# 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: 2026-10-01

## 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 colored clusters gather at the front of the drive 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. Below it is an icon for
Disk Defragmenter, which reopens the window after you close it. A How It
Works shortcut opens the page of the same name. A Win95GPT shortcut opens
https://win95gpt.com, a Windows 95 ChatGPT client made by Jimi Plouffe (https://x.com/JimiPlouffe).
Desktop icons behave as in Windows 98: a click selects one, a double click or Enter opens it
(on a touch screen, one tap), the arrow keys move between them, and typing a letter jumps to an icon whose name starts with it.
Dragging a box across the empty desktop with the mouse selects every icon it touches.

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.

Each ordinary pass shows green reads before red writes, then the clusters
settle into their resting colors. The layout and progress change after the
write flash. Data moved out of the way flashes green only; red marks writes
into the consolidation zone. Reading, writing and settled colors share the
pass's time budget equally. Evictions give the write phase's share to reading.
Browser scheduling can stretch the duration, especially in a background tab.

Pause freezes the current phase and Resume continues its remaining time. Stop
clears the flashes and keeps the last committed layout, discarding an unfinished
move. The last pass settles before the completion dialog opens.

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's estimate is about 13 minutes in Fast mode.

Realistic moves at most 6 clusters a pass, so the write head crawls rather than
jumping, and multiplies every delay by three. Drive C's estimate is about 61
minutes in Realistic mode. 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.
Between 2 and 5 percent of the drive's data comes back fragmented, as if a
program had rewritten a few files while the defragmenter worked. The rest of
the finished work stays where it was. The bar drops back a little and
consolidation resumes. 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 a few files, where the original resumed from where it
had stopped and lost only time. Without that, the interruption would barely
register in a simulation with no programs writing real files. Everything else
you had consolidated stays put.

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, with Minimize, Maximize and Close controls
in the title bar, and dragging a border or corner resizes it. Below the cluster map are a progress bar, a percentage, and
Start, Pause and Stop controls. Settings contains the drive selector and a
whole-run estimate; Legend explains the cluster colors.

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, stopping above the taskbar. The title bar's
Minimize button hides the window. Its taskbar button activates or restores it,
or minimizes it if already active. Clicking the desktop leaves the window
visible but inactive. Close quits Disk Defragmenter and abandons the run in
progress. To open it again on a freshly fragmented drive, double-click or tap its desktop icon or
pick Disk Defragmenter under Programs, Accessories, System Tools. Typing defrag in
the Run box works too. A defragmentation keeps running while the window is
minimized, and the window reopens by itself when the run finishes. 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. Settings also has a checkbox, off by default, for a
screensaver mode: Start takes the page full screen until the run ends. Safari
on iPhone can't do that, so Settings leaves the checkbox out there. The
speaker icon in the taskbar's notification area mutes every sound at once and
leaves those settings untouched. The clock beside it shows your computer's time.
Those preferences persist in local storage. Changing sound settings or
simulation mode keeps the cluster map and progress, including a paused phase.
Selecting another drive or changing the custom drive's size or speed generates a
fresh disk.

The Start button on the taskbar opens a Windows 98 Start menu, and so do Ctrl+Esc
and the Windows or Cmd key pressed on its own. Disk Defragmenter, under Programs,
Accessories, System Tools, brings the window back, or opens it again after you close it. Programs also has a Win95GPT
link. Favorites links to Buy Me a Coffee and Dennis Morello's website and X profile.
Documents and Help open the
site's pages, and Windows Update opens the release notes. Run... opens the
Windows 98 Run box. Typing defrag there opens Disk Defragmenter, and the box fills in the last command next time. Any other command gets the Windows 98 "Cannot find the file"
error, except bsod, the easter egg below. Log Off and Shut Down don't work here. They open the Windows 98
Restrictions message, which tells you to contact your system administrator.
Alt plus an underlined letter runs a menu command.

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 instead of closing the window, and typing bsod in the Run box crashes it every time. Pressing any key or clicking anywhere restarts the page like Windows 98
after a bad shutdown. ScanDisk checks drive C, then the Windows 98 logo appears
and the app returns. Exit skips the scan.

## 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.

### What do the green and red blocks mean?

Green shows data being read, then red shows where it is written. The blocks
settle into their resting colors before the next pass. Data moved out of the
way flashes green only; red marks writes into the consolidation zone. Pause
freezes the current phase, and Resume continues it.

### 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
13 minutes and F the shortest at roughly 4. 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 those estimates by about
four and a half, before rescans and the files they refragment. Settings shows an
estimate for a whole run, not a countdown of the current one.

### Will changing settings reset my progress?

Changing sound settings or simulation mode keeps the cluster map and progress,
including a paused phase. Selecting another drive or changing the custom drive's
size or speed generates a fresh disk.

### What is Realistic mode?

A slower simulation you turn on in Settings. Realistic moves at most 6 clusters
a pass rather than 24 and triples every delay, so drive C's estimate is about 61
minutes rather than 13. 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, a few files come back
fragmented, and the bar drops back a little. Most of the finished work is kept.
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. One section explains why Windows 98
kept restarting a defrag, citing Microsoft KB 186171 and KB 186978, both
retired and archived.

## How it is built

Astro builds the static pages and loads the TypeScript simulator as one
client-side React app, mounted from a module script.
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 `defrag98-preferences` key in local storage holds the sound settings,
whether the taskbar mute is on, simulation mode, selected drive, custom drive
size and speed, desktop icon visibility, whether the unsupported device notice
has been shown, and the completion count used to time donation requests. The service worker also caches
the app's files for offline use. 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.

## Author

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

## Latest release

### 2026-10-01: Desktop icons, closable windows, Run

- Desktop icons now work as in Windows 98: a click selects one and a double click opens it, while on a touch screen one tap opens it. Disk Defragmenter has a desktop icon too.
- Windows can now be resized, and Close now closes Disk Defragmenter. Open it again from its desktop icon, from System Tools in the Start menu, or by typing defrag in Run.
- Run... in the Start menu now opens the Windows 98 Run box. Type defrag to open Disk Defragmenter or bsod for a blue screen, and anything else gets a "Cannot find the file" error.