The operating system kernel is divided into several parts, called subsystems. The I/O subsystem gives applications access to the computer hardware, gives driver software access to system resources, and manages communications with I/O devices. It acts as the intermediary between the operating system and hardware devices (through their device drivers). Improvements to the Windows XP I/O subsystem make the operating system more stable than in previous versions of Windows and provide for faster performance. Increased stability
Performance is only one factor in selecting an operating system, and in most cases, it's not the most important one. For a production machine, whether it's a desktop client or server, stability and reliability are the top priorities. A fast machine is of little use if it crashes frequently. Microsoft has made some changes to the kernel to increase stability and reduce the chance of system crashes:
- I/O throttling: When the system runs out of memory that can be allocated, it processes I/O information in sequence, one page at a time. This reduces performance but keeps the system from crashing when there is no memory left.
- Drivers are no longer allowed to make "must succeed" requests of the operating system: In earlier Windows versions, the operating system was required to allocate memory to the driver even if memory was low, which could cause a system crash. Even if the driver software does make a "must succeed" request in XP, that request will not be granted.
The APIs for system defragmentation have been rewritten to change the way data is defragmented and improve the defrag process. In Windows 2000, the defragmenter was limited in functionality; for example, encrypted files couldn't be defragged, nor could the Master File Table (MFT). Because the system cache is no longer used by the defragmentation APIs (which required read access), files that are encrypted can now be defragmented. The MFT can be defragged, as well. Another drawback of the W2K defragger was its inability to defrag drives that had large cluster sizes (over 4 KB). This limitation has been removed in Windows XP. It is also possible to mark NTFS files so that they won't be defragged. NTFS improvements
A number of improvements have been made to NTFS that further enhance security, performance, and reliability. The default access control list (ACL) on NTFS volumes is stronger now to improve security. It's now possible to use EFS to encrypt the client-side caching database. Also, the Windows XP Explorer uses the Read-only directory flag to increase performance when the directory contains metadata. If you found this article helpful, check out TechRepublic's TechProGuild subscription resource, which offers in-depth technical articles covering a variety of IT topics, including Windows server and client platforms, Linux, troubleshooting issues, data networking challenges, NetWare, and more. With a TechProGuild account, you can also read the complete text of popular IT industry books online. Sign up now for a free 30-day TechProGuild trial.
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