I want my PC to run slow. I am going on vacation and I have little kids at home that I know prefer to use my PC instead of their own. (I have one account that is not password protected.) I don't intend to add a password or anything like that, I want my computer to run slow so that they feel like they have a better PC and use their own instead. (They are not my kids and I am actually curious how to do it.)

I know slow is a broad term but I intend it as you wish, whether is by limiting the CPU usage, RAM...

After a bit of research I found a program called CPUKiller but the free version only allows for 20 minute sessions and that is not enough for me.

I am not discussing if this is the best approach or not; I just want to know if it's possible. I am using Windows 10, 64 bit, 4GB DDR3 RAM.

Question is:

Is there an good (free) alternative to CPUKiller? If not, is there a better way of doing what I intend?

  • 1
    From the description it seems that CPU killer is consuming much CPU, so the PC might be slow but have high energy cost and fans may spin up. Commented Jul 6, 2016 at 17:54
  • 2
    Using CPU killer and keeping computer busy has its own overhead than temporarily setting a password for the account. Later you can remove it when you are back.
    – atp9
    Commented Jul 6, 2016 at 17:57
  • 5
    The old joke is that if you want it to run slow, just install Windows. ;-) Commented Jul 6, 2016 at 18:33
  • 1
    this is actually nice IMO, and something ive never thought of. sort of a blacklist if you will. ill have a go at this too when im out and about
    – FONZ
    Commented Jul 8, 2016 at 8:20
  • 1
    You could also make it really slow to login to the account without a password, but fast to your account.
    – gcampbell
    Commented Jul 8, 2016 at 14:02

4 Answers 4


You can use msconfig, which is a built-in utility of Windows, and turn off CPUs:

  1. Go to the tab "Boot"
  2. Select your boot configuration (on normal user's PCs, there's only one)
  3. Click "Advanced options"
  4. Check "Number of processors"
  5. Select 1
  6. Check "Maximum memory"
  7. Enter 2048 (or a value which you get by experimenting)

Do not use any of the debug settings, since you might be unable to boot the PC because it's waiting for a developer connection.

In addition, you can go to the Control Panel and change the maximum CPU usage:

  1. Power Options
  2. Change plan settings
  3. Change advanced power settings
  4. Processor power management
  5. Maximum processor state
  6. On battery: 50% (or a value that you get from experimenting)
  7. Plugged in: 50% (or a value that you get from experimenting)
  • Thanks, will also be trying out this method, i'll report back. Commented Jul 7, 2016 at 8:21
  • 1
    really nice and works just fine
    – FONZ
    Commented Jul 8, 2016 at 8:22

If your BIOS allows it, forget all these programming solutions.

Goto into the BIOS and down clock your CPU, and it will really be slower.

  • Nice response, my pc per say doesn't allow it but it might save someone in the same situation as me. Commented Jul 7, 2016 at 8:20

I made a simple python 3 script to do just that.

import multiprocessing
import hashlib

power = 1000

Power guide:
1  - CPU usually at 100%, pretty laggy but usable
2  - Web browser starts to lag a lot
5  - Switching between programs starts being a bit laggy
10 - Some program freezes almost every 10 seeconds
50 - Can't even type in notepad while this programis running
1000 - Renders the computer useless

def worker():
    x = 1
    while True:
        x += 1

if __name__ == '__main__':
    print("Stressing CPU at power: " + str(power))
    jobs = []
    for i in range(multiprocessing.cpu_count()*power):
        p = multiprocessing.Process(target=worker)

It has a neat power option that allows you to control the slowness.

How to make it run correctly:

  1. Download and install Python 3 (During installation check "Add Python to PATH")
  2. Copy and paste the above script to a file with a .pyw extension.
  3. Move the file to C:\Users\USERNAME\AppData\Microsoft\Windows\Start Menu\Programs\Startup to make it run when the user logs on. (Replace USERNAME with the username of the user you want to lag)

Note: The power scale was approximated on a dual-core computer.

  • Thanks! i have python on my machine going to try that later, will report back as soon as i am done testing. Commented Jul 7, 2016 at 8:19
  • it works thanks, one of the best answers but i have to mark the above as it requires less setting up hassle. I loved your code! Commented Jul 8, 2016 at 15:50

I know this is an old question, however for people finding it now... if you cannot down clock your PC and are considering to use an application to keep the CPU busy, consider running:

In fact, SETI@home uses the BOINC software, which host other similar projects.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.