitecture
Vin
Vout
Rb
Circuits & Devices
CEG 320/520: Computer Organization and Assembly Language Programming
GND
Computer Organization Intro 13
Logic Circuits: Types
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Logic circuits divide into two major types:
– Combinational Logic
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Current output depends on current input only
Examples: gates, decoders, multiplexors (MUXs), ALUs
– Sequential Logic
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m
n
p
Current output depends on past inputs as well as current input
Thus has a memory (usually called the state)
Examples: latches, flip-flops, state machines, counters, shift registers
+
*
p * (m + n)
CEG 320/520: Computer Organization and Assembly Language Programming
Design:
avg (w,x,y,z)
a^2+2ab+b^2
Computer Organization Intro 14
Logic Circuits: Sequential
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STATE- A collection of state variables whose values at any one time contain
all the information about the past values necessary to account for future
behavior.
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Example: A TV tuner could have a current channel stored internally, so the
next channel can be predicted as a function of the inputs, i.e. the UP button
increases the channel by one, the DOWN button decreases the channel by
one. What is the state of this TV tuner?
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Digital sequential logic
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–
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State variables are binary values
Circuit with n binary state variables has 2n possible states
Also known as a finite state machine (FSM).
Changes usually synchronized with a system clock
CEG 320/520: Computer Organization and Assembly Language Programming
Computer Organization Intro 15
The instruction set
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High-Level Language - C
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A = B + C;
– Memory-Transfer Equivalent
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Mem[A]  Mem[B] + Mem[C]
Mem[EA00]  Mem[EA08] + Mem[EA10]
Machine-Level Equivalent
– Assembly (human readable)
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Load R2, B
Load R3, C
R2  R2 + R3
Store A, R2
ex: Machine (for a simple architecture)
E2EA08
E3EA10
0223
F2EA00
The bits of a machine instruction are divided into fields
– eg: E2EA08
– E: Operation “Load”; 2: Destination Address R2; EA08: Address Field
– The operation field (opcode) defines the format for the instruction
CEG 320/520: Computer Organization and Assembly Language Programming
Computer Organization Intro 16
How do we specify the program?
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Contemporary languages
– C, C++, Perl, Java, and hundreds more.
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Languages of Yore
– Fortran, COBOL, and scores more.
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Specialty languages
– VHDL, simulation languages, and thousands more.
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There are over 1,000 “standardized” programming languages today.
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The only goal of these languages is to help humans implement their
algorithms in the instructions available for a particular ISA
CEG 320/520: Computer Organization and Assembly Language Programming
Computer Organization Intro 17
Computer Organization: You should know…
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Instruction cycle (fetch, execute, store)
Memory organization
– Big endian / little endian
– Bytes, words, long

Primary components of a computer
– CPU (control unit, ALU, registers), memory, I/O, datapath

Von Neumann Architecture
– Stored program computer

Know about ISAs. What are they? How do they fit in?

Next Topic
– Introduction to Assembly Language
– Reading: HVZ Chapter 2.4, 2.5, 2.6, 3.8, 3.9, 3.10, 3.11
– Reference: HVZ Appendix C
CEG 320/520: Computer Organization and Assembly Language Programming
Computer Organization Intro 18