This is going to be the first post in a series of blog posts on IOS XR code. This post might be simple, but it is a good to start with the basics so that poeple can get familiar with how XR works.
Lets cover the prompt real quick as that is a bit different then what people are used to.
Lets look at the standard IOS prompt vs the IOS XR prompt.
IOS: Router#
IOS-XR: RP/0/7/CPU0:ios#
As you can see the prompt is a bit different. In standard IOS you have the hostname, but in IOS XR you get a bit more information. It breaks down as follows:
Prompt Syntax:
Type – type of interface card (Usually RP for Route Processor)
Rack – What Rack number this is installed in in a multi-shelf system, typically if standalone
Slot – Slot the RP is installed in (7)
Module – What execute the user commands or port interface. Usually CPU0 or CPU1
Name – Hostname of the router, default here is IOS
->  RP/0/7/CPU0:ios#
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Ok, time to get re-familiar with IOS XR code – been some time, worked on IOS for many many years – time to get my hands dirty again.  So based on that, time to share!
 
Let’s start with the basic difference between Cisco IOS and Cisco IOS XR code, the Operating System.
In Cisco IOS, the kernel is monolithic, meaning everything in installed in a single image and all processes share the same address space. There is no memory protection between processes, so if one crashes it can impact all other processes on the box – thus forcing or causing a reload. The other thing with monolithic code is that it has a run to completion scheduler, so the kernel will not preempt a process that is running, the process must make a kernel call before another process has a chance to execute.