Installing Windows: clean install, upgrade, and the unattended middle

Why this matters

Installing Windows is the most common irreversible thing a support technician does, and the questions about it are almost all about consequences rather than clicks. What survives? What is lost? What can be undone?

There is also a genuine professional point buried in this objective. The easiest way to make a difficult machine work is to reinstall it, and that is frequently the wrong answer — it costs the user their settings and their time, it destroys the evidence that would have explained the fault, and it fixes the symptom without ever identifying the cause. Knowing the options between "try one more thing" and "start again" is most of what separates a technician from someone who reinstalls.

The lesson

Clean install against in-place upgrade, and what each keeps

The two routes differ in exactly one dimension — what they keep — and everything else follows from that.

In-place upgrade. Setup runs from inside the running system. It keeps files, applications, and most settings. It is the right answer when the machine works and you are moving it to a newer version.

Clean install. Setup runs from media, the target partition is formatted, and the result is a new machine. It keeps nothing. It is the right answer when the existing installation is the problem, when moving between architectures, or when the machine is changing hands.

The in-between options, which are what the exam is usually poking at:

• Keep personal files only. Files survive, applications do not, settings do not. Useful when the profile is fine and the software is not.
• Keep nothing. Equivalent to a clean install performed from inside the running system.
• Reset this PC. The same two options presented as a recovery feature, with the additional choice of pulling a fresh copy from the internet rather than using the local recovery image.

Two facts worth carrying into a scenario question. Nothing in this list touches other partitions or other disks — a separate data drive survives all of them. And an upgrade leaves a rollback window, typically ten days, after which the previous installation is deleted and the option disappears. A user who is going to be unhappy will usually be unhappy within those ten days, which is precisely why the window exists.

Repair install: the option most technicians forget exists

There is an option between "reinstall everything" and "live with it", and it is the one technicians most often forget: running setup from installation media and choosing to keep files and applications.

This is the repair install. It replaces every system file, reregisters components, and rebuilds the store of system files — while leaving the user's applications, data and most settings in place. It is the correct answer for a surprising range of faults:

• Windows Update failing repeatedly with component-store errors.
• System file checker reporting corruption it cannot repair.
• A machine that starts but has multiple unrelated, unexplained faults.
• Features that vanish and do not return after the obvious repairs.

It takes about as long as an upgrade, it is far cheaper than a rebuild, and it requires media matching the installed version or newer.

The caveats are honest ones: it will not fix a fault caused by a third-party application or a driver, because it leaves both in place; and it is not a remedy for a compromised machine, because it leaves everything the intruder installed in place too. For the first case the answer is to remove the application; for the second the answer is a clean install, and that distinction comes back in the security objectives.

Drivers at install time, and the storage driver that stops setup dead

Modern installation media carries drivers for most common hardware, so this is a smaller problem than it was — with one very large exception.

If setup cannot see any disk, the storage controller driver is missing. This is the classic symptom: the installer runs, reaches the disk selection screen, and lists nothing. It happens most often with machines using a vendor-specific storage mode, and it has two fixes:

• Load the driver. The installer offers a "Load driver" button on that screen. The driver comes from the machine vendor's support site, on a second USB stick.
• Change the firmware setting. Many machines default to a proprietary RAID mode that setup does not recognise; switching the controller to AHCI makes the disk appear. This changes how the installed system addresses the disk, so it is a decision to make before installing, not after.

Beyond storage, the ordinary approach is: install with the drivers the media has, then install the vendor's drivers for chipset, graphics, and network — in that order, because the chipset driver often improves what the others can see. Windows Update supplies many of these automatically now, which is fine for general use and sometimes not enough for graphics or specialist hardware.

The professional habit worth building: before wiping a machine, note what hardware it has and check that drivers exist for the version you are installing onto it. A laptop whose wireless card has no driver for the new version is a laptop that cannot download its own driver.

Account creation, local against Microsoft account, and what each implies

Setup asks who will use the machine, and the answer has more consequences than it appears to.

A local account exists only on this machine. It is simple, it works offline, and it has no recovery path — if the password is lost, the password is lost, and the only routes back in are destructive.

A Microsoft account is a cloud identity. It brings password recovery, it syncs some settings between machines, it is required for some store and subscription features, and — the examinable part — it enables BitLocker recovery key escrow, so a device-encrypted machine can be recovered by the account owner rather than not at all.

A domain account replaces both in a managed estate and is joined after installation rather than during it.

What to tell a user, in a sentence each: a Microsoft account means you can get back in if you forget your password and your encryption key is saved where you can find it; a local account means the machine is entirely yours and entirely your responsibility.

One genuine trap. On a machine with device encryption active and a local account, the recovery key may exist nowhere but on that machine. A firmware update or a hardware change can then leave the user facing a recovery prompt with no key and no route to one. Checking where the recovery key is stored is a two-minute job that has saved entire machines.

Unattended installation and imaging, described honestly for one machine

Unattended installation answers setup's questions from a file instead of from a person, and imaging skips the questions entirely by copying a finished machine.

Honestly described for one machine: you probably do not need either. An answer file takes longer to write correctly than an interactive install takes to sit through, and a captured image is only worth making when you are going to apply it more than a handful of times. Reaching for them on a single machine is a common beginner instinct and it is usually the slower path.

Where they genuinely pay:

• More than about five identical machines. The arithmetic turns over quickly.
• Machines that will be rebuilt repeatedly — a training room, a test bench, a kiosk.
• Estates where the build must be provably identical, because "it works on mine" is not an answer anyone can act on.

What a support technician should be able to do is narrower and more useful than building the pipeline: recognise that a machine is imaged, ask whether the fault is present on a freshly imaged machine, and know that fixing it in the image fixes it everywhere while fixing it on one machine fixes it once.

The one component worth naming is sysprep, which strips a machine of its identity — its computer name, its security identifier, its activation state — so an image made from it can be applied to other machines. An image captured without it produces duplicates that misbehave on a domain in ways that are hard to diagnose, and "was it sysprepped?" is a good early question.