# NT-Lite -- an x86-64 kernel

Boots. Runs processes. Mimics Windows to some extent.

## what is it?

A 64-bit operating system kernel written from scratch. 
UEFI bootloader, physical and virtual memory managers, preemptive scheduler, HAL, VFS, PE loader, partial Win32 layer. 
It boots into a shell. 
~20k lines of C and assembly.

## features

- UEFI bootloader
- physical memory manager
- virtual memory manager with kernel pool
- HAL (screen, keyboard, timer, disk, PCI, APIC)
- preemptive scheduler with priority levels
- processes and threads
- VFS with IRPs
- drive-letter paths (`0:\apps\shell.exe`)
- INI-based boot and driver configuration
- partial Win32 layer (kernel32 and user32, capable of running simple windows apps)
- PE import resolution and dynamic driver loading

## how 2 build

* open env variables
* set `NTLITE_DRIVE` as your thumbdrive (ex. `G:`)
* set `NTLITE_NTPATH` as your thumbdrive (ex. `\\.\PhysicalDrive7`)
* open vs x64 build tools
* cd into this directory
* `build.bat`
* `run.bat`(ide)/`rund.bat`(ide, debug)/`runa.bat`(ahci)/`runad.bat`(ahci, debug)
* enjoy

## how it looks when built

I have some strong opinions on OS design.

```
efi/boot/
  bootx64.efi
boot.ini
hal.dll
colonel.exe
drivers/
  drivers.ini
  ide.sys
  ahci.sys
  fat32.sys
syscall.dll
win32.dll
posix.dll
shell.exe
video.exe
```

## driver model

drivers are PE32+ `.sys` files with an entry point preferably named DriverEntry accepting a constant pointer to HAL_API.

drivers to be loaded have their path stored in `drivers.ini`, split into essential for boot (loaded by bootloader) and not required for boot (loaded by kernel).

a disk driver fills in a `DISK_DRIVER` vtable and calls `IoRegisterDisk(index, &driver)`. 
a filesystem driver fills in an `IO_FILESYSTEM` vtable and calls `IoRegisterFilesystem(index, &fs, &vol)`.

currently shipping: AHCI (interrupts), IDE (PIO/DMA), FAT32 (read-only).

## how it boots

1. UEFI loads `boot.ini`, reads `drivers.ini`
2. bootloader maps kernel, HAL, and boot drivers into the upper half
3. direct physical window at `0xFFFF880000000000`
4. jumps to `KernelMain`
5. PMM, VMM, GDT, IDT, HAL, IRQs, scheduler
6. loads runtime drivers from disk
7. launches `shell.exe`

## paths

```
"apps\shell.exe"     -> drive 0
"0:\apps\shell.exe"  -> drive 0
"2:\data\config.ini" -> drive 2
```

drives 0–7. a drive only works if a filesystem registered on it.

## screenshots

![video.exe running bink video 2](image.png)

## faq

Q: Why?  
A: Why not?

Q: Does it run Doom?  
A: Not yet.

Q: Is the Win32 layer real?  
A: Real enough to load binaries that expect it. Not real enough to run Notepad.

Q: Is the scheduler preemptive?  
A: As much as it will ever be.

Q: Will it corrupt my data?  
A: How would it? It's read-only.

Q: Is this finished?  
A: Not in the slightest.

Q: Can I use this in production?  
A: Don't.