Noureddine RAMDI / ZealOS: a modern fork of TempleOS with ZealC and 60 FPS graphics

Created Sat, 23 May 2026 20:41:14 +0000 Modified Sat, 23 May 2026 20:41:27 +0000
1023 Words
github-stars operating-system zealc templeos vbe-graphics ahci uefi

Zeal-Operating-System/ZealOS

ZealOS is a rare breed of operating system project: a public-domain, single-developer comprehensible OS that builds directly on the legacy of TempleOS — Terry Davis’s famously idiosyncratic 64-bit OS. It modernizes TempleOS by forking its unique C-like language HolyC into ZealC, targets smooth 60 FPS VBE graphics at variable resolutions, and adds real hardware support features like AHCI, all while maintaining radical simplicity.

what ZealOS is and how it builds on TempleOS

ZealOS is a public-domain operating system forked from TempleOS, designed to preserve the core philosophy of Terry Davis’s work: an OS simple enough that a single person can understand the entire codebase within days. It is written in ZealC, a language renamed and forked from HolyC, TempleOS’s original scripting and systems language. This language is essentially C-like but tailored specifically for OS development, combining low-level control with simplicity.

The OS runs as a 64-bit system with ring-0 execution for all operations, meaning there is no memory protection or separation between user and kernel space. This radical design choice keeps the system small and comprehensible, but also limits it from being suitable for multi-user or high-security environments.

ZealOS targets 60 FPS graphics using the VESA BIOS Extensions (VBE) standard, supporting variable screen resolutions. This is an upgrade over TempleOS’s fixed 640x480 display and aims for smoother graphical output suitable for modern display hardware.

Under the hood, ZealOS adds support for AHCI (Advanced Host Controller Interface) to enable modern SATA device handling, a clear step towards usability on real hardware beyond the original TempleOS environment. The project is also working towards adding network drivers and a UEFI bootloader, which will further modernize its hardware compatibility.

technical strengths and design tradeoffs

What sets ZealOS apart is its commitment to maintain a single-person-comprehensible codebase while modernizing key areas that TempleOS left behind. The fork from HolyC to ZealC is not trivial — it involves improving code readability with better comments and documentation, making the system more approachable for new contributors without sacrificing minimalism.

The choice to keep everything ring-0 and avoid memory protection is consistent with TempleOS’s philosophy but is a tradeoff. This makes the OS much simpler and faster in certain respects, but it also means it cannot run untrusted code safely or provide the security guarantees modern multi-user systems require.

The graphics subsystem targeting 60 FPS at variable resolutions is a technical highlight. It shows a practical application of VBE graphics programming, which is not commonly targeted in hobby OS projects. Achieving smooth frame rates on bare-metal graphics without a complex driver stack is no small feat.

Code quality is surprisingly clean given the scope and solo nature of the project. The codebase includes inline comments and documentation that clarify the intent behind many low-level routines. This is key for a project that intends to be studied and extended by a single developer or a small group.

The ongoing work on network drivers and a UEFI bootloader indicates a path toward making ZealOS more practical for actual hardware use, though these components are still in development and not yet production-ready.

quick start with ZealOS

The project provides a clear Getting Started guide in its README, requiring a few prerequisites:

  • Intel VT-x or AMD-V virtualization support enabled in BIOS. This is necessary to properly virtualize the 64-bit OS.
  • On Windows systems, Hyper-V must be enabled.
  • A working knowledge of the C programming language is recommended to understand and modify the OS.

To create a Distro ISO image of ZealOS, the project includes a build-iso script. The README points to the Wiki for detailed instructions on building the ISO image.

Once the ISO is created, you can install ZealOS on virtual machines such as VirtualBox or VMWare, or even install it on bare-metal hardware. The Wiki contains installation guides for these platforms.

Contributions are encouraged and can be done in two ways:

  1. Inside the OS itself, following Terry Davis’s intended workflow: make changes after booting the latest ISO in a VM, then run the sync script to merge changes back to the repo.

  2. Using an external text editor on the cloned repository files, then submitting pull requests.

This dual approach supports both immersive OS-level development and conventional source control workflows.

verdict

ZealOS is a niche but fascinating project for those interested in operating system design that prioritizes minimalism and comprehensibility over security and multi-user support. It is a modern continuation of TempleOS with practical hardware improvements and a cleaner codebase.

It’s best suited for hobbyists, OS enthusiasts, and developers curious about a radical approach to OS design where one person can realistically grasp the entire system. The lack of memory protection and security features means it is not suitable for production or general-purpose use.

The project is worth exploring if you want a deep dive into a unique OS architecture and language design (ZealC) that blends systems programming with radical simplicity. The clear documentation and active development make it accessible for those with a solid C background and interest in low-level programming.

If you want a contemporary take on Terry Davis’s vision with some modern hardware support and 60 FPS graphics, ZealOS is a rare open source project to watch.

→ GitHub Repo: Zeal-Operating-System/ZealOS ⭐ 2,300 · HolyC