MacBook Migration Assistant: What It Carries and What It Leaves

Migration Assistant is the least examined app on a MacBook. Most people meet it once, inside the setup assistant of a new machine, click through it while the laptop is still in its box packaging, and never open it again. That is a shame, because the same app answers several later questions: bringing across a category that was skipped, reading a Time Machine disk from a laptop that has already been sold, or pulling a user account off a Windows PC.

What follows is where the app lives, what it can read from, which of its prompts have consequences, and the list of things that are outside its job entirely.

Three ways in, not one

Apple describes Migration Assistant as included with macOS both as an app and as part of the setup assistant that opens when a new Mac first starts up. The transfer documentation gives the two app routes: it can be found in the Utilities folder inside the Applications folder, or opened with Spotlight, and it asks for an administrator password before it will make changes.

The Mac User Guide adds a third, which is the one most people never find: System Settings, then General in the sidebar, then Transfer or Reset, then Open Migration Assistant. The guide's own framing is that if information was not transferred when the Mac was first set up, Migration Assistant can be used at any time to transfer documents, apps, user accounts, and settings.

That sentence is the useful part of the whole article. A laptop that was set up as a clean machine three weeks ago is not locked out of a migration. As long as the source still exists, whether as a running Mac, a Time Machine disk, or a startup drive, the transfer can still be run.

One practical note for laptops. Migration Assistant quits most of what is running and takes over the screen for the duration, so it is not something to start ten minutes before a meeting. It is also the reason Apple's preparation list says to connect a laptop to power, since a transfer can run for hours with the display awake the whole time.

The four things it can read from

The choice screen inside the app is short, and each option maps to a different situation.

A running Mac, connected over Wi-Fi or the same network, is the standard case. A Time Machine backup covers the laptop that is already gone or broken. Another startup disk covers a drive pulled out of an old machine, or one connected over the network. And a Windows PC is handled separately, with software installed on the PC side.

The Time Machine and disk routes matter more than their billing suggests. The Mac User Guide documents transferring from another disk on the Mac, a disk connected to it, a disk on the same network, or another Mac running OS X 10.8 or earlier connected with a Thunderbolt cable, in which case the T key is held while that machine restarts so it presents itself as a disk. The same five selectable categories appear as in a live transfer, so nothing is lost by migrating from a backup rather than from the machine itself.

The PC route has its own rules that surprise people. Apple's documentation states that information can be transferred over a wired or wireless network from a PC running Windows 10 or later, that Bluetooth needs to be on, and that Windows Migration Assistant has to be downloaded and installed on the PC for the version of macOS on the Mac. It also notes that transferring several users means logging in as each of them and running the tool again, once per user.

The handshake, and the prompts that have consequences

Both machines run the app at the same time and they choose opposite directions, which is where a first attempt usually goes wrong.

On the new MacBook, the option is to transfer from a Mac, Time Machine, or startup disk. On the old one, the option is to transfer to another Mac. The new machine then picks the old one from a list, and a security code appears on both screens. Apple's instruction is to confirm that the code matches before continuing, which is what stops a transfer going to the wrong laptop on a shared network.

Preparation decides whether the two machines see each other at all. Apple's list is short: install available macOS updates on each Mac, with the explicit note that it is not necessary for both to be running the same version; have Wi-Fi on with the machines near each other, joined to the same network if either is running OS X El Capitan or earlier; connect a laptop to power; and turn off antivirus, firewall, or VPN software until the transfer is finished. That last item is the most common reason a Mac never appears in the list.

Two prompts during the transfer have lasting consequences. When an administrator account is transferred, Apple documents a prompt to click Set Password and enter a secure password, which is then the login password for that account on the new Mac. When a standard account is transferred, a temporary password is assigned and shown on screen, and Apple's instruction is to write it down because the user must enter it at first login before setting their own.

The third is about collisions. If an account with the same name already exists on the new MacBook, the options are to replace it, sometimes with the chance to keep a copy of the replaced data in a Deleted Users folder, or to rename the incoming account so both are kept and can be logged into separately. Renaming keeps both, which makes it the recoverable choice.

What it carries

The selection screen is the real specification, and it has five entries. Apple's guide lists them by name.

