Code

1. Codes are essential for communication between people and machines.

In this book, the word code usually means a system for transferring information among people and machines.

Communication is key. Codes are systems that allow the transfer of information, whether between individuals or between humans and machines. They are the foundation of communication, enabling the expression and understanding of data.

Examples of codes:

• Morse code: Uses dots and dashes to represent letters and numbers.
• Braille: Uses raised dots to represent letters for the visually impaired.
• Spoken language: Uses sounds to form words and convey meaning.
• Written language: Uses symbols to represent words on paper.

Codes serve specific purposes. Different codes are useful in different contexts. Morse code allows for silent communication over distances, while Braille enables reading for the blind. The choice of code depends on the needs and limitations of the communicators.

2. Binary code is fundamental to computers, representing information with two states.

The key word here is two. Two types of blinks, two vowel sounds, two different anything, really, can with suitable combinations convey all types of information.

Binary simplifies representation. Binary code, with its two states (0 and 1), is the simplest and most efficient way for computers to represent information. These states can be easily implemented using electrical signals, switches, or other physical phenomena.

Combinatorial analysis. By combining bits, computers can represent a vast range of information. The number of possible combinations grows exponentially with the number of bits. For example:

• 1 bit: 2 combinations (0, 1)
• 2 bits: 4 combinations (00, 01, 10, 11)
• 3 bits: 8 combinations (000, 001, 010, 011, 100, 101, 110, 111)

Bits as building blocks. The bit is the fundamental unit of information in computing. More complex data, such as numbers, text, images, and sounds, are all ultimately represented as sequences of bits.

3. Electricity, controlled by switches and relays, forms the hardware basis of computation.

The flashlight is certainly one of the simpler electrical appliances found in most homes.

Electricity enables computation. The flow of electrons through circuits is the physical basis of computation. By controlling this flow with switches and relays, we can create circuits that perform logical operations.

Basic electrical concepts:

• Voltage: The potential for doing work, measured in volts.
• Current: The flow of electrons, measured in amperes.
• Resistance: The opposition to the flow of electrons, measured in ohms.

Switches and relays as control elements. Switches allow us to manually control the flow of electricity, while relays use an electrical signal to control a switch. Relays can be used to amplify signals or to create remote-controlled switches.

4. Number systems beyond decimal, especially binary, are crucial for digital systems.

Fortunately, we don’t have to actually write out all the possible codes to determine how many there would be.

Decimal limitations. While humans typically use the decimal (base-10) number system, it is not inherently superior to other systems. The choice of base-10 is likely due to the number of fingers on our hands.

Alternative number systems:

• Octal (base-8): Uses digits 0-7.
• Quaternary (base-4): Uses digits 0-3.
• Binary (base-2): Uses digits 0 and 1.

Binary's importance. The binary number system is particularly important in computing because it aligns directly with the two states of electrical switches (on/off, 1/0). This makes it easy to represent and manipulate numbers using electronic circuits.

5. Boolean algebra and logic gates provide the mathematical foundation for computer circuits.

The relay is a remarkable device. It’s a switch, surely, but a switch that’s turned on and off not by human hands but by a current.

Boolean algebra and logic. Boolean algebra, with its operators AND, OR, and NOT, provides a mathematical framework for describing logical operations. These operations can be implemented using electrical circuits called logic gates.

Basic logic gates:

• AND gate: Output is 1 only if both inputs are 1.
• OR gate: Output is 1 if either input is 1.
• NOT gate (Inverter): Output is the inverse of the input.
• NAND gate: Output is 1 only if both inputs are 1.
• NOR gate: Output is 1 if either input is 1.
• XOR gate: Output is 1 if either input is 1, but not both.

Logic gates as building blocks. By combining logic gates, we can create circuits that perform more complex logical operations. These circuits can be used to implement arithmetic operations, control systems, and other computational tasks.

6. Memory, implemented with flip-flops, allows computers to store and retrieve information.

The device we’ve invented is called a repeater, or a relay.

