Although the system needs 28 minutes to boot up, it can do multiple tasks concurrently.
Currently, it is impossible to find an x86 processor with a base clock lower than 1 GHz on the market; most modern desktop CPUs have base clocks that are more than 2 GHz, and some even reach 3GHz, while they can also be boosted to go higher.
Nevertheless, in the 80s and 90s, processors that ran at a low MHz were widespread, with the first IBM PC even having a speed of scarcely 4.77MHz.
Is it possible to run a contemporary Windows OS on a processor with such a slow speed?
The developer and YouTuber NTDEV have shown that it is possible to boot and use Windows 7 (launched in 2009) on an underclocked Pentium-S processor at 5 MHz.
That’s 995 MHz lower than the 2009-era OS’s minimum requirement of 1 GHz, and it only had 128MB of RAM, significantly below the 1GB needed to run Windows 7.
In the YouTube video below, NTDEV demonstrates a virtual machine in the 86Box emulator which boots up into Windows 7.
Finally, launch a program that reveals its 5.00 MHz clock speed and demonstrates how to open Notepad. Moreover, it takes a long time in the video, actually 28 minutes for the Windows 7 desktop to appear if you follow the sped-up time frame!
In the video, NTDEV can be seen powering on a virtual machine that displays a POST as a 50MHz Pentium-S processor with 128MB of RAM.
Even though NTDEV was able to decrease the clock speed to 5 MHz by modifying 86Box’s source code, it is still considered a low speed.
NTDEV is given the option of using either Normal or Safe mode when booting the system, and he chooses Normal, but it instead loads up into Safe mode, displaying all of the.sys ,.dll, and .exe files as they boot up.
According to NTDEV, as part of their hacking process, they edited the BCD (boot configuration data) so that even if you choose Normal mode, Safe mode will still boot.
Windows 7 Functioning With Slow CPU
NTDEV revealed that in order to get Windows 7 functioning with a slow CPU, he had to reduce many system resources by running Safe mode and disabling almost all drivers and services so only three were active at start-up.
Additionally, he needed to take care of a problem with logonUI.
Frequency Below 50MHZ
NTDEV informed us, “When the frequency goes below 50MHz, the login screen (logonUI) does not appear.
Therefore, in order to reach a command prompt I had to set up a pseudo-OOBE state by modifying the registry and deleting all contents in the c:\windows\system32\oobe folder so that it wouldn’t boot.”
A Developer Was Able to Run Windows 7 on a 5 Mhz CPU With 128MB of Ram.
Out of Box Experience
The OOBE (out-of-the-box experience) is what you get when you’re running a Windows installer. It doesn’t have a Start menu or Windows Explorer.
During OOBE, you can typically get the command prompt by pressing Shift + F10, though it may still not be available.
We noticed that the desktop NTDEV in the video doesn’t have a Start menu, there’s no wallpaper and the windows themselves have a very basic theme; hence, no Aero transparencies will be available.
To launch WCPUID / Real Time Clock Checker, NTDEV has to type its shortcut title into the command prompt. Later, he does the same to initiate Notepad.
What makes this particular video extraordinary is NTDEV’s ability to run four different programs concurrently – the command prompt, WCPUID, Winver (demonstrating the Windows 7 version), and Notepad with text inside – in a relatively stable setting.
NTDEV informed us that he has experimented with Windows 7 running on a clock speed of as low as 3 MHz, however, it was not functional enough to create a noteworthy video.
He commented that in the past, he’s managed to run Windows 7 on a machine with only 36MB of RAM, but chose to use 128MB so that the sample system wouldn’t require virtual memory. During his demo, the computer in question consumed around 70MB of RAM.
Storage Virtual Machine Takes
The virtual machine takes up less storage space than the 16GB that is needed for Windows 7.
NTDEV noted that the entire installation requires less than 1GB of space on the system, and the .wim file disk image for the OS is smaller than 350MB.
NTDEV, who has already accomplished the feat of running Windows XP with a processor speed of only 1 MHz (opens in new tab), is now trying to get Windows 10 or 11 to run at 3 MHz or up to 5 MHz on a slower than 1 GHz processor.
He noted that the 5MHz Windows 7 system, which takes over 28 minutes to boot up, is far from the slowest machine he’s used.
He joked, “Compared to Windows XP on 1 MHz, this is nothing! That thing took 3 hours just to turn on!”
What do you think? Tell us in the comments section below.