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.sit, .sitx, and .hqx files on macOS

You found an old backup — a CD-R, a Zip disk, a folder carried across four Macs — and it’s full of files macOS refuses to open. .sit. .sitx. .hqx. Maybe .bin or .cpt.

None of them are broken. They’re all from an era when Mac files needed special handling to survive email and dial-up, and modern macOS quietly dropped the ability to read any of them.

Here’s what each one is and what still opens it.

The quick answer

ExtensionWhat it isWhat opens it in 2026
.sitStuffIt archiveThe Unarchiver (free)
.sitxStuffIt X (later format)The Unarchiver (free)
.hqxBinHex 4.0 text wrapperThe Unarchiver (free)
.bin / .macbinMacBinary wrapperThe Unarchiver (free)
.cptCompact Pro archiveThe Unarchiver (free)
.aceACE (Windows, 1990s)WinACE on Windows — see the warning below
.ddDiskDoublerThe Unarchiver, sometimes

If you take one thing from this page: install The Unarchiver. It’s free on the Mac App Store, and it handles the entire left column except ACE. It’s the only modern Mac tool that still does.

Purrchiver does not extract these formats. It identifies them and tells you what they are, so you’re not staring at a generic “extraction failed” — but the extraction itself belongs to The Unarchiver. We’d rather send you to the right tool than ship a half-working one.

What each format actually is

StuffIt (.sit, .sitx)

The de facto Mac archive format from the late 1980s through the early 2000s — the Mac’s answer to ZIP, from Aladdin Systems and later Smith Micro. If you downloaded anything on a Mac before about 2005, it arrived as a .sit.

Smith Micro stopped development around 2010. StuffIt Expander was a 32-bit app that broke with macOS Catalina and has been gone from the Mac App Store for years. There is no maintained open-source StuffIt reader — the only working extractor is XADMaster, which lives inside The Unarchiver.

.sitx is the later, incompatible format. Same answer.

There’s a detailed write-up of why this format is a dead end, and what the error message means, at how to open a .sit file on macOS.

BinHex (.hqx)

Not compression — encoding. BinHex 4.0 turns a Mac file, including its classic resource fork and Finder metadata, into 7-bit ASCII text so it could survive email systems and bulletin boards that mangled binary attachments.

You can confirm a file is BinHex by opening it in any text editor. The first line reads:

(This file must be converted with BinHex 4.0)

Decode it and you usually get a .sit — BinHex and StuffIt were near-always paired in downloads of the era. So expect two steps.

MacBinary (.bin, .macbin)

BinHex’s binary cousin, with the same goal: preserve Mac-specific file metadata across systems that didn’t understand it. Same tool, same answer.

Careful with the extension — .bin is heavily overloaded. A .bin file may be MacBinary, a disc image, a firmware blob, or something else entirely. Run file yourfile.bin in Terminal before assuming.

Compact Pro (.cpt)

A StuffIt competitor from the shareware era, common on bulletin boards. Rarer than .sit, same situation.

ACE (.ace) — a real warning

ACE was a proprietary Windows format from the late 1990s. It’s undocumented, and every open-source reader is reverse-engineered.

It also has a documented history as a malware vector: CVE-2018-20250 in WinACE’s unacev2.dll enabled widespread WinRAR exploitation, because WinRAR bundled the same vulnerable library. If you’ve been handed a .ace file from an untrusted source, the safest thing is not to open it at all. Purrchiver deliberately ships no ACE extractor for exactly this reason.

When The Unarchiver can’t open it either

  • Check it’s really the format the extension claims. Run file yourarchive.sit. Old media and old transfers produce a lot of mislabeled files.
  • Pre-2005 .sit files are the fragile ones. StuffIt 5 and earlier used format variants that even Smith Micro’s own later apps handled poorly.
  • The resource fork may be gone. This is the one that catches people. Classic Mac files stored half their content in a resource fork. If the file was ever copied through a Windows machine, a FAT32 drive, or most cloud sync, that fork was silently discarded — and what’s left may be unrecoverable. If you still have the original media, re-copy from it directly.
  • Try a different era of tool. A Mac OS 9 emulator (SheepShaver) running the period-correct StuffIt Expander will read things modern tools won’t. This is a real last resort, but it works.

Once they’re extracted

Old archives tend to yield more old archives, and often a pile of ordinary modern ones alongside. Purrchiver reads the whole modern set — .zip, .rar (including multi-part .r00/.r01 splits), .7z, every .tar.* variant, .iso, .dmg, .cpio — and it’s free to download and free to extract anything.

Get Purrchiver on the Mac App Store →