Kernel enhancements are often seen as only of interest to developers. Administrators may wonder, what’s in it for me? In this Daily Drill Down, I’ll explain some of the more significant improvements Microsoft has made to the XP/.NET kernel and, more importantly, what these changes mean to you—even if you’re not a programmer. The new kernel features I’ll discuss can be broken down into four categories:
1. Registry improvements
2. Beefed-up I/O subsystem
3. New memory management features
4. Faster boot-up
Registry improvements
The registry serves an important function in all Microsoft
operating systems from Windows 95 forward. In each new operating system version,
Microsoft has refined the functionality of the registry, adding new subkeys and
entries to give administrators even more control over the behavior of the
operating system.
The XP/.NET registry code provides a couple of practical benefits to users and administrators: The registry can be larger than in previous versions of Windows, and registry queries are faster.
Support for larger registry size
In previous versions of Windows, the size of the registry was limited to about 80 percent of the paged pool size. This generally meant a registry size limit of about 376 MB.
Windows XP/.NET has removed this limitation. The registry has been moved out of the paged pool; XP uses the Memory Cache Manager to map the registry, in chunks of 256 KB, into the system cache. Now the total registry size is limited only by the amount of disk space available. The system hive, however, still has a maximum size, but it has been increased from 12 MB to 200 MB.
Support for faster queries
Queries to the registry are processed faster in XP, due to the caching performed by the Memory Cache Manager and the way registry information is stored. With earlier Windows versions, when a new registry subkey was created, it was stored in the first available space located. XP uses a more organized approach, placing all related subkeys into the same physical group, located contiguous to one another. This reduces the number of page faults that occur when accessing registry information.
Windows XP further speeds up query time by caching registry keys so that they can be accessed faster. XP is able to monitor the usage of registry keys by applications, so that the keys that are needed are already in memory.
Beefed-up I/O subsystem
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:
Defragger on steroids
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.
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