Understanding XP kernel enhancements

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• XP,
• OS,
• Driver,
• Snapshot

Dr. Thomas Shinder MCSE

Published: 11 Jun 2002 14:47 BST

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Network administrators, IT support pros, and consultants who work with XP will be interested to know what areas of the kernel have been improved for them.

This article continues our focus on four areas of interest to network admins: registry improvements, I/O subsystem enhancements, memory management features, and boot-up. I'll delve into specific enhancements and show you the logic behind the technical wizardry.

Second of two parts -- Last week's article discussed the registry improvements in XP as well as the I/O subsystem enhancements.

Improved fault tolerance
Several of Windows XP's new kernel features support increased fault tolerance. Along with reliability, fault tolerance is an essential component for any mission-critical computer. New or improved fault tolerance features include:

• System Restore
• Improved Driver Rollback
• Shadow copy

System Restore
The System Restore feature (available in Windows XP but not in .Net Server) lets you create checkpoints and then restore the system to the state it was in when the checkpoint was created. This doesn't affect your data files -- common data file extensions like .doc aren't restored, and nothing in the My Documents folder is restored, to prevent overwriting your data.

System Restore uses a file system filter driver named Sr.sys. Restore points are created automatically at set intervals for all drives (you can modify this by changing restore settings) and when specific events take place, such as at the installation of a program. You can also create a checkpoint manually at any time.

Improved Driver Rollback
Driver Rollback support in XP makes it easy to revert to a previous version of a device driver if you install a new driver and find that it ends up causing problems. XP saves a copy of the old driver in a special folder, from which the old driver can be restored to replace the new one.

You can use the Device Manager (accessed via Start | Control Panel | System | Hardware) to roll back a driver. Just locate the device in Device Manager, right-click on it, select Properties, click the Driver tab, and click the Roll Back Driver button.

If the system won't boot into the operating system after you install the new driver, you obviously can't access the Device Manager. In that case, press [F8] during startup to bring up a menu from which you can select the Last Known Good option. This will start the computer with the drivers, as they were, the last time the system booted successfully (that is, with the old driver).

Tip
You can only use Driver Rollback if you've upgraded the driver at least once. Be aware that multiple levels of rollback are not supported; that is, you can only roll back to the previous driver. Also note that Driver Rollback is not available for printer drivers.

Shadow copy
Another new feature in XP is the ability to create a shadow copy as part of the backup process. This is like a snapshot or replica of all files on a volume, even those that are open. This means that a backup can be made while users or programs are accessing the files, and the open files will not be left out of the backup as they were with previous versions of Windows.

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