! Ancient computers. ! Today's microprocessors. Memory. ! Stores data and programs. ! 256 "words." (16 bits each) ! Special word for stdin / stdout.

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1 What is TOY?. The TOY Machine An imaginary machine similar to:! Ancient computers.! Today's microprocessors. Introduction to Computer Science Sedgewick and Wayne Copyright Why Study TOY? Inside the Box Machine language programming.! How do Java programs relate to computer?! Key to understanding Java references.! Still situations today where it is really necessary. multimedia, computer games, scientific computing, MMX, Altivec Computer architecture.! How is a computer put together?! How does it work? TOY machine. Optimized for simplicity, not cost or performance. Switches. Input data and programs. Lights. View data. Memory.! Stores data and programs.! "words." ( bits each)! Special word for stdin / stdout. Program counter (PC).! An extra -bit register.! Keeps track of next instruction to be executed..! Fastest form of storage.! Scratch space during computation.! registers. ( bits each)! Register is always. Arithmetic-logic unit (ALU). Manipulate data stored in registers. Standard input, standard output. Interact with outside world.

2 Data and Programs Are Encoded in ary ary Encoding Each bit consists of two states: How to represent integers?! or.! True or false.! Switch is on or off.! High voltage or low voltage.! Use binary encoding.! Ex: = Everything stored in a computer is a sequence of bits.! Data.! Programs.! Text, documents, pictures, sounds, movies, executables,? = = Hexadecimal Encoding Machine "Core" Dump How to represent integers? Machine contents at a particular place and time.! Use hexadecimal encoding.! ary code, four bits at a time. Hex Hex! Record of what program has done.! Completely determines what machine will do.! Ex: = = E A B C Main Memory D R R R R : E :? E F R R R R RD R RE R RF index of next instruction data program : : : :.. E: A B CAB C =! = +! + +! + + +! + + variables F: F:

3 A Sample Program A Sample Program A sample program. Adds + = D. TOY memory (program and data) comments Program counter. The is initially, so the machine interprets A as an instruction. : : : : : : : A " mem[] : B " mem[] : CAB " + : C mem[] " : halt index of next instruction to execute : A " mem[] : B " mem[] : CAB " + : C mem[] " : halt Remark. Since the is, machine interprets A as an instruction. Load Load Load. [oode ]! Loads the contents of some memory location into a register.! A means load the contents of memory cell into register A. Load. [oode ]! Loads the contents of some memory location into a register.! B means load the contents of memory cell into register B. : : : : : : : A " mem[] : B " mem[] : CAB " + : C mem[] " : halt : A " mem[] : B " mem[] : CAB " + : C mem[] " : halt?? A oode dest d addr B oode dest d addr

4 Add Store Add. [oode ]! Add contents of two registers and store sum in a third.! CAB means add the contents of registers A and B and put the result into register C. Store. [oode ]! Stores the contents of some register into a memory cell.! C means store the contents of register C into memory cell. : : : : : : : A " mem[] : B " mem[] : CAB " + : C mem[] " : halt D : A " mem[] : B " mem[] : CAB " + : C mem[] " : halt?? C A B oode dest d source s source t C oode dest d addr Halt Program and Data Instructions Halt. [oode ] Program: Sequence of instructions. : halt! Stop the machine. : add instruction types. : subtract! -bit word (interpreted one way). : and D : : : D D : A " mem[] : B " mem[] : CAB " + : C mem[] " : halt! Changes contents of registers, memory, and PC in specified, well-defined ways. Data. -bit word (interpreted other way). Program counter (). Stores memory address of the "next instruction." : xor : shift left : shift right : load address : load : store A: load indirect B: store indirect C: branch zero D: branch positive E: jump register F: jump and link

5 TOY Instruction Set Architecture Interfacing with the TOY Machine TOY instruction set architecture (ISA).! Interface that specifies behavior of machine.! register, words of main memory, -bit words.! instructions. To enter a program or data:! Set memory address switches.! Set data switches.! Press Load: data written into addressed word of memory. Each instruction consists of bits.! Bits - encode one of instruction types or oodes.! Bits - encode destination register d. To view the results of a program:! Set memory address switches.! Press Look: contents of addressed word appears in lights.! Bits - encode: [Format ] source registers s and t [Format ] -bit memory address or constant? Format oode dest d source s source t Format oode dest d addr Using the TOY Machine: Run Flow Control To run the program:! Set memory address switches to address of first instruction.! Press Look to set to first instruction.! Press Run button to repeat fetch-execute cycle until halt oode. Flow control.! To harness the power of TOY, need loops and conditionals.! Manipulate to control program flow. Fetch-execute cycle.! Fetch: get instruction from memory.! Execute: update move data to or from memory and registers, perform calculations. Fetch Execute Branch if zero. [oode C]! Changes depending on whether value of some register is zero.! Used to implement: for, while, if-else. Branch if positive. [oode D]! Changes depending on whether value of some register is positive.! Used to implement: for, while, if-else.

6 An Example: Multiplication Multiply Multiply. Given integers a and b, compute c = a! b. TOY multiplication. No direct support in TOY hardware. A: B: C: inputs output Brute-force multiplication algorithm:! Initialize c to.! Add b to c, a times. int a = ; int b = ; int c = ; while (a!= ) { c = c + b; a = a - ; } brute force multiply in Java loop D: E: constants : AA " mem[a] a : BB " mem[b] b : CD " mem[d] c = : E R " mem[e] always : CA if ( == ) " while (a!= ) { : CCB " + c = c + b : AA " - R a = a - : C " } Issues ignored. Slow, overflow, negative numbers. : CC mem[c] " : halt multiply.toy Step-By-Step Trace A Little History R : AA " mem[a] : BB " mem[b] : CD " mem[d] : E R " mem[e] : CA if ( == ) " : CCB " + : AA " R : C " : CA if ( == ) " : CCB " + : AA " R : C " : CA if ( == ) " : CCB " + B : AA " R : C " : CA if ( == ) " : CC mem[c] " : halt multiply.toy Electronic Numerical Integrator and Calculator (ENIAC).! First widely known general purpose electronic computer.! Conditional jumps, programmable.! Programming: change switches and cable connections.! Data: enter numbers using punch cards. John Mauchly (left) and J. Presper Eckert (right) ENIAC, Ester Gerston (left), Gloria Gordon (right) US Army photo: tons x x. ft, vacuum tubes multiply/sec

7 Basic Characteristics of TOY Machine Harvard vs. Princeton TOY is a general-purpose computer.! Sufficient power to perform ANY computation.! Limited only by amount of memory and time. Stored-program computer. [von Neumann memo, ]! Data and program encoded in binary.! Data and program stored in SAME memory.! Can change program without rewiring. Outgrowth of Alan Turing's work. (stay tuned) John von Neumann Harvard architecture.! Separate program and data memories.! Can't load game from disk (data) and execute (program).! Used in some microcontrollers. Von Neumann architecture.! Program and data stored in same memory.! Used in almost all computers. All modern computers are general-purpose computers and have same (von Neumann) architecture. Maurice Wilkes (left) EDSAC (right) Q. What's the difference between Harvard and Princeton? A. At Princeton, data and programs are the same.