What was the code name for 64-bit Windows?

Raymond Chen

The code name for the effort to port Windows from 32-bit to 64-bit was Sundown. Although the intended target was Intel’s Itanium architecture, the initial effort was to port 32-bit Windows to the 64-bit Alpha AXP. At the time, Itanium chips existed only in simulators. but Alpha AXP chips had been in production for years, and there was a glut of unused Alpha AXP systems among Microsoft Windows developers.

The code name for the 64-bit Windows project was Sundown.

I hadn’t given the code name much thought. Lots of projects have code names, and you rarely think deeply about the name. It’s just an arbitrary collection of words to identify a project.

It wasn’t until the ship party that I realized that the code name actually meant something. The project lead went on stage to thank everyone for their hard work and congratulate them on a job well done, and then finished the speech by announcing Sun? Down!

It was then that I realized that the code name of “Sundown” was not chosen arbitrarily. It was a jab at Sun Microsystems, who had recently released Solaris 7, a 64-bit operating system built on the UltraSPARC processor. The 64-bit version of Windows was a direct attack against Sun’s early foothold, with the goal of unseating the current leader.

Today, the leading 64-bit operating system is neither Solaris nor Windows. It’s Android: As of 2020, over 80% of adults in the world own a smartphone, over 70% of smartphones are running Android, and nearly 90% of Android devices use ARM64.


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  • Dmitry 0

    0.8 × 0.7 × 0.9 is only slightly more than 50% of adults. And as adults don’t restrict themselves to using only smartphones, it’s quite possible that a desktop OS (we don’t use names here, right?) might have even larger market share at the same time but in a different segment.

    • Antonio Rodríguez 1

      Personally, I’m tired of all these “usage quota wars”. 2024 is going to be the year of a certain OS whose mascot is an stuffed arctic animal. As it was going to be 2023, and 2022, and 2021… And the company whose logo is a bitten fruit used to shout its two-digit year-over-year gains in quota back when it was recovering from nearly dead in the late 90s (and stopped doing so when it touched its own ceiling and stopped growing, of course). All this reminds me of high school pep rallies (see XKCD comic number 588). My OS is better than yours because it has more users. Isn’t it? Right?

      Well, I think we all are Engineers (yes, with a capital “E”). We should select a product or technology based on its ability to solve the problem we have at hand and, perhaps, our level of expertise with it. I don’t think usage quota has anything to do with either.

  • Joe Beans 4

    The number one 64-bit platform could have been Windows Phone 10 but our favorite CEO threw the race and burned it all down. We were told there were no apps but honestly you only need a dozen good developers to write all the phone apps the world needs, or even better, generalize the functionality as WP did so the UI only has to be written once and every service becomes a headless plugin. What a shame. Android is such obfuscated garbage, a maze whose walls always keep changing.

    • Andrew Brehm 2

      Exactly! I loved Windows Phone 10. And lots of colleagues used it or wanted to use it next or were simply interested and would have used it. I always wonder what made MSFT keep changing their strategy…

    • Zak Larue-Buckley 0

      Microsoft were in a prime position for the coming smartphone OS wars.

      All of the developers were already writing for PocketPC devices. It had a huge number of apps.

      Then Windows Mobile 6 and 6.5 feel behind the curve with a stylus based UI.

      Then for Windows Phone 7 someone decided that development tools were .Net only so nobody bothered developing software for it. And the rest was history…

  • Yuhong Bao 0

    Which also reminds me of MS OS/2 2.0 and DR-DOS.

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