Microsoft has offered official confirmation of the fact that Windows Vista Service Pack 1 RTM will start being served via Windows Update today, March 18, 2008. This also means that the gold bits for SP1 will be made available through Microsoft Update and the Microsoft Download Center. Vista end users will be able to grab their copy of the service pack either as a download from WU and MU or as a standalone package from the Download Center. In this manner, March 18 marks a buffer period set in place by the Redmond company following the release to manufacturing of Vista SP1 on February 4, 2008, designed to permit hardware manufacturers to tweak device drivers in order to integrate seamlessly with the service pack.

At the end of the past week, on March 14, 2008, Softpedia revealed that Amazon.com was accepting pre-orders for boxed versions of Windows Vista SP1. The online retailer stated at that time that Vista SP1 packages will be made available on March 19, with the end users being offered the service pack for download on March 18. At that time, Microsoft was still mute on the delivery date of Vista SP1 RTM.

Asked to comment on the release dates posted by Amazon.com, a Microsoft spokesperson said this to Softpedia via email: "when looking at Amazon's site, you will see separate listings - one for pre-orders of Windows Vista with SP1 integrated, and the current version of Windows Vista, which does not include SP1, and can be purchased now and easily updated with SP1 online beginning March 18."

I also asked Microsoft to comment on the Vista SP1 boxes that were featured on Amazon.com. The packagings are similar in design to the boxes for Vista gold, with the sole exception of a label identifying them as having SP1 included. Microsoft did not confirm or deny that the Vista SP1 boxes were the final packagings that would hit the shelves. However, the Redmond company said that Vista SP1 would not be available for retail on March 19.

"The Windows Vista SP1 listing on Amazon.com is a pre-order listing for customers who want to purchase Windows Vista with SP1 to install on new PCs or to upgrade PCs running Windows XP. As we mentioned back in February, some retailers have been planning special promotions on the current version of Windows Vista, which does not include SP1, in advance of the retail availability of Windows Vista with SP1. Some retailers are also accepting pre-orders of Windows Vista with SP1 once it's available," the Microsoft spokesperson added.

UPDATE: Windows Vista Service Pack 1 Five Language Standalone for both 32-bit and 64-bit versions of the operating system is available for download HERE.