Flip-flops as memory elements. A flip-flop is a circuit that can store one bit of information. It has two stable states, representing 0 and 1, and can be switched between these states by applying appropriate input signals.

Types of flip-flops:

• R-S flip-flop: Basic flip-flop with Set and Reset inputs.
• D-type flip-flop: Stores the value of the Data input when the Clock signal is asserted.
• Edge-triggered D-type flip-flop: Stores the value of the Data input only at the instant the Clock signal transitions from 0 to 1.

Memory arrays. By combining multiple flip-flops, we can create memory arrays that store multiple bits of information. These arrays can be organized as read/write memory (RAM) or read-only memory (ROM).

7. Microprocessors integrate processing units onto a single chip, revolutionizing computing.

The invention of the telegraph truly marks the beginning of modern communication.

Microprocessors as CPUs. A microprocessor is a single integrated circuit that contains all the essential components of a central processing unit (CPU). This includes the arithmetic logic unit (ALU), registers, and control logic.

Key microprocessor characteristics:

• Data width: The number of bits that the processor can process at a time (e.g., 8-bit, 16-bit, 32-bit).
• Clock speed: The rate at which the processor executes instructions, measured in hertz (Hz).
• Addressable memory: The amount of memory that the processor can access.

Impact of the microprocessor. The development of the microprocessor revolutionized computing by making it possible to create small, affordable, and powerful computers. This led to the personal computer revolution and the widespread adoption of computers in all aspects of life.

8. Operating systems manage computer resources and provide a user interface.

I want Code to be a book that makes you understand these things, not in some abstract way, but with a depth that just might even rival that of electrical engineers and programmers.

Operating systems as resource managers. An operating system (OS) is a collection of software that manages the hardware resources of a computer and provides a set of services to application programs.

Key functions of an operating system:

• File system: Organizes and manages files on storage devices.
• Memory management: Allocates and manages memory for programs.
• Input/output (I/O) management: Provides a standardized interface for programs to access peripherals.
• User interface: Provides a way for users to interact with the computer.

Examples of operating systems: CP/M, MS-DOS, UNIX, Linux, macOS, Windows.

9. Character encoding standards like ASCII and Unicode enable text representation.

Although Morse code has absolutely nothing to do with computers, becoming familiar with the nature of codes is an essential preliminary to achieving a deep understanding of the hidden languages and inner structures of computer hardware and software.

Character encoding is essential. To represent text in computers, we need a system that assigns a unique code to each character. These codes are then stored as bits in memory.

Character encoding standards:

• ASCII: A 7-bit code that represents 128 characters, including letters, numbers, punctuation marks, and control characters.
• Extended ASCII: 8-bit extensions of ASCII that provide additional characters, such as accented letters.
• Unicode: A 16-bit code that represents over 65,000 characters, encompassing most of the world's writing systems.

Importance of standards. Standardized character encoding systems are crucial for ensuring that text can be exchanged and displayed correctly across different computers and platforms.

10. The evolution of computing involves a progression from mechanical to electronic devices.

Code rattled around in my head for about a decade before I started writing it.

From abaci to chips. The history of computing is a story of continuous innovation, from the earliest mechanical calculating devices to the sophisticated electronic computers of today.

Key milestones in computing history:

• Abacus: An ancient counting tool.
• Napier's Bones: A mechanical aid for multiplication.
• Pascaline and Leibniz's calculator: Early mechanical calculators.
• Jacquard loom: Used punched cards to automate weaving patterns.
• Babbage's Analytical Engine: A conceptual precursor to modern computers.
• Hollerith's tabulating machine: Used punch cards to process census data.
• Electromechanical computers: Used relays to perform calculations.
• Electronic computers: Used vacuum tubes and transistors to perform calculations.
• Microprocessors: Integrated all the components of a CPU onto a single chip.

The future of computing. The trend toward smaller, faster, and more powerful computers is likely to continue. New technologies, such as quantum computing and nanotechnology, may lead to even more revolutionary changes in the future.

Last updated: February 17, 2025