PC11 — a tiny experimental OS (v0.2)

PC11 is a small, from-scratch operating system for modern PCs. It boots via UEFI into 64-bit (x86-64) long mode and runs a graphical window manager with several built-in apps — everything is software-rendered to the UEFI GOP framebuffer, with input read directly from the PS/2 mouse and the UEFI keyboard. It builds into a single bootable pc11.iso that runs in QEMU or on real UEFI hardware.

Features

System

• Boots as a UEFI application (BOOTX64.EFI) — no BIOS, no legacy bootloader.
• 64-bit graphics drawn straight to the UEFI GOP linear framebuffer.
• Requests a 1920×1080 display mode at startup (falls back to the firmware's current mode if 1080p isn't available). The whole UI is resolution-independent — it reads the actual framebuffer size at boot.
• Ships as a single bootable hybrid ISO (pc11.iso) — works in QEMU and, written to a USB stick (dd if=pc11.iso of=/dev/sdX), on real PCs.
• Crash screen: a CPU exception handler (custom IDT) catches faults, shows PC11 has crashed :( with the error number + name + error code, counts down 5 seconds, then automatically reboots — instead of a silent triple-fault reboot.
• The UEFI watchdog timer is disabled at startup, so PC11 keeps running indefinitely (the firmware would otherwise force-reboot after ~5 minutes).

Desktop & window manager

• Desktop with a bottom taskbar: a Start button showing the PC11 icon, one entry per open window, and a live clock.
• The Start-button icon is a real PNG (PC11/logo.png) decoded at boot and smoothly area-scaled (alpha-weighted, anti-aliased) into the button.
• Start menu pops up from the taskbar listing every app; Power Off is pinned at the bottom, below a separator.
• Windows have rounded corners and anti-aliased text. You can:
  • move them (drag the title bar),
  • resize them (drag the bottom-right grip),
  • minimize [-] and close [x] via title-bar buttons,
  • focus/raise by clicking (proper z-order),
  • restore/raise from the taskbar.
• A custom desktop wallpaper can be set from an image (see Files).

Apps

• About PC11 — info about the system.
• Files — a real file manager:
  • enumerates the actual disk volumes (drives),
  • browses real folders, descends into subdirectories, goes up with [..] / the Up button,
  • previews file contents (text-wrapped inside the window),
  • New creates and Del deletes real files,
  • reads/writes the live filesystem via UEFI (boot services stay alive).
  • Right-click a file (or the desktop) for a context menu: Copy, Edit, Set as BG (images only), Paste.
  • Copy/Paste duplicates real files: copy a file, navigate elsewhere, then paste to write a real copy there.
  • Set as Background decodes an image and uses it as the wallpaper. Formats, all via from-scratch decoders: PNG (8-bit RGB/RGBA, non-interlaced), JPG/JPEG (baseline sequential), BMP (24/32-bit).
• Editor — a text editor that:
  • Open button lists files in the current folder to pick one,
  • or open a file from the Files right-click → Edit,
  • edit the text, and Save writes it back to the real disk.
• Terminal — a command shell: help, ver, echo, about, clear.
• Calculator — a working calculator with a clickable keypad (digits, + - * /, C, =).
• Clock — shows the current time and date from the hardware RTC.
• Power Off — Shut Down and Restart (UEFI Runtime Services ResetSystem).

Input

• Mouse via direct PS/2 port polling (left + right buttons).
• Keyboard via the UEFI console (ConIn).
• (Boot services are kept alive so the file manager can read real disks on demand; the PS/2 mouse is polled directly because the UEFI pointer protocol is unreliable under OVMF.)

Performance

Everything is software-rendered, so the renderer is tuned to stay responsive even at 1080p:

• The scaled wallpaper is cached (DESK buffer) and only rebuilt when the wallpaper or resolution changes — moving the mouse no longer re-scales ~2 million pixels every frame.
• The desktop copy and the back-buffer→framebuffer blit use bulk (word-at-a-time) memcpy instead of scalar per-pixel loops.
• The renderer only redraws on actual input/activity and idles otherwise.
• run.sh compiles with -O2, which substantially speeds up the pixel-pushing loops (fonts, windows, icon, scaling).