Applications transfers apps to the new Mac, with the documented caveat that incompatible apps, or apps with newer versions already installed, may not be transferred or may not be usable. User accounts can be expanded with the disclosure arrow to choose specific items inside an account, such as documents, pictures, movies, desktop, and the downloads folder. Other Files & Folders covers documents and files outside those accounts. Privacy & Security Settings and System & Network transfer settings, with the second also expandable to pick individual items.

Before the selection appears, the app calculates how much storage is used by everything it can see, including applications, user accounts, files, folders, and settings. That number is what the checkboxes are measured against.

At the end, the Mac restarts and shows a migration summary if issues were found, with documents that could not be transferred and incompatible software detected given as the two examples. This is the only point at which the system volunteers what it failed to do, and closing it unread is the most expensive click in the process. Apple also notes that large transfers might need hours and might seem to pause occasionally, and that Migration Assistant should be quit on both machines afterwards.

What it leaves

Anything that is not one of those five categories is not part of the transfer, and the pattern in what falls outside is consistent: files travel, secrets do not.

Apple states it directly for mail. Migration Assistant transfers email, but to access it the email account might first need to be set up again in the email app. Messages are files and files move; account passwords and tokens belong to a keychain that a new laptop is not automatically a trusted holder of.

The PC documentation says the same thing with less hedging. For computer settings, the desktop picture, selected language, and location are transferred, and network settings and passwords are not. That article is about a different source machine, but the principle it exposes applies across the board.

Files kept in iCloud were never in scope either. Apple's page on Desktop and Documents in iCloud Drive explains that turning the feature on stores both folders in iCloud Drive, and that the process has to be repeated on every Mac to be used with iCloud Drive. Those files arrive because the laptop signed in, at whatever speed the connection allows, and certain library files are never uploaded from those folders at all: iMovie, Photos, and Aperture libraries, labelled Ineligible in the Finder.

The word incompatible in the Applications caveat has a specific meaning on current laptops, and it is a moving target. Apple states that Rosetta, the translation layer for Intel-based apps on a Mac with Apple silicon, is available for any Mac with Apple silicon using macOS 27 or earlier, and that starting with macOS 28 its functionality will be available only for certain older, unmaintained games that rely on Intel-based frameworks. An Intel-only app carried across today can open on the new MacBook and stop opening after a later upgrade. Apple's advice is to replace such apps with a Universal or Apple silicon version rather than rely on translation, and it notes that plug-ins, extensions, and updaters may need updating separately.

Item	Part of the transfer	What is left to do
Documents and folders	Yes, per account or as other files	Nothing, if the source held them locally
Applications	Yes, with exceptions	Reactivate licences, replace incompatible builds
Mail	Messages yes	Set up the account again in the email app
Network settings and passwords	Not from a PC	Rejoin networks, re-enter credentials
iCloud Drive files	No, by design	Sign in, enable the setting on this Mac
Browser sessions and second factors	No	Sign in service by service

The sign-ins are the real remainder

Add up everything in the right-hand column and one item dominates. Not the files, not even the apps, but the number of services that have to be logged into again by hand.

For most working setups that list is no longer three desktop applications. It is a mail account, a calendar, a chat tool, a project tracker, two or three assistants, a design tool, a cloud console, and a second account for half of them. Each one means a sign-in, a verification prompt, a wait for a code, and then the same again for the other account of the same service, which is the point at which browser profiles get created in a hurry and never labelled.

That work is unavoidable once. It is avoidable the second time, and a migration is the only moment when the arrangement is exposed clearly enough to redesign. Keeping each web app in its own persistent space with its own cookie container means two accounts on one service stay signed in side by side, and a list of workspaces that syncs through a personal iCloud or Google Drive folder turns the next laptop into a restore rather than another afternoon of codes.

What to change first

Before starting, update both machines, connect the laptop to power, and switch off antivirus, firewall, and VPN software. After it finishes, read the migration summary instead of dismissing it, and write down the two lists it gives. Then work through the sign-ins as one deliberate task, giving each service that has more than one account its own window, which is what SpaceDeck is built to keep once the files are already in place.