Many digital archivists have uploaded verified hashes of Build 21390. Look for uploads including SHA-1 checksums. Always verify file integrity using CertUtil or 7-Zip.
Red flags to avoid:
| Threat Vector | Description |
|---------------|-------------|
| Pre-ransomware vulnerability | Unpatched SMB, RDP, and printer spooler exploits |
| Timebomb activation | System becomes unusable or resets every few hours |
| Telemetry from Microsoft | Insider builds still send diagnostic data |
| Trojanized ISOs | Attackers embed backdoors (e.g., modified install.wim with hidden admin account) |
| Expired certificates | Drivers and apps may fail to install or run |
| No Windows Update | Cannot get any security fixes, even for Defender definitions (unless manually updated via offline .cab) |
The build included background intelligence transfer efficiency tweaks, reducing download sizes by up to 15% compared to Build 21382.
Since Build 21390 has expired (October 2021), Microsoft no longer serves it via Windows Update. However, if you have an MSDN (Visual Studio) subscription, legacy builds are sometimes archived.
Crucially, Build 21390 still featured:
For users who despise Windows 11’s centered taskbar and simplified context menus, this build is a time capsule.
Disclaimer: Unauthorized distribution of Microsoft copyrighted ISOs is illegal. Below are official or sanctioned sources.
Windows 10 Insider Preview Build 21390 (x86 / x64) ISO represents a unique moment in Microsoft’s history – the end of the classic Windows 10 experience and the quiet beginning of Windows 11’s development. While it is an expired, unsupported build, its value for virtual machines, legacy hardware, and nostalgic users is undeniable.
When searching for this ISO, prioritize legitimate tools like UUP Dump to generate a clean copy directly from Microsoft’s servers. Always verify checksums, and never run random EXE files from torrent sites. Whether you’re a developer seeking a test environment or a power user longing for a simpler taskbar, Build 21390 delivers the last true taste of the Windows you remember.
Have you installed Build 21390 on unusual hardware? Share your experience in the comments below!
The Exciting New Build
It was a typical Monday morning for Microsoft's Insider team. They had been working tirelessly over the weekend to push out a new build to the Windows 10 Insiders. As the team lead, Brandon, walked into the office, he couldn't help but feel a sense of excitement. Today was the day they would release Build 21390 to the world.
The team had been working on this build for weeks, and it was packed with new features and fixes. They had made significant improvements to the UI, updated the Settings app, and even added some new functionality to the Taskbar.
As the build went live, Insiders from all over the world started to download and install it. The feedback was already pouring in, and the team was eager to hear what users thought of the new build.
One of the Insiders, a tech enthusiast named Alex, was particularly excited to try out the new build. He had been waiting for weeks to see the updated UI and was eager to test out the new features. He downloaded the ISO file, burned it to a USB drive, and booted up his machine.
As he installed the build, Alex couldn't help but feel a sense of excitement. He had been using Windows 10 for years, but this new build felt fresh and exciting. He spent hours exploring the new features, testing out the updated Settings app, and marveling at the improved performance.
Meanwhile, back at Microsoft, the team was busy monitoring the feedback and fixing any issues that arose. They were thrilled to see that Insiders were enjoying the new build and were already reporting bugs and suggesting new features.
As the day went on, the team made a few more tweaks and adjustments, and by the evening, they were ready to release another build, 21391. But for now, Build 21390 was out in the wild, and the Insiders were loving it.
Technical Specifications:
Changes in Build 21390:
The Insider team couldn't wait to see what the community would do with this new build. Would they find any major bugs, or would they love it just as much as Alex did? Only time would tell.
Windows 10 Insider Preview Build 21390 was a milestone build released in May 2021 as part of the "Dev Channel" (formerly the Fast Ring) . This specific build is now considered and is no longer officially supported by Microsoft.
If you are looking for this specific build, please be aware that it will likely display an "expiration" notice and may refuse to boot or restart frequently after its hardcoded time-bomb date. 🛠️ How to Obtain Build 21390
Because Build 21390 is older, it is no longer the primary download on the Official Windows Insider ISO page
. To get it, you must use community-driven tools that fetch files from Microsoft's Update Servers (UUP). 1. Using UUP dump (Recommended) windows 10 insider preview build 21390 x86 x64 iso incl
This is the most reliable way to generate a custom ISO for specific older builds. Visit the site: Search for Build: in the search bar. Select Architecture: (64-bit) or Choose Edition: Select your desired edition (Home, Pro, etc.). Download & Build: Download the script package, extract it, and run the uup_download_windows.cmd
file. This script will download the necessary files from Microsoft and compile them into a single ISO. 2. Official Insider Site (For Current Builds) If you just want the Insider build, follow these steps: Sign in to the Windows Insider Program Navigate to the ISO Download
Select the "Dev Channel" or "Beta Channel" from the dropdown.
