# Data Representation in a Digital Computer This section outlines how digital computers, which are fundamentally machines with millions of electronic switches, represent complex information using a simple two-state system. ## The Binary Nature of Computers - A *digital computer* is an electronic machine composed of millions of tiny electronic switches. - Like a light switch, each electronic switch has two possible states: - **ON**: Closed, allowing electricity to flow. - **OFF**: Open, preventing the flow of electricity. - This two-state system is represented using the *binary number system*, which has only two digits: **1** and **0**. | Switch State | Electrical State | Binary Representation | | :--- | :--- | :--- | | ON | Current is flowing | **1** | | OFF | No current | **0** | - **Bit**: A single binary digit (a **0** or a **1**) is called a *bit*. It is the most fundamental unit of data in a computer. - **Binary Code**: Data, such as numbers, letters, and symbols, is represented inside a computer by using groups of bits (1s and 0s). For example, the binary code `1000100` might represent the letter 'D'. ## Alphanumeric Codes - *Alphanumeric codes* are standardized binary codes that represent characters. This allows computers to process and store text. - These codes represent a wide range of characters, including: - *Lowercase letters*: a to z - *Uppercase letters*: A to Z - *Numeric digits*: 0 to 9 - *Special characters*: Punctuation and symbols like `%, $, &, #, +`. - ***ASCII (American Standard Code for Information Interchange)***: - This is the most commonly used alphanumeric code. - It uses a 7-bit or 8-bit system to represent up to 128 different characters. ## Electrical Representation of Binary - The circuitry in a digital computer operates on DC voltage. The two binary states (0 and 1) correspond to two distinct voltage levels. - These voltage representations are called *logic levels*: - **Logic 0**: Represents the binary digit **0**, often corresponding to a low voltage level (e.g., 0 Volts). - **Logic 1**: Represents the binary digit **1**, often corresponding to a high voltage level (e.g., +5 Volts). - In practice, these are voltage *ranges*, not exact values. For example: - **Logic 0** might be any voltage from 0V to +0.8V. - **Logic 1** might be any voltage from +2V to +5V. - **Digital Logic Circuits**: These are the circuits within a computer designed to operate on these discrete voltage signals (Logic 0 and Logic 1). **Diagram: Digital Pulse** This diagram shows how voltage levels change over time to represent a sequence of 1s and 0s. The high level (+5V) is Logic 1, and the low level (0V) is Logic 0.