After purchasing an Apple Si M1 - based Mac , the great unwashed have discovered that an external startup bulk used with an Intel Mac wo n’t boot the Modern computer . Apple has organized hidden partitioning that are part of the startup process differently for macOS bulk that handle Intel and M1 Macs . As far as anyone understands and has try , you ca n’t make a dual Intel / M1 bootable startup drive . ( If you get it on otherwise , countenance us bed . )
That ’s generally not that big of a trouble . Most people who are n’t system administrators rarely postulate a style to start up a computing machine outwardly when that drive is n’t go down up as the default startup drive . The situation asserts itself mostly when you need to migrate from an Intel Mac to an M1 Mac while using the same external drive and you did n’t purchase a Mac with an internal volume large enough to habituate Migration Assistant to hold back your outside startup ’s contentedness .
This take place to me recently . I had upgrade my 2017 Intel iMac to an outside Thunderbolt 3 SSD in 2020 because its inner Fusion drive could n’t keep up with my work . It made a Brobdingnagian conflict in carrying out . When the iMac ’s motherboard die a few weeks ago , well out of warrant , I shifted to an M1 Mac mini with a tiny intimate drive , as I already had a high - performance 1 TB SSD and did n’t want to pay the high cost for that mental ability with the Mac mini .
However , like some readers who have write in about the situation , I could n’t boot from my Intel - target external drive . I want to kick upstairs the international drive to work with an M1 , and that required do a little saltation with an extra drive of gamy - enough content to stack away everything from my external startup drive .
This operation is simplify by the arrangement / information bulk split in macOS 10.15 Catalina and afterward . Instead of a single inauguration volume that has all the system and data point data file , Apple break macOS into two spell for greater surety . When you clone Big Sur ( or the upcoming Monterey ) to migrate it in this process , you only need to copy the Data bulk , as the system mass has to be created as part of the macOS installing or upgrade process .
There are two paths you may take . But before you start down either , ensure you have a full clone of your Intel Mac ’s Data bulk . If you ’re already using Time Machine , you should still make an additional copy because Time Machine is fragile and sometimes undependable .
Ihighlyrecommend using a Time Machine backup for this external - drive system switchover . In my examination , the Time Machine way seemed to lick better than bank on a disk clone of an Intel inauguration mass — at least a twosome of months ago . Apple keep ameliorate its migration tools , but macOS understandably likes its own backup format well .
If you pick out the path to make a clon , I preferCarbon Copy Clonerto make an identical copy , but Disk Utility will do the trick , too .
If you ’re using an SSD as the inauguration volume , you do n’t involve to bribe another SSD for this task if you do n’t already own one . You could purchase an cheap , high - mental ability hard disk drive ( HDD ) . Although using an HDD increases the time both to make a ringer and touch on it , the cost is so much lower than an SSD , and then you have that HDD available for Time Machine support afterwards .
Here ’s how to perform the migration :
The migration can take a long time , as you ’ll have experience if you ’ve gone through it before . The 800 GB of file I had took a few hour to send away into place . But when the migration was consummate and my new M1 Mac rebooted , I was dismiss mighty back into the minute my Intel Mac had died — much down to the minute .
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