Yesterday an Apple Certified Macintosh Technician installed an SSD into my iMac medio 2011. The iMac was born with an 1TB HDD but now a Crucial M4 SSD is also installed inside the mac. I've moved my OS X to the SSD using the OS X Recovery, where the OS was installed using an Time Capsule Backup. Afterwards I did an Erase of the old HDD in Disk Utility to remove my old OS and my data has now been transferred to new, clean partition. Afterwards I inserted my Lion DVD and did an reinstall of the OS X to get the OS X Recovery partition created on my SSD. The name of the partition on the SSD is Crucial M4 SSD and the name of partition on my old 1TB HDD is Storage.

