Disk Cleanup: The Second Button Most People Miss

You ran Disk Cleanup, it offered you a couple of hundred megabytes, and you closed the window disappointed. There is a second button on it that changes the number entirely.

The first list is the small one. It is not the whole tool, and the bigger half is one click away.

I measured what was actually sitting on this machine before writing, and the biggest pile was not the one people empty first.

Opening it, and what the first list covers

Thirty seconds of orientation.

Documented by Microsoft on its Disk Cleanup page: "In the search box on the taskbar, type disk cleanup, then select it from the results."

⭐ Microsoft names what it ticks for you by default: "Downloaded Program Files, Temporary Internet Files, and Thumbnails."

⚡ Those three are small. A few hundred megabytes on a typical machine, which is why the first screen underwhelms.

⚠️ `cleanmgr` in the Run box opens the same thing if you would rather type it.

The second button, and why the number jumps

The point of the whole page.

Microsoft describes it plainly: choose Clean up system files, "select a drive, select OK", and when it has finished calculating you can "select the type of system files you want to delete."

⭐ That is a different, longer list. Windows Update cleanup, delivery optimization files, previous installations, error reports and old device driver packages all appear only after that click.

⛔ It needs administrator approval, which is why it is a separate button rather than part of the first list.

⚡ The gigabytes live on that second list. The first screen is the appetizer.

Ours: what was actually sitting here

The measurement, and the surprise is which pile was biggest.

Ours, and totalled on this PC before writing. The user temporary folder held 11,622 files and about 1.9 GB. The Windows Update download cache held 209 MB.

⛔ The Recycle Bin held twelve files and effectively nothing. That is the one everybody empties first. Here it was the smallest thing on the list by a wide margin.

⚡ Run the same total on your own machine. Nothing is deleted:

Get-ChildItem $env:TEMP -Recurse -File -Force -ErrorAction SilentlyContinue |
  Measure-Object Length -Sum

⚠️ Only counts and sizes were read here, not file names. The number is the useful part.

The one item to think about before ticking

The irreversible one, and Microsoft warns about it directly.

In Microsoft's words, if it is "fewer than 10 days since you upgraded to Windows, your previous version of Windows will be listed as a system file you can delete", and doing so removes "your Windows.old folder, which contains files that give you the option to go back to your previous version of Windows."

And the warning itself: "If you delete your previous version of Windows, this can't be undone."

⭐ Ours, and checked here: no Windows.old folder exists on this machine, so nothing was at stake. On a recently upgraded PC it can be twenty gigabytes or more.

⛔ That is the trade. Real space back, and no way to roll the upgrade back afterwards.

⚠️ After ten days Windows removes it anyway. Waiting costs you nothing if you are unsure.

What is safe to tick

The rest of the list, in plain terms.

⭐ Temporary files, thumbnails and delivery optimization files all regenerate. Nothing is lost.

⭐ Windows Update cleanup removes superseded update files. It can be large. And it is safe once your machine is running normally.

⚠️ Downloads is on the list on some builds, and it is not a cleanup item. That is your own downloads folder, and ticking it deletes whatever is in it.

⛔ Ours, and marked as ours: read the description under each item before ticking. The dialog explains every one. Almost nobody scrolls it.

What Storage Sense does instead

Because the two tools overlap and one of them keeps working.

⭐ Storage Sense runs on its own and handles the temporary side automatically. Disk Cleanup only runs when you open it.

⚡ So use Disk Cleanup once, for the system files list, and leave Storage Sense on for the rest.

⚠️ If the drive is genuinely full rather than untidy, there is a proper order for finding the space and none of it starts here.

Where the space usually is instead

Being honest, because cleanup rarely solves a full drive.

⛔ Installed programs and personal files are almost always the bulk. Cleanup tools cannot touch either.

⚠️ And a drive that fills again next month has something writing to it. That is a different investigation.

⭐ Ours: check what kind of drive you have before running anything else on it. The right maintenance differs and the wrong one wastes an evening.

Status: read against Microsoft's Disk Cleanup page 25 August 2026, on Windows 11. Microsoft supplies the route, the three items ticked by default, the description of the Clean up system files button, the ten day window on a previous Windows installation, and the warning that deleting it cannot be undone. The temporary folder, update cache and recycle bin totals were measured on this PC.

How do I open Disk Cleanup in Windows?

Type disk cleanup into the search box on the taskbar and select it, which is Microsoft's own route. Typing cleanmgr into the Run box opens exactly the same tool if you prefer the keyboard.

Why does Disk Cleanup only find a few hundred megabytes?

Because the first screen ticks only three small categories. Press Clean up system files. Windows then recalculates against a much longer list, which is where update cleanup and previous installations appear.

Is it safe to delete previous Windows installations?

It frees real space and it cannot be undone. Microsoft warns that deleting Windows.old removes your ability to go back to the previous version. If you are unsure, wait, because Windows removes it automatically after ten days anyway.

Should I use Disk Cleanup or Storage Sense?

Both, for different jobs. Storage Sense runs by itself and handles temporary files continuously. Disk Cleanup is worth opening occasionally for the system files list. Storage Sense does not cover that.

The Short Version

• Microsoft ticks only three small categories on the first screen by default.
• Clean up system files is a second button that recalculates against a much longer list.
• That second list is where update cleanup and previous installations appear.
• The temporary folder here held 11,622 files and about 1.9 GB.
• The Recycle Bin held twelve files and effectively nothing, and it is the one people empty first.
• Deleting a previous Windows installation cannot be undone, and Microsoft says so.
• Windows removes it automatically after ten days, so waiting costs nothing.
• Storage Sense keeps working afterwards. Disk Cleanup only runs when you open it.

Where to Next

Open Disk Cleanup and press Clean up system files straight away. The first screen is not the tool, and the second one is where the space is.

Read the description under each item before ticking it. The dialog explains all of them and almost nobody scrolls that panel.

Then total your own temporary folder with the line above. Seeing the real number makes the decision obvious rather than a guess.

Should Clean up system files offer you something unusually large, tell me which item in the comments. Those vary a lot by how the PC has been used.