It is currently not possible to buy a new x86 processor that runs below 1 GHz. Most mainstream desktop CPUs are well over 2 GHz or even in the 3 GHz range and have much higher base clocks. However, in the 1980s and 1990s, processors running at just a few MHz were common, and the original IBM PC itself ran at just 4.77 MHz.
Can you run a modern Windows operating system on a CPU with such a slow clock speed? Developer and popular YouTuber NTDEV proved that Windows 7, released in 2009, could be booted and used on a Pentium-S processor downclocked to just 5 MHz. That’s a full 995 MHz below his 2009 OS minimum requirement of 1 GHz. On our test system he only had 128MB of RAM, which is well below Windows 7’s minimum requirement of 1GB.
In the YouTube video (embedded below) NTDEV shows the system. This is actually running in a virtual machine. 86Box emulator (opens in new tab), boot Windows 7 Ultimate, launch a program that shows a clock speed of 5.00 MHz, and run Notepad. By the way, if you follow the accelerated time counter in the video, you’ll see that it took over 28 minutes before the Windows 7 desktop appeared.
In this video you can see NTDEV powering a virtual machine POSTing as a Pentium-S running at 50 MHz with 128MB of RAM. However, by the time Windows 7 is running, it’s somehow downclocked to 5 MHz.
NTDEV will boot the system and give you the option to use normal mode or safe mode. They choose normal mode, but probably due to changes the developer made to the installation, the bootloader shows a list of system files while loading, and the final desktop shows a “safe mode” watermark. so Windows 7 appears to boot into safe mode. That.
NTDEV doesn’t give out many details about what they did to get Windows 7 running on such a slow system. However, the explanation they wrote for the YouTube video is, “After so many optimizations, including disabling LogonUI and transitioning to his dysfunctional OOBE state, we finally managed to get Windows running at just 5MHz. I was able to run 7” gives a clue.
Combining DLL files, system services, and other components from any version of Windows can certainly reduce the required system resources. Of course, we’ve given up a lot of functionality, not just the logon interface, but perhaps most of the graphical elements.
The desktop displayed by NTDEV in the video is[スタート]Note that there are no menus, no wallpapers, and even the windows themselves have very simple themes. There is no way Aero transparency works here. To start the program, WCPUID / Real Time Clock Checker, NTDEV, you need to enter its shortcut name at the command prompt. Do the same later to launch Notepad.
Perhaps the most impressive thing about this entire video is that NTDEV can at one point run four different programs: Command Prompt, WCPUID, Winver (showing the Windows 7 version), and Notepad with text. So this is a fairly stable boot.
From their tweets and comments, it’s clear that NTDEV hasn’t given up on its quest to make Windows 7 run even slower. Perhaps in the near future it will even go down to 4 MHz.
