This document provides an overview of the architecture and key components of the Windows XP operating system. It discusses the user mode and kernel mode layers, and how the hardware abstraction layer allows for device-independent programming. It also describes the primary methods of inter-process communication using shared memory and message passing via local procedure calls. Additionally, it outlines the data structures and scheduling used for threads, as well as the demand paging memory management approach used in Windows XP.

1. Windows XP
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Abhishek Gupta

2. Architecture
 Windows XP support Layered approach…
User mode – layer closest to the person
Applications that you run (like Word)
Support programs for applications - the Windows XP Subsystems
Kernel mode – layer closest to hardware
Programs that help software running on our system use the computer’s hardware
Device drivers (software interfaces to hardware)

3.  Hardware Abstraction Layer (HAL) - allow programmers to write device-independent, high
performance applications by providing standard Operating System (OS) calls to
hardware.

5. Inter-process Communication
 Use shared memory and message passing both.
 Message-passing via local procedure call (LPC) facility
 Local Procedure Call - is an internal, inter-process communication facility provided by
the Microsoft for lightweight IPC between processes on the same computer.
 Mailboxes are created for communication for the messages of up to 256 bytes.
 Message larger than 256 byte can be sent using Section Object (shared memory).

6. Threads
 Implements the one-to-one mapping, kernel-level
 Each thread contains a
- thread id
- Register set
- Private data storage area
 The register set, stacks, and private storage area are known as the context of the threads.

7. Primary Data Structure of Threads
 Kernel level
- ETHREAD (executive thread block)
- KTHREAD (kernel thread block)
 User level
- TEB (thread environment block)

8. Scheduling
 Windows uses priority-based preemptive scheduling
 Highest-priority thread runs next
 Thread runs until (1) blocks, (2) uses time slice, (3) preempted by higher-priority thread
 Real-time threads can preempt non-real-time

9. Memory Management
 Uses demand paging with clustering. Clustering brings in pages surrounding the faulting page
 Processes are assigned working set minimum and working set maximum
 Working set minimum is the minimum number of pages the process is guaranteed to have in
memory
 A process may be assigned as many pages up to its working set maximum
 When the amount of free memory in the system falls below a threshold, automatic working set
trimming is performed to restore the amount of free memory
 Working set trimming removes pages from processes that have pages in excess of their working
set minimum