Drop in an old Mac file and open it
You have found a file from an old Macintosh — in a backup, on a Zip disk you finally read, at the bottom of an FTP mirror — and nothing on your computer will open it. Drop it here. It opens on an emulated Macintosh running System 7, in this tab, with nothing installed and nothing uploaded.
Everything happens in your browser. Your file is never uploaded anywhere.
What you can drop in
| Extension | What it is | What happens |
|---|---|---|
.sit .sea | StuffIt archive, the standard Mac compression format from 1987 onward | Copied onto the emulated Mac and expanded there with StuffIt Expander |
.hqx | BinHex — a Mac file turned into plain text so it could survive email and Usenet | Decoded in your browser, then handed to the Mac with its resource fork intact |
.bin | MacBinary — both forks and the Finder info in one file | Decoded in your browser, then handed to the Mac |
.img .dsk | A floppy or hard disk image | Mounted as a disk. It appears on the desktop. |
.toast .iso | A CD-ROM image | Mounted as a CD |
.cpt | Compact Pro archive, StuffIt's main rival | Copied across and expanded on the Mac |
.zip | A zip, possibly with a __MACOSX folder holding the resource forks | Unpacked, forks reattached where they exist |
.dmg .smi | Disk images from the Mac OS X era and self-mounting images | Older formats mount; newer compressed ones are extracted instead — see the DMG page |
Why old Mac files are so awkward
Every other platform's idea of a file is a single stream of bytes. The classic Macintosh had two: a data fork, which is the stream everyone else has, and a resource fork, a small structured database holding icons, menus, dialogue layouts, sounds, and often the executable code itself.
This was elegant on a Mac and catastrophic everywhere else. Copy a Macintosh application to a DOS floppy, an FTP server or a Unix mail spool and the resource fork silently vanished, leaving a file that looked intact and did nothing at all. Worse, the Mac did not use file extensions — it identified a file by a four-character type and a four-character creator code stored outside the file entirely, so a file that crossed platforms lost the knowledge of what it even was.
Every classic Mac format you will run into exists to solve some part of that problem. MacBinary wraps both forks and the type and creator into one ordinary file. BinHex does the same and then encodes the result as printable text so it could be pasted into an email body. StuffIt compresses and archives while preserving all of it. Disk images sidestep the question by copying the whole filesystem.
Which is why the reliable way to open one of these files in 2026 is to give it back to a Macintosh. That is what this page does.
Where the file goes
Nowhere. The emulator is WebAssembly running in this tab, and your file is read by JavaScript on your own machine and passed straight into the emulated Mac's memory. There is no upload, no server round trip, and no copy kept anywhere.
Anything you then save inside the emulated Mac is stored in your browser's own storage. It survives closing the tab. It does not follow you to another browser or another device, and clearing site data for this site will delete it.
Questions people ask
Is my file uploaded anywhere?
No. The emulator runs inside your browser as WebAssembly. Your file is read locally and passed into the emulated machine. Nothing is sent to a server.
What if my file has no extension?
Drop it in anyway. The loader looks at the actual bytes rather than the name — MacBinary, BinHex, DiskCopy and StuffIt all have recognisable headers.
Can I get a file back out of the emulated Mac?
Not yet. Getting files out is on the list; today the loader is one-way.
Why does my application launch and then immediately quit?
Usually a missing resource fork — the file travelled through something that stripped it. Look for a .hqx, .bin or .sit version of the same thing, which will have the fork preserved.
It says the disk is unreadable.
The image may be in a format the Mac does not recognise, or it may be a raw image with a DiskCopy header the loader did not strip. Try a .img or .dsk version if one exists.
Will a Mac OS X application work?
No, and not because of anything here — an OS X .app is a PowerPC or Intel binary that needs a Unix system underneath it, which is a completely different machine from the ones emulated on this site. The what runs page explains the line.