Files

File	Purpose
PC11/wm.c	The window manager and all apps.
PC11/efi.h	Minimal freestanding UEFI definitions.
PC11/font8x8.h	8x8 bitmap font (ASCII), drawn anti-aliased.
PC11/logo.png	The PC11 Start-button icon (decoded + scaled at boot).
PC11/png.h	From-scratch PNG (+ DEFLATE/inflate) decoder.
PC11/jpg.h	From-scratch baseline JPEG decoder.
PC11/crash.h	CPU exception handling for the crash screen.
run.sh	Builds pc11.iso and boots it in QEMU + OVMF.
home/	Files placed on the disk, shown in the Files app as /home (e.g. home/documents, home/pictures).

Build & run

You need a PE/EFI-capable compiler, mtools, xorriso, QEMU, and OVMF (UEFI) firmware. run.sh is a bash script that auto-detects the toolchain and firmware and prints the exact install command if something is missing.

Linux

• Arch: sudo pacman -S --needed mingw-w64-gcc mtools libisoburn qemu-desktop edk2-ovmf
• Debian/Ubuntu: sudo apt-get install -y gcc-mingw-w64-x86-64 mtools xorriso qemu-system-x86 ovmf
• Fedora: sudo dnf install -y mingw64-gcc mtools xorriso qemu-system-x86 edk2-ovmf

macOS (Homebrew)

brew install mingw-w64 mtools xorriso qemu

Windows

Run the script from a Unix-like shell. Two options:

1. WSL (recommended) — install Ubuntu from the Microsoft Store, then follow the Debian/Ubuntu line above and run ./run.sh inside WSL.
2. MSYS2 — install MSYS2, open the MSYS2 MinGW x64 shell, then:

   pacman -S --needed mingw-w64-x86_64-gcc mtools xorriso

   Install QEMU for Windows (https://qemu.weilnetz.de/w64/) — it bundles the OVMF firmware (edk2-x86_64-code.fd). run.sh automatically adds the default install dirs (e.g. C:\Program Files\qemu) to its search path and finds both the qemu-system-x86_64.exe binary and the bundled firmware.

Then, on any platform:

./run.sh

run.sh compiles PC11/wm.c, builds a FAT EFI System Partition, wraps it into a single bootable pc11.iso, finds your OVMF firmware automatically, and boots the ISO under QEMU. All intermediate files are created in a temp dir and removed — the only output is pc11.iso.

To put it on real hardware (⚠️ erases the target):

# Linux/macOS:
sudo dd if=pc11.iso of=/dev/sdX bs=4M status=progress
# Windows: write pc11.iso to a USB stick with Rufus or balenaEtcher.

Controls

• Start button (bottom-left, the PC11 icon): open the Start menu, then click an app to launch it. Power Off is pinned at the bottom of the menu.
• Mouse: move the cursor; left-click a window to focus/raise it; drag the title bar to move; drag the bottom-right grip to resize; click [-] to minimize and [x] to close. Right-click a file (or the desktop) for the Copy / Edit / Set-as-BG / Paste context menu.
• Taskbar: click an entry to restore/raise that window.
• Keyboard: Tab cycles focus; arrow keys move the focused window (or navigate the Files list); type into the Terminal/Editor when focused; Esc clears the screen and halts.

How it works

PC11 uses UEFI: the firmware (OVMF under QEMU) loads EFI/BOOT/BOOTX64.EFI already in 64-bit mode and hands us a graphics framebuffer via the Graphics Output Protocol (GOP).

At startup PC11:

1. Disables the UEFI watchdog timer (otherwise the firmware reboots after ~5 minutes).
2. Installs a small IDT (copying the firmware's, overlaying only the CPU-exception vectors) so faults reach the crash screen while normal interrupts keep working.
3. Locates the GOP framebuffer, selects a 1920×1080 mode if available (otherwise keeps the current one), and allocates a back buffer plus a cached-desktop buffer.
4. Keeps UEFI boot services alive so the Files app can read real disks on demand (Simple File System + File protocols).
5. Reads the keyboard through the UEFI console (ConIn) and the mouse by polling the PS/2 controller (i8042, ports 0x60/0x64).
6. Runs the window-manager loop: copy the cached desktop (the wallpaper is scaled only when it changes), draw windows and the cursor into the back buffer, then bulk-memcpy it to the framebuffer.

Power off / restart use UEFI Runtime Services (ResetSystem).

Status

Experimental, v0.2 — a learning/hobby OS, not a general-purpose system. Image support is limited to common cases (8-bit PNG, baseline JPEG, uncompressed BMP); the disk filesystem is whatever UEFI exposes (FAT).