Note: Build 21390 is likely replaced by newer 22H2 or Windows 11 builds. ✨ Key Features of Build 21390
At its release, this build focused on visual refinements and system performance: New Fluent Icons: Updated iconography for the Task Manager MSI installers Windows Terminal:
This build allowed users to set Windows Terminal Preview as the default terminal emulator. News and Interests:
Fixed issues where taskbar text appeared blurry on certain resolutions. Dark Mode Fixes:
Resolved an issue where search text in File Explorer was black-on-black. ⚠️ Important Risks & Limitations Hands on with Windows 10 Insider Preview Build 21390
In the late spring of 2021, a unique chapter in the history of Windows was written with the release of Windows 10 Insider Preview Build 21390 . Released on May 26, 2021, to the Dev Channel
, this build sat at a crossroads—it was the final "true" Windows 10 Dev build before the world-changing unveiling of Windows 11 just weeks later. The Story of Build 21390: The Last of its Kind
Build 21390 was a quiet but significant milestone. It belonged to the
release branch, a codename that insiders would soon realize was the foundation for the next generation of Windows. While it looked like Windows 10, it was secretly paving the way for the "Sun Valley" visual overhaul. A Final Farewell to Live Tiles
: For many, this build is remembered as the last version of Windows to feature the Live Tiles
first introduced in Windows 8, before they were replaced by the static icons of the Windows 11 Start menu. A Pivot Point
: Just after its release, Microsoft began a series of "servicing pipeline" tests (Builds 21390.1000, 21390.1010, and 21390.2025) which contained no new features but were used to ensure the update system could handle the massive transition to Windows 11 coming that June. The 32-bit Sunset : This was also one of the last builds to offer full x86 (32-bit)
support, a legacy architecture that would be largely phased out in the Windows 11 era. Key Features and Changes
Though a "minor" update on the surface, Build 21390 included several refined touches: Announcing Windows 10 Insider Preview Build 21390
Windows 10 Insider Preview Build 21390 a historic release from the "Cobalt" development branch, first made available to the Dev Channel on May 26, 2021
. Often cited as the final "true" Windows 10 Insider build before the official unveiling of Windows 11, it served as a bridge between the classic Windows 10 interface and the modern design language. Windows Blog Key Features & Visual Updates
While build 21390 was a minor update, it introduced several polished visual elements that eventually became standard: New Fluent Icons: Updated iconography for Task Manager MSI Installers Terminal Integration: For the first time, users could set Windows Terminal Preview (v1.9+) as the default terminal emulator. Sun Valley Glimpse: It featured early previews of Windows 11 desktop icons Segoe UI Variable Final Appearance of Live Tiles:
This build marks the last appearance of the Windows 8-era Live Tiles before they were replaced by the Windows 11 Start menu. Microsoft Learn Critical Fixes & Known Issues The Changelog - Windows Insider Program - Microsoft Learn
Windows 10 Insider Preview Build 21390 was a notable release in the Dev Channel during the mid-2021 period, serving as one of the final builds in the "Cobalt" semester before the transition to Windows 11. It was primarily focused on visual refinements and testing the servicing pipeline rather than major new functional features. Key Features and Visual Changes
Iconography Improvements: The most visible change was the introduction of new Fluent Design icons for the Task Manager and MSI installers.
Default Terminal Emulator: This build allowed users to set Windows Terminal Preview (version 1.9+) as the default terminal emulator across the OS.
Final Appearance of Live Tiles: According to community observations, this build was one of the last to feature the Live Tiles introduced in Windows 8 before they were phased out in favor of the Windows 11-style Start menu. Many digital archivists have uploaded verified hashes of
Segoe UI Variable: It featured early previews of the Segoe UI Variable font and Windows 11-style desktop icons. Release History and Technical Details
Initial Release: Released to the Dev Channel on May 26, 2021.
Cumulative Updates: Microsoft released several servicing pipeline updates for this build to test deployment mechanisms, including: 21390.1000 (June 7, 2021) 21390.1010 (June 10, 2021)
21390.2025 (June 14, 2021) — The final version of this specific branch.
Architecture Support: This build was available for x86 (32-bit), x64 (64-bit), and ARM64 architectures. Announcing Windows 10 Insider Preview Build 21390
The Leaked Build
It was a typical Tuesday evening for Microsoft's Windows Insider team. The developers had just wrapped up a long day of coding, testing, and debugging. As they were about to leave for the day, one of the engineers, Alex, noticed something peculiar. A colleague, John, had left his laptop unattended on the conference room table. Curious, Alex glanced at the screen and saw that John had accidentally left a sensitive folder open. The folder was labeled "Windows 10 Insider Preview Build 21390 x86 x64 ISO incl".
Alex's eyes widened as he scanned the contents of the folder. He saw not only the ISO files for the 32-bit and 64-bit architectures but also a set of cryptic notes and a detailed changelog. Without thinking, Alex quickly downloaded the ISO files onto his own laptop, thinking he could take a look later.
The next day, Alex couldn't resist the temptation. He booted up his laptop and installed the new build, taking note of the improvements and changes. The new build, 21390, seemed incredibly stable, with noticeable performance enhancements and a refreshed UI.
