The Analytical EngineModule 6

Program Translation

The Binary Machine

Computers store their programs and information in binary code.

A program must be understandable to both the user and the machine.

The Binary Machine

Translation from high-level language (English) to low-level language (binary) is accomplished through a program:– Compiler– Interpreter– Assembler

High-level Low-level Source code Object code

The Binary Machine

All computers have a hard-wired instruction set that is unique to a specific microprocessor.

Therefore, compilers, interpreters, and assemblers must be written for a specific machine.

The Binary Machine

An instruction is a unique set of binary patterns that cause the circuitry of the machine to behave in a certain way.

These circuits are etched into the microprocessor chip.

Binary Representations

Binary architecture– Bit – Binary Digit– Nibble(?) – 4 bits– Byte – 8 bits– Word – 2 bytes – 16 bits (at least)

Binary Representations

Most modern desktop PCs and Macs measure their memory size in bytes.– 1 MB = 1 million bytes– 12 MB = 12 million bytes or 96 million bits!– 1 GB = 1 gigabyte or 1 billion bytes.

Binary Representations

To a computer, binary digits can represent:– Simple binary code

Integers - 0000 0000 0000 0010 = 2 Integers – 0111 1111 1111 1111 = 32767 Real Numbers (32 bits) – sign(1 bit), Exponent (8) bits,

Mantissa (23 bits)

Binary Representations

To a computer, binary digits can represent:– Binary Coded Decimal Numbers (BCD)

0000 0011 0001 0110 = 316

– Hexadecimal Numbers (Hex) 1111 0101 0011 1011 = F53B

Binary Representations

To a computer, binary digits can represent:– ASCII Code

0100 0001 = “A” 0010 0001 = “!”

– Check ASCII table handout.– Adopted so computers could represent character

(non-numeric) data.

Binary Representations

Instruction Codes– Arbitrary – Ex. Is PIPPIN

0001 0100 = LOD (Load accumulator) 0000 0101 = STO (Store accumulator contents)

– A 256-instruction set can be encoded in 8 bits.– Trend was to richer instruction sets.– Trend now to reduced instruction sets.

The Binary Machine

Observe the demonstration of the PIPPEN machine carefully.

A Simple Computer

RAM – Random Access Memory– Data – 8, 16, 32 bits– Instructions

8-bit instruction code 8-bit address

PC – Program Counter– Keeps address of current instruction

A Simple Computer

Accumulator– Special memory location that stores intermediate

results of computations. IR – Instruction Register

– Holds a copy of the current instruction to be executed.

Decoder– takes a single input and transfers to multiple

outputs.

A Simple Computer

MUX – Multiplexor– Routes multiple inputs to a single output.

ALU – Arithmetic Logic Unit– Performs mathematical operations on its input.

A Simple Computer

Assembler – translates mne-monic represen-tations of instructions into binary code.

(LOD, ADD, SUB, STO, etc.)

Very fast Programmer is

responsible for data storage

One instruction – One operation correspondance

Language Implementation

Scanning – breaking a string of characters into meaningful pieces called tokens.– W = X – Y ;

Like breaking down a sentence into words.

Language Implementation

Parsing – Arranging tokens into a sensible logical structure.

– W = X + Y * Z; E1 = Y * Z E2 = X + E1 E2 W

– Result is called a Parse Tree.

Code Generation – generating one or more machine language instructions based on the Parse Tree.

Language Types

Interpreted Languages– BASIC, LISP, JavaScript

Program LineInterpreterBinary CodeExecution Next LineInterpreterBinary CodeExecution

– Fairly slow Lines translated repeatedly One line may generate multiple instructions, some unnecessary

– User does not need to know details of the machine. Programs run on any machine that has the interpreter.

Language Types

Compiled Languages– COBOL, FORTRAN, C, C++, Java

Entire programCompilerBinary CodeExecution

– Fairly fast after compilation Better error detection. Object program can be stored and run repeatedly without

recompilation.

– User does not need to know details of the machine. Programs run on any machine that has a compiler.

Language Groups

Imperative – fundamental unit is the procedure which is called by a main program.– Pascal, FORTRAN, Ada

Functional – processes are defined in terms of functions with no main program.– LISP

Language Groups

Declarative – Input/Output oriented; limited procedure/function support.– COBOL, Prolog

Object-Oriented – processes controlled by “events” which communicate with “objects” via “messages”.– C++, Smalltalk, JavaScript, Java

Language Design

Syntax & Semantics Data Types

– Strongly Typed– Weakly Typed

Data Structures– Arrays– Lists

Decision statements– IF– IF – ELSE

Control Statements– FOR– WHILE– WHILE – DO

Language Implementation

Generating Code Observe the demon-

stration carefully. Check the course web

page and then complete Lab 6.3.

Language Generations

First Generation – machine language Second Generation – assemblers Third Generation – interpreted and compiled

languages. Fourth Generation – object-oriented

languages

Language Implementation

Symbols & Bits Observe the demon-

stration carefully. Check the course web

page for special instructions.

Complete Lab 6.4.

The End

Program Translation