Use a Code Editor (Not a Word Processor) for CPUSim64

CPUSim64 programs are plain-text source files. A code editor helps you write clean, correct assembly code, while a word processor can silently change your text in ways that break assembly.

Why a word processor is the wrong tool

Word processors (like LibreOffice Writer, Apple Pages or Microsoft Word) are designed for formatted documents, not source code. They may automatically “help” by converting straight quotes to smart quotes, replacing hyphens with em dashes, changing indentation, or inserting hidden formatting characters. In assembly language, those tiny changes matter: a single unexpected character can turn a correct instruction into a syntax error.

CPUSim64 assembly relies on exact spelling, exact punctuation, predictable whitespace, and reliable line endings. A code editor preserves your file as plain text and gives you tools that make programming easier—syntax highlighting, line numbers, indentation control, search/replace, and often optional features like bracket matching and integrated terminals.

CPUSim64 source files must be saved as plain text (ASCII or UTF-8) and avoid “smart quotes” and auto-correction features that can alter punctuation.

What to look for in a CPUSim64-friendly editor

Plain-text editing (no hidden formatting)
Monospace fonts and consistent indentation
Line numbers (very helpful when debugging assembly errors)
Syntax highlighting (optional, but makes code easier to read)
Good search/replace (quickly refactor labels and constants)

Recommended editors by platform

Cross-platform

Visual Studio Code — A popular, free editor for Windows, macOS, and Linux with excellent search, extensions, and an integrated terminal. It’s a great “all-around” choice if you want a modern UI and lots of customization.
Sublime Text — Fast, lightweight, and polished across all major platforms. It’s especially nice if you want speed and a clean, distraction-free editor that still has powerful editing features.
Kate — A solid graphical editor commonly found on Linux desktops, offering features like split views, sessions, and convenient project/file browsing.
UltraEdit — A mature, feature-rich editor often used for large files and serious text work. It’s a solid choice if you want lots of built-in capabilities without moving to a full IDE.
Zed — A newer, performance-focused editor with a modern feel. If you like a clean UI and quick navigation, it’s worth a look (availability may vary by platform and release).

Linux favorites

Vim — A legendary modal editor available on Linux (and also other platforms). Vim is powerful for keyboard-driven editing, macros, and rapid navigation once you learn the basics.
GNU Emacs — Another classic editor with a deep ecosystem. Emacs can be configured into a full programming environment, and many developers love its extensibility and workflows.
Gedit — Gedit is the default text editor for the GNOME desktop and emphasizes simplicity and reliability. It is ideal for CPUSim64 beginners who want a clean, distraction-free editor that safely edits plain text while still providing essentials like line numbering and search/replace.

macOS standouts

BBEdit — A long-time favorite on macOS for working with plain text. It’s reliable, fast, and has excellent tools for search/replace, file management, and working with source code without “helpful” formatting surprises.
TextMate — A macOS-native editor known for its simplicity and speed. It’s a great option if you want something lighter than a full IDE.

Windows essentials

Notepad++ — A classic Windows editor that’s lightweight and practical, with tabs, plugins, and helpful tooling for plain-text code editing.

EditPad Lite / EditPad Pro

PSPad — PSPad is a free Windows-only editor aimed at developers. It includes syntax highlighting, macro support, a built-in hex editor, and project management features, all while remaining lightweight.

Legend:

Free & Open Source

Free but Proprietary

Paid Proprietary

Free/Paid Proprietary

Pick an editor you’re comfortable with—just make sure it edits plain text. That single choice will prevent a lot of mysterious assembly errors.

A quick “word processor damage” example

If a word processor silently converts quotes or hyphens, your code may look normal on screen but fail to assemble. For example, smart quotes (“ ”) are different characters than plain quotes (" ").

; Good (plain ASCII quotes)
PRINT "Hello, CPUSim64!"

; Bad (smart quotes inserted by a word processor)
PRINT “Hello, CPUSim64!”

Want a CPUSim64 syntax highlighting file for your favorite editor (VS Code, Sublime, Vim, etc.)? That’s doable—and it makes assembly even easier to read.