The Online Leak
Meanwhile, an anonymous user, known only by their handle "TheVigilant", had been sniffing around Microsoft's internal networks. They had been monitoring the company's FTP servers and had caught wind of the new build. TheVigilant quickly grabbed the ISO files and began sharing them on a popular tech forum.
The thread, titled "Windows 10 Insider Preview Build 21390 x86 x64 ISO incl", quickly gained traction. Users were excited to try out the latest build, and TheVigilant's post attracted hundreds of comments, with many more downloading the ISO files.
Microsoft's Scramble
Back at Microsoft, the Windows Insider team was oblivious to the leak. That was until they received a flood of complaints and queries from users who had downloaded the build. The team quickly realized what had happened and sprang into action.
The program manager, Rachel, immediately contacted the company's security team to assess the situation. They quickly verified that the leak was legitimate and contained sensitive information. Rachel and her team worked over the weekend to contain the damage, updating their internal systems and re-issuing new, non-leaked builds to Insiders.
The Fallout
The leak of Build 21390 caused a significant stir within the Windows Insider community. Some users were thrilled to have access to the latest build, while others expressed concern about the potential security risks.
Microsoft took steps to address the situation, publishing a statement on their blog about the incident. The company reassured users that they were taking steps to prevent similar leaks in the future and thanked TheVigilant for their contribution to the Windows Insider program.
Alex, the engineer who had initially downloaded the build, received a gentle reprimand from his supervisor. John, whose laptop had been left unattended, received a friendly reminder about the importance of securing sensitive information.
TheVigilant, the anonymous user, remained at large, their identity still unknown to Microsoft. However, they had already begun to participate in the Windows Insider program, providing valuable feedback and helping shape the future of Windows 10.
The story of Build 21390 became a cautionary tale within Microsoft, highlighting the delicate balance between collaboration, transparency, and security. As the company continued to develop and refine Windows 10, the Insider program remained a vital component, driving innovation and fueling the passion of Windows enthusiasts worldwide.
You're looking for information on a specific Windows 10 Insider Preview build!
The build number you provided, 21390, is a part of the Windows 10 Insider Preview series. Here's what I found:
Build 21390: Released on June 17, 2021
This build is a part of the rs_prerelease branch, which is a pre-release branch for Windows 10. For users who despise Windows 11’s centered taskbar
Key Features and Changes:
Here are some of the notable changes and features in Build 21390:
Known Issues:
As with any Insider Preview build, there are known issues that Microsoft is working to resolve. Some of the known issues in Build 21390 include:
Downloading the ISO:
If you're looking to download the ISO file for Build 21390, you can try the following:
System Requirements:
To install Build 21390, your system should meet the following requirements:
Keep in mind that Insider Preview builds are pre-release software and may not be suitable for production environments or daily use. It's recommended to install this build on a virtual machine or a secondary device to test and provide feedback to Microsoft.
Windows 10 Insider Preview Build 21390 (CO_RELEASE) was released on May 26, 2021, and is notable for being the final Insider Preview build to feature the traditional Windows 10 user interface before the shift to Windows 11.
⚠️ Warning: This build expired on October 31, 2021. Expired builds will frequently reboot, show "evaluation copy" watermarks, and eventually refuse to boot entirely. Key Features & Changes
New Iconography: Updated Fluent icons for Task Manager and MSI installers.
Windows Terminal: Support for setting Windows Terminal Preview (v1.9+) as the default emulator.
Live Tiles: This build marks the final appearance of the Live Tiles introduced in Windows 8.
Bug Fixes: Resolved issues with blurry taskbar text, svchost.exe crashes, and dark mode text visibility in File Explorer. ISO Availability & Architecture
While Microsoft does not officially offer downloads for expired builds, they are often archived by third parties: Announcing Windows 10 Insider Preview Build 21390
Windows 10 Insider Preview Build 21390 was a significant release for the Dev Channel in May 2021. Often referred to as the "Cobalt" release (co_release), this build is highly regarded among enthusiasts as the "final" true Windows 10 Insider build before Microsoft shifted focus to Windows 11. Key Features and Iconography Changes
While this build did not introduce sweeping functional overhauls, it focused on refining the "Sun Valley" visual aesthetic that eventually defined the Windows 11 era.
Fluent Iconography: The Task Manager and MSI installer files received new Fluent-inspired icons.
Windows Terminal Integration: Users could finally set Windows Terminal Preview (version 1.9 or higher) as the default terminal emulator on Windows.
Refined Start Menu: Microsoft re-enabled a feature where folders in the Start menu containing only one item would display that item directly rather than the folder icon. Official Release and Servicing History
Build 21390 underwent several cumulative updates as Microsoft tested its servicing pipeline, which resulted in multiple sub-versions: Initial Build (21390.1): Released May 26, 2021. KB5004071 (Build 21390.1000): Released June 7, 2021. KB5004092 (Build 21390.1010): Released June 10, 2021.
KB5004123 (Build 21390.2025): Released June 14, 2021, the final iteration. Availability: x86, x64, and ISO Details Announcing Windows 10 Insider Preview Build 21390
Get-FileHash -Algorithm SHA1 C:\Downloads\21390.iso
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