Fix Windows 100% Disk Usage in Task Manager (Slow PC)

Updated: 11/29/2025

Your computer is running incredibly slow. You open Task Manager, and the 'Disk' column is a solid red 100%, even though you aren't downloading anything. This is a classic Windows bug where background optimization services get stuck in a loop, constantly reading/writing to your hard drive and paralyzing your system.

Table of Contents

Method 1: Disable SysMain (Superfetch)

SysMain tries to preload apps you use often into RAM. On older HDDs or some SSDs, this causes constant grinding.

Step 1: Open CMD

Search for cmd in the Start Menu, right-click, and Run as Administrator.

Step 2: Stop Service

Type this command and hit Enter:

net.exe stop sysmain

If the Disk usage drops to 10% instantly, this was the culprit. You can permanently disable it in services.msc.

Method 2: Reset Virtual Memory

If your RAM is full, Windows uses your drive as 'fake RAM' (Pagefile). If the file size is wrong, it loops.

  • Press Win + Pause/Break (or search 'Advanced System Settings').
  • Go to Advanced > Performance Settings > Advanced.
  • Click Change under Virtual Memory.
  • Uncheck 'Automatically manage'. Set a custom size (e.g., 8000MB min and max). Click Set and Restart.

Method 3: Disable Windows Search Indexing

Windows constantly scans your files to make them searchable. If it gets stuck on a corrupted file, it hits 100%.

Open Admin Command Prompt again and type:

net.exe stop "Windows Search"

Check Task Manager. If usage drops, consider keeping this disabled or rebuilding your search index overnight.