How are macOS computers able to remember WiFi networks after FULL erase?

[alexmartinpc]

Hi, I was fixing a MacBook Pro that wasn't working correctly, and the very first thing I did was to take out the HDD and fully erase it, all partitions, everything. I proceeded to put a new HDD, installed Catalina, everything offline, no sync or downloading from servers. After that, I joined my private network, checked that everything was OK, and days later I replaced the HDD by a brand new SSD. Started from zero again, and what was my surprise, the WiFi network was already added. I did not log in with an Apple ID or anything storing or syncing keys in either of the occasions.

So, the question is... where does macOS save the WiFi password?
Since it's not the internal storage drive because I put a brand new one, what memory is left that is permanent?
How can I delete that memory info?
Does it contain anything else besides WiFi networks? Account names? Other settings?
Why Apple would store the WiFi networks somewhere else than the main storage?

 

[MacCheetah3]

Did you log into your Apple ID? Password encrypted Wi-Fi network connections are saved to the Keychain and thus synced with all logged in devices (by default).

 

[alexmartinpc]

No I didn't, edited that in the main post. Clearly it's something local, not taken from any account since I did not log in with any account.

 

[chrfr]

No I didn't, edited that in the main post. Clearly it's something local, not taken from any account since I did not log in with any account.

Wireless networks can be stored in the Mac's NVRAM.

 

[MacCheetah3]

The only other possibility offhand is NVRAM, which is indeed claimed by at least one person:

Where does Macbook Pro store wifi information?

Last December I connected to a wifi network with a password. A couple weeks ago I got a new hard drive for my computer. Today, I reconnected to that wifi network (this is the first time since I cha...

apple.stackexchange.com

However, that’s unverified, as far as my research turned up.

What’s stored in NVRAM?

Listing of known NVRAM variables and their usage/meaning, together with notes on how to change them.

eclecticlight.co

 

[appltech]

Considering that you can connect to a WiFi network when selecting startup disk (Option key on startup), e.g. before the OS boots; and a mac remembers this network later; I'd say yes, definitely NVRAM stores it. So, when fully erasing your Mac, reset NVRAM too.

 

[alexmartinpc]

Yes and no... right now, if I turn off the MB and reset the NVRAM, I still can connect to my network. What resets is the sound and something else I believe...

 

[MacCheetah3]

What resets is the sound and something else I believe...

The Eclectic Light article above is more thorough, but Apple doesn’t even mention Wi-Fi.

Settings that can be stored in NVRAM include sound volume, display resolution, startup-disk selection, time zone, and recent kernel panic information. The settings stored in NVRAM depend on your Mac and the devices that you're using with your Mac.

Reset NVRAM on your Mac - Apple Support

If one or more settings stored in NVRAM don't work as expected on an Intel-based Mac, resetting NVRAM might help.

support.apple.com

To me, Wi-Fi networks would be significant enough for inclusion in that short list.

 

[09872738]

Please: The computers are called „Mac“. MACs is something very different: Media Access Control; the thread title is kinda confusing.—

 

[svanstrom]

Yes and no... right now, if I turn off the MB and reset the NVRAM, I still can connect to my network. What resets is the sound and something else I believe...

But then you don't do a completely wipe at the same time as you've reset the NVRAM, correct?

So that's like having a cup of water in each hand, putting down one, and getting surprised that you still have a cup of water in the other hand… Two sources of the WIFI credentials, and you never delete both at the same time.

 

[Quackers]

I've done a number of re-installs on my M1 Air and sometimes it has automatically joined my netowrk (wifi) after erasing the Mac and other times it hasn't.
After the first couple of times it did rejoin automatically I assumed that it must be kept in NVRAM. Then it refused a couple of times so I don't know now

 

[alexmartinpc]

I've done a number of re-installs on my M1 Air and sometimes it has automatically joined my netowrk (wifi) after erasing the Mac and other times it hasn't.
After the first couple of times it did rejoin automatically I assumed that it must be kept in NVRAM. Then it refused a couple of times so I don't know now

Yeah, exactly, looks like a random lucky process... what really bugs me is, if MB is working badly and I want to completely erase every software and start from zero, then I proceed to erase and even swap the internal storage, and suddenly I still get piece of the old software, something wasn't wiped at all...

Please: The computers are called „Mac“. MACs is sonething very different: Media Access Control; the thread title is kinda confusing.—

Yeah, didn't think bout that. Changed title. Apple computers are often referred as MAC. "I have a MAC in home", or "I'm a MAC guy", hence, MAC in plural is MACs.

But then you don't do a completely wipe at the same time as you've reset the NVRAM, correct?

So that's like having a cup of water in each hand, putting down one, and getting surprised that you still have a cup of water in the other hand… Two sources of the WIFI credentials, and you never delete both at the same time.

That's what I was thinking, but then again, it's kind of weird that when you join a network, it is saved in 2 different storages.

Basically I wanted to make sure I deleted every permanent storage a Mac could have. In PC, if you swap the main disk you pretty much delete absolutely everything. You might reset the BIOS so the parameters restart, but that really fan control and that kind of stuff, not software that can affect your OS neither personal data.

For example, imagine a MB is working very laggy when you turn on the WiFi and can't connect to other networks because an app somehow put 5000 networks addresses with their passwords in the list, and it starts to check all of them. It's just an example... if I happily swap the HDD, the problem is not gonna solve, and I would freak out as I just thought I had erased everything and started from zero.

To sum up... according to you, you have to swap the HDD AND erase the NVRAM in order to delete every single personal data from a Mac, right?
If later you install with an USB Catalina, you should get a completely reset MB?

 

[svanstrom]

To sum up... according to you, you have to swap the HDD AND erase the NVRAM in order to delete every single personal data from a Mac, right?

As things changes over the years I would approach properly wiping a device by looking up exactly all the ways to reset different aspects of that particular device… There's NVRAM, PRAM, SMC, and all kinds of partitions etc. And the different levels of ways of wiping different types of storage.

Not to mention that there's also things like whether or not the hardware is registered to a particular account, and the dreaded (on the secondhand market) firmware password.

Basic(-ish) awareness and a quick websearch is enough if you've been around the block a couple of times; but it can definitely be a bit overwhelming for someone new to the Apple ecosystem.