A PC that takes a minute to open a folder, with Task Manager showing the disk pinned at 100 percent, is usually not a broken disk. It is one process using all of it, and the same screen that shows the number will name the process if you sort by the right column.
First: name the process
Press Ctrl, Shift and Esc together to open Task Manager. Microsoft documents this in its page on improving PC performance in Windows, which points at the Performance and Startup apps tabs for exactly this.
On the Processes tab, click the Disk column header to sort by it. The top row is your answer. Everything below is noise until you have dealt with the top row.
Second: the three that account for most of it
Windows Update is the most common, and the most misread. A PC downloading and installing an update will hold the disk for a long stretch, and killing it only delays the same work to the next restart. If the top process is a Windows Update service, the fix is to let it finish.
Search indexing is second. After a big update, or after you copy a large folder in, Windows rebuilds its index and that is disk-bound by nature. It settles on its own, usually within a day.
Antivirus scanning is third, and includes Windows Security itself. A scheduled full scan looks exactly like a fault while it runs.
All three share a property worth knowing: they end. A disk at 100 percent for twenty minutes after a restart is ordinary. A disk at 100 percent all day is not.
Third: free space, because a full drive is slow
A drive with almost nothing free will behave badly regardless of what is running. Microsoft's path is Start, then Settings, then System, then Storage, then Cleanup recommendations, which groups temporary files, large or unused files, files synced to the cloud, and unused apps.
Microsoft also keeps a page on freeing up drive space with the rest of the options.
Fourth: what starts with the machine
If the disk is busy from the moment you log in, the cause is something starting with Windows. Task Manager has a Startup apps tab that lists them with a startup impact rating, which Microsoft documents on its page about configuring startup applications.
Disabling something there does not uninstall it. The app still runs when you open it; it just stops running before you asked.
When it is the drive itself
One pattern points at hardware rather than software: a mechanical hard drive, as opposed to an SSD, in a PC running a current version of Windows. Modern Windows assumes an SSD in several places, and a spinning drive can sit at 100 percent doing work an SSD would absorb without showing it. In that case nothing in Task Manager is wrong and no setting fixes it.
Microsoft also documents a narrower case where disk usage reaches 100 percent after resuming from sleep, which is worth knowing if the timing matches.
If the disk turns out to be fine and the machine is still slow, the question moves to whether the PC is getting what current Windows expects of it. What a Copilot+ PC has that yours might not covers where that line sits today, and what it actually gates.
Last updated October 4, 2026