What's SP1a and what's the difference between SP1 and SP1a?
On February 3, 2003, Microsoft released SP1 again as SP1a. Just like SP1, SP1a is a collection of updates for Windows XP. Windows XP SP1a is the same as Windows XP SP1 except that the Microsoft virtual machine (VM) is removed in SP1a. There are no other changes or fixes included in this update.
Go to the SP1a official web site
If you are not running Windows XP SP1, install SP1a to make sure that you have the latest security and reliability updates for Windows XP. Install any appropriate security updates and hotfixes that are already released or that will be released after SP1 on Windows XP-based computers that are running SP1a. Windows Update will continue to offer the same set of updates for Windows XP-based computers that are running either SP1 or SP1a.
To determine if you are running Windows XP SP1, right-click My Computer, and then click Properties. If "Service Pack 1" appears under System, you are already running Windows XP SP1. There is no benefit to installing SP1a if you are already running Windows XP SP1. Microsoft does not recommend that you install SP1a if you are already running SP1. Note: If you are running Windows XP or Windows XP SP1 with the Microsoft VM, you can continue to update the Microsoft VM by using Windows Update. If you are running Windows XP without the Microsoft VM, you do not have to install updates to the Microsoft VM. Therefore, these updates are not offered to you when you visit Windows Update. Microsoft is no longer able to provide a download of the Microsoft VM for computers that do not already have the Microsoft VM installed.
To determine if you are running the Microsoft VM, follow these steps:
Click Start, and then click Run.
Type cmd, and then click OK.
At the command prompt, type jview and then press ENTER.
If you are not running the Microsoft VM, you receive the following error message:
\jview\ is not recognized as an internal or external command, operable program or batch file.
When you install Windows XP SP1a, the following changes are made to the registry. These changes indicate that SP1a is installed:
A string value is created in the following registry key and its value data is set to "a":
The value data for the Description string value in the following registry key is updated to include "SP1a":
The title for the Windows XP Service Pack 1 entry in the Add or Remove Programs tool in Control Panel is changed to "Windows XP Service Pack 1a."
To download SP1a for Windows XP:
The Network Installation is ideal for IT professionals installing SP1 on multiple computers. Get more information about SP1a and instructions on how to deploy it.
SP1a Express Installation (typically ~30mb)
Use the Express installation if you have only one computer to upgrade to SP1a. Get more information about SP1a and instructions on how to install it. The Express installation checks your computer and installs only the files that are necessary to bring your computer up to date. As a result, the number of files installed and the time required may be less for computers that already have Windows XP hotfixes installed.
Read Windows XP SP1 Info for more info on SP1.