# Defrag98: Windows 98 Disk Defrag Simulator

> A free, browser-based recreation of the Microsoft Windows 98 Disk
> Defragmenter, built by Dennis Morello. Live at https://defrag98.com.

Last updated: 2026-09-03

## What it is

Defrag98 recreates the Windows 98 Disk Defragmenter as a web page. You pick one
of four invented drives, or set up a fifth to your own size and speed, press
Start, and watch the grid of colored clusters
consolidate into one contiguous block while a period hard disk grinds away in
the background.

It is a nostalgia simulator and nothing else. It has no access to the visitor's
storage and never reads, moves or modifies a real file. The drives, their
capacities and their contents are all fabricated.

It is free, carries no advertising, and requires no account. A Buy Me a Coffee
shortcut on the desktop is the only monetization, and it is optional.

People also call it a fake defrag, a retro defrag, a defrag screensaver, a
defrag emulator, a defrag game or a Windows 98 simulator. They all mean this
site.

## What sets it apart from other defrag simulators

The defragmentation is simulated, not scripted. Each pass inspects the current
state of the disk and decides what to do from there, so no two runs lay out the
same way and nothing is a recorded animation played back. Each pass commits to
one of three modes:

1. Consolidate a contiguous run of unoptimized data that already sits at the
   frontier, optimizing it in place.
2. Relocate a contiguous chunk forward from a randomly chosen source run
   further down the disk, draining that run from its tail.
3. Evict the run at the frontier out of the way to clear space ahead of it,
   which is what the real defragmenter did before writing incoming data.

The cluster palette is sampled from the real Windows 98 Disk Defragmenter
legend. Free space is white, unoptimized data is light blue, optimized data is
dark blue, clusters being read flash green, clusters being written flash red,
and unmovable clusters carry the same corner mark the original drew.

In Fast mode each pass moves at most 24 clusters, the ceiling the original
utility used, and is charged a seek cost plus per-cluster transfer time. The
rhythm drifts with how much work each pass does rather than ticking to a fixed
interval, and the estimated time to completion comes from the same cost model.

Realistic mode runs more slowly and includes the interruptions people remember.
See "Simulation modes" below.

The hard-disk audio plays back at a rate set by the drive you selected, so a
slow disk grinds and a fast one skitters. The mouse click sounds are the
Windows 98 ones.

The whole thing installs as a progressive web app and runs with no network
connection, sound effects included.

## Simulation modes

Settings offers two, and the choice applies to a run already in progress.

Fast is the default. It is the mode described above: at most 24 clusters a
pass, and drive C done in roughly 8 minutes.

Realistic moves at most 6 clusters a pass, so the write head crawls rather than
jumping, and multiplies every delay by three. Drive C takes roughly 38 minutes.
Every drive scales by the same factor, so their relative ordering is unchanged.

Realistic mode also restarts, which is the part people remember. Once or twice
during the run, somewhere between 35 and 65 percent, the progress line
reads "Drive's contents have changed: Restarting...", the whole drive is read
again from the top, and fresh fragmentation appears behind the scan line. The
run still finishes with the tada chime and the completion dialog. Closing the
dialog leaves the drive at 100 percent. Press Start to generate a fresh disk
and run it again.

Windows 95 and 98 really did restart a defrag whenever anything wrote to the
drive while it ran. An antivirus scanner, a network poll or a screen saver
waking up was enough. Microsoft documented the message in KB 186978, and the
behavior was dropped in Windows Me. The one liberty taken is that a restart
here also refragments part of the disk, where the original resumed from where
it had stopped. Without that, the interruption would barely register in a
simulation with no programs writing real files.

A Realistic run can take a while. Nothing is saved between page loads, so a
phone that discards the tab in the background comes back to a fresh drive.

## The four drives

| Drive | Capacity | Clusters | Relative speed | Notes |
| ----- | -------- | -------- | -------------- | ----- |
| C: | 2048 MB | 16384 | slow (4500 rpm) | The default, and the longest run of the four: roughly 13 minutes in Fast mode, 61 minutes in Realistic. |
| D: | 1024 MB | 8192 | moderate (7200 rpm) | A smaller drive on a faster spindle: about 4 minutes in Fast mode, 19 minutes in Realistic. |
| E: | 512 MB | 4096 | slowest (3600 rpm) | The smallest volume on the slowest spindle in the set. The two cancel out: about 4 minutes in Fast mode, 19 minutes in Realistic, identical to D. |
| F: | 2048 MB | 16384 | fastest (15000 rpm) | As large as C but on a late-90s SCSI-grade spindle: about 4 minutes in Fast mode, 18 minutes in Realistic. |

There is also Drive G, the visitor's own. Its size (8 to 8192 MB) and speed
(3600 to 15000 RPM) are set in Settings and saved in the browser, so it can stand in
for whatever drive the visitor remembers owning. It runs on the same cluster
scale and timing model as the four above.

Roughly 60% of each disk holds data when generated, and about 2% of clusters
are unmovable.

## Interface

The window reproduces Windows 98 chrome: title bar with minimize, maximize and
close controls, a drive selector, Start, Pause and Stop buttons, a progress bar
with a percentage, an estimated time to completion, and a Legend button.

The Legend dialog lists the six cluster states exactly as Windows 98 did:
unoptimized data, optimized (defragmented) data, free space, data that will not
be moved, data that's currently being read, and data that's currently being
written.

Maximize expands the window to fill the viewport, which widens the cluster grid
without rescaling the clusters. The details pane auto-scrolls to follow the
defragmentation frontier, snapping to the next region as the visible one
finishes, and pauses that auto-follow if you scroll away yourself.

Settings let you pick the drive, choose between the Fast and Realistic
simulation modes, and mute the hard-disk sound effects and the mouse click
sounds independently. Those preferences persist in local storage.

