OS Interface

gistfile1.txt

OS Interface:

It has a layered interface.

It needs to work on different platforms, such the TR3200, the DCPU-16 and the DCPU-16e. 

Therefore it needs to split the following up:

User mode user processes (Layer 4)
User mode system processes (layer 3)
Architecture-independent kernel code (layer 2)
Architecture-specific kernel code (layer 1)

Standalone object code archives that the kernel can load at runtime are called "extensions" as a whole. 

The 2-1 interface is called the "driver interface", and level 1 extensions are called "drivers".
The 2-2 interface is called the "module interface", and level 2 extensions are called "modules".
The 2-3 interface is called the "service interface", and level 3 extensions are called "services".

Drivers and modules run in kernel mode. Services run in user mode.
Drivers are architecture-specific. Modules and services are architecture-independent.

Drivers are architecture-specific extensions that run in kernel mode.
Modules are architecture-independent extensions that run in kernel mode.
Services are architecture-independent extensions that run in user mode.

You would write a driver over a module when you need access to hardware and/or architecture-specific facilities.
You would write a module over a driver when your extension has general applicability over multiple architectures.
You would write a module over a service for performance reasons, or because you must do something privileged to the kernel.
You would write a service over a module if some context switching won't hurt performance too badly, performance isn't critical, and you want the security of being unable to crash the system.