What you need to know about the stored program model

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1 What you need to know about the stored program model CMSC 122 CMSC 122 What you need to know about the stored program model 1 / 8

2 Outline 1 Introduction Overview of the Stored Program Model Using JavaScript to manipulate locations CMSC 122 What you need to know about the stored program model 2 / 8

3 Overview of the Stored Program Model What is the stored program model? Informally, a mathematical model offered by John von Neumann as a description of a machine capable of storing and performing algorithms or computer programs. Refresh your understanding: what is a an algorithm/program? A finite sequence of instructions; Well-defined criteria for success; Expressible (explainable) to the computer meaning that the problem can be represented in some formal language. Solution must be obtainable in an acceptable amount of time and space. Computer programs are machine-executable interpretations of algorithms. CMSC 122 What you need to know about the stored program model 3 / 8

4 Overview of the Stored Program Model How do we express programs and related elements? Some language that must be translatable into a language that the machine understands. But, what does work or the solution look like? Informally, the program transforms the data into something that looks like a solution. But where does this transformation take place? Where does data live? CMSC 122 What you need to know about the stored program model 4 / 8

5 Overview of the Stored Program Model Data & Program share memory Data and Program reside in memory This sounds like a simple statement, but it changed everything.... For one thing, this meant that data and program were composed of the same elements, i.e., bits. So we needed a way to tell these apart: location! Interpret the data starting at this location to mean this..., and.... Thus, the meaning of any element (object) in storage is its location, i.e., its address! But, because programs can write (transform) data and programs are data, programs can write programs. (More on this later!) CMSC 122 What you need to know about the stored program model 5 / 8

6 Using JavaScript to manipulate locations How does this look in JavaScript? Below are some typical JavaScript variable (and constant) declarations. /* reserve a space for avariablename */ var avariablename; /* reserve a space for avariablename and * store value in that space. */ var avariablename = value; // assigns value to avariablename /* reserve space for a constant named aconstantname * and set it to a value (that remains unchangable). */ const aconstantname = value; // assigns value to aconstantname CMSC 122 What you need to know about the stored program model 6 / 8

7 Using JavaScript to manipulate locations Some fine points here... The biggest conceptual problem novices have with many programming language is their use of the equals sign, =. Variables (and constants) name locations, which are places in the memory where values can be stored and retrieved. But, the equals sign, =, commonly names a binary relation between two objects that has certain properties (name these). In JavaScript it is called an assignment and it means the result of storing a value into a location. In pseudo-code, I write to mean avariablename = value; avariablename value CMSC 122 What you need to know about the stored program model 7 / 8

8 Using JavaScript to manipulate locations Pseudo-Code I will often use pseudo-code to describe an algorithm, but I will then follow-up with the JavaScript equivalent. This is especially helpful when discussing/demonstrating location operations, such as assignment. Create an in-class example of storing values obtained from a user, performing some transformations, storing those results, and displaying this in a Browser window. CMSC 122 What you need to know about the stored program model 8 / 8

Program Abstractions, Language Paradigms. CS152. Chris Pollett. Aug. 27, 2008.

Program Abstractions, Language Paradigms. CS152. Chris Pollett. Aug. 27, 2008. Outline. Abstractions for telling a computer how to do things. Computational Paradigms. Language Definition, Translation.