Every control carries a Windows 98 access key: the letter is underlined in its
label, and Alt plus that letter presses it, so Alt+S starts a defragmentation
and Alt+T stops one. OK and Cancel have none, because Enter and Esc already
reach them.

Completing a defrag plays the Windows 98 "tada" chime.

There is an easter egg: clicking the title bar's close button has a one in four
chance of crashing the whole page to an authentic Windows 9x Blue Screen of
Death. Pressing any key or clicking anywhere recovers.

## Frequently asked questions

### Does Defrag98 touch the files on my computer?

No. It has no access to your disk and never reads, moves or modifies a single
real file. Every drive it displays is invented.

### Is it free?

Yes, completely, and there are no ads or sign-ups. Supporting it via Buy Me a
Coffee (https://www.buymeacoffee.com/morellodev) is optional; a coffee costs 3
euros.

### Does it work offline?

Yes. It is an installable progressive web app. Once loaded, the interface, the
fonts and the hard-disk audio are cached, and it keeps running with the network
switched off.

### Does it work on a phone or tablet?

Yes. On a small screen you first get a period-appropriate dialog saying Windows
98 is not supported on mobile devices. That is a joke, and dismissing it runs
the simulator normally.

### Why does every run look different?

The disk is generated fresh each time and the defragmenter decides what to do
as it goes, choosing between consolidating in place, relocating a chunk forward
and evicting a run out of the way.

### Which drive should I pick?

C for a long, grinding session, since it takes the longest of the four. F to
watch it finish quickly. E for the slowest, most laborious individual passes,
and D for something in between.

### How long does a full defrag take?

It depends on the drive and the mode. In Fast mode C is the longest at roughly
8 minutes and F the shortest at roughly 2. E has the slowest disk in the set,
so its passes are the most laborious, but it is only a quarter of C's size and
finishes in about 4 minutes. Realistic mode multiplies all of those by about
four and a half. The window shows a running estimate derived from the disk's
speed and how many clusters are left.

### What is Realistic mode?

The answer to everyone who says a defrag was never this quick. Realistic moves
at most 6 clusters a pass rather than 24 and triples every delay, so drive C
takes roughly 38 minutes rather than 8. Windows interrupts it once or twice
along the way: the progress line reads "Drive's contents have changed:
Restarting...", the drive is rescanned from the top, part of it comes back
fragmented, and the bar drops back. The run still finishes. Dismiss the
completion dialog and it stays at 100 percent. Fast mode is the default and is
unaffected.

### Is this the Windows 95 or the Windows XP defragmenter?

The Windows 98 one. Windows 95 shipped a near-identical defragmenter, down to
the cluster grid and the legend behind the Show Details button, so Defrag98
works as a Windows 95 defrag simulator too. Windows XP is not the same thing.
Its defragmenter drew horizontal bands instead of a grid of clusters.

### Can I just leave it running and watch?

Yes. Maximize the window, pick C, which takes the longest of the four, and it
runs to the tada chime with no further clicking. Windows interrupts a Realistic
run once or twice before it finishes. Leave it on a desktop rather than a phone:
nothing is saved between page loads.

### Is it related to the real Windows 98?

No. Defrag98 is an independent recreation and is not affiliated with or
endorsed by Microsoft. It runs no Microsoft code and contains no Microsoft
software.

## Detailed technical reference

https://defrag98.com/how-it-works is the primary source on the simulation
itself: how a fragmented drive is generated, what the defragmentation frontier
is, the three moves a pass can choose between (optimize in place, relocate
forward from a random source run, evict the frontier out of the way), the
seek-plus-transfer cost model behind the pacing and the time estimate, how the
cluster grid is drawn to a virtualized canvas, and which details are
deliberately unfaithful to the original.

## How it is built

A client-rendered React application written in TypeScript and built with Vite.
The cluster grid is drawn to a canvas element, viewport-virtualized so the
backing store stays small no matter how large the disk. State lives in Zustand
stores. Styling is Tailwind CSS over a palette of Windows 98 tokens, with MS
Sans Serif and an IBM VGA bitmap font loaded as web fonts. Offline support
comes from a Workbox service worker. It is hosted on Cloudflare Workers as
static assets.

## Privacy

The only thing stored in the browser is a `defrag98-preferences` key in local
storage holding the two sound toggles, the simulation mode, and whether the
unsupported device notice has already been shown. Traffic is measured with
Cloudflare Web Analytics, which sets no cookies and does not fingerprint
visitors. The full policy is at https://defrag98.com/privacy.

## Coverage

- PC Gamer: https://www.pcgamer.com/hardware/if-you-miss-defragmenting-your-c-drive-theres-a-website-that-lets-you-recreate-the-experience-complete-with-hard-drive-chunking-sounds/
- heise online: https://www.heise.de/en/news/Web-tips-Nostalgic-time-out-10327651.html
- Boing Boing: https://boingboing.net/2026/08/31/defrag-your-computer-like-its-1998.html
- kottke.org: https://kottke.org/26/08/0049538-the-windows-98-disk-defra
- Hacker News: https://news.ycombinator.com/item?id=49494036
- Datarecovery.com: https://datarecovery.com/rd/miss-defragmenting-your-hard-drive-this-website-is-for-you/
- byothe.fr: https://byothe.fr/en/windows-98-disk-defrag-simulator-defragmentation/
- Mezha: https://mezha.ua/en/2024/07/15/relax-a-developer-has-created-a-defragmenter-simulator-with-windows-98/
- Lobsters: https://lobste.rs/s/bx6852/windows_98_disk_defrag_simulator

## Author

Dennis Morello, a software engineer based in Milan, Italy.
Website: https://morello.dev/
Build notes: https://morello.dev/blog/windows-98-defrag-simulator