What Is Windows Sandbox and Its Vanishing Disk Image

A full VM you never install

The feature ships as an optional component: turn on Windows Sandbox in the Windows Features dialog (optionalfeatures.exe) or with a single DISM command, and a Start-menu entry appears. The requirements are modest but firm: Windows Pro or Enterprise, virtualization enabled in the firmware, at least 4 GB of RAM with two cores, and a gigabyte or two of free disk for the working files.

What you get is a clean, unactivated Windows in a window, with networking, clipboard sharing and copy-paste working out of the box. Under the hood it is a real lightweight VM running on the Hyper-V hypervisor — not a container, not a remote session — just one that pretends nothing happened when you close it.

Where the disk image goes — and why it vanishes

At launch, the sandbox mounts a pristine system image read-only and builds a temporary write-on-top layer — a disposable VHDX — for everything you do inside. At shutdown that layer is destroyed by design, which is why the machine you were just using has evaporated, files and all.

• The base image is a clean Windows snapshot; the sandbox never sees your installed apps or your files
• Everything you do inside lands in a temporary VHDX that exists only while the sandbox runs
• On close, the whole layer is discarded: no files, no registry changes, no installed programs survive
• Clipboard copy-out and mapped folders are the only legitimate ways to keep something
• After a crash or power loss, leftover working files in temp folders are safe to delete once the sandbox is closed
• Don't move real work there: a sandbox session is the wrong home for anything you want tomorrow

When to use it, and when a real VM is better

The sweet spot is short, suspicious work: opening that sketchy installer, testing a download that promises too much, checking a link you'd rather not feed your main browser. A session costs you a minute, and the blast radius is zero. A .wsb config file can lock it down further — disable networking, turn off the virtual GPU, map one folder read-only — which is the right posture for genuinely hostile files.

What it is not is a second PC. There is no snapshot you keep, no state between runs, no way to install your toolkit once and reuse it — for that, a full VM (or WSL for Linux work) is the honest answer. If you need to keep what you test, keep it in a VM; if you need to be sure it's gone, that's the sandbox's whole job.

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