IBM 650 Simulator on macOS: Fixing the “Can’t Be Opened” Error and Getting It to Run

Field Notes: IBM 650 Simulator (app) vs. macOS Sonoma

I spent last night trying to get IBM 650 Simulator (app) running on my 14-inch MacBook Pro (M1 Pro, macOS Sonoma 14.4). The goal was simple and slightly nerdy: load a few sample punch-card programs and see if I could reproduce some classic 1950s workflows inside my modern OrchardKit setup. Retro computing therapy, basically.

Instead, I got stonewalled before the first virtual drum memory spin.

The Problem

First launch attempt from /Applications gave me:

“IBM 650 Simulator is damaged and can’t be opened. You should move it to the Trash.”

That wording again. “Damaged.” As if I downloaded a broken binary. I’ve seen this enough times to know it usually means Gatekeeper doesn’t like something about the code signature or notarization.

Apple explains how Gatekeeper works here:
https://support.apple.com/guide/mac-help/protect-your-mac-from-malware-mh40596/mac

But knowing the theory and fixing it are two different things.

Attempt #1 — Redownload Everything

My first move was the obvious one: delete the DMG, re-download, verify the file size, mount again, drag to Applications. Same error. So it wasn’t a corrupt download.

I briefly considered that Sonoma might be flagging it for lack of notarization. Apple’s developer documentation on notarization makes it clear that modern macOS versions expect properly signed and notarized builds:
https://developer.apple.com/documentation/security/notarizing_macos_software_before_distribution

This simulator is more of a niche academic tool than a polished App Store product. Not shocking if the notarization pipeline wasn’t prioritized.

Attempt #2 — Right-Click → Open

Classic bypass method. Right-click the app, choose “Open,” confirm manually. Sometimes that forces macOS to present the override in Privacy & Security.

Didn’t work. Same “damaged” message. No override option appeared.

At this point, I suspected quarantine attributes were involved.

What Was Actually Going On

macOS attaches a com.apple.quarantine attribute to anything downloaded from the internet. If the system doesn’t fully trust the binary, it blocks execution before the usual “unidentified developer” flow even kicks in.

So I opened Terminal and checked:

xattr /Applications/IBM\ 650\ Simulator.app

Sure enough — quarantine flag present.

That’s when I stopped guessing and did what usually fixes these situations:

xattr -dr com.apple.quarantine /Applications/IBM\ 650\ Simulator.app

Then I launched it again.

This time, the error changed. Instead of “damaged,” I got the standard:

“Cannot be opened because the developer cannot be verified.”

Progress.

I went to System Settings → Privacy & Security, and now the “Open Anyway” button appeared. Apple documents that override process here:
https://support.apple.com/guide/mac-help/open-a-mac-app-from-an-unidentified-developer-mh40616/mac

Clicked it. Confirmed.

The simulator finally launched.

Midway Reference

While troubleshooting, I kept this page bookmarked because it specifically referenced IBM 650 Simulator behavior on macOS systems and hinted that Gatekeeper was the main blocker:
https://smohamad.com/education/35319-ibm-650-simulator.html

It didn’t hand me the fix directly, but it confirmed I wasn’t dealing with a corrupted build.

After Launch — Performance Check

Once it opened, everything behaved surprisingly well. Native Apple Silicon support was present (checked with file on the binary — arm64 included), so no Rosetta needed. If it had been Intel-only, Rosetta installation instructions are here:
https://support.apple.com/en-us/HT211861

CPU usage hovered around 12–18% while running a sample program. Memory footprint stayed under 150 MB. Not bad for simulating a 1950s mainframe on a fanless laptop.

No random permission errors. No sandbox complaints. The issue was purely launch security.

What Actually Fixed It

The working sequence:

1. Move the app to /Applications before launching.
2. Remove the quarantine attribute via xattr.
3. Launch once to trigger the developer verification warning.
4. Approve using “Open Anyway” in Privacy & Security.

That’s it.

What I’d Do If I Knew From the Start

I wouldn’t waste time re-downloading. I wouldn’t try launching from Downloads (which can trigger App Translocation and complicate things further). I’d go straight to checking extended attributes.

Modern macOS is aggressive about unsigned software. It’s not malicious; it’s doing its job. But the “damaged” wording is misleading. The app wasn’t broken. It was blocked.

After clearing quarantine and manually approving it, the IBM 650 Simulator integrated cleanly into my OrchardKit workflow. I was able to load card decks, run basic arithmetic routines, and export logs without any instability.

In the end, the fix took about three Terminal commands and one trip into Security settings.

Half an hour of friction. Five minutes of actual solution.

Classic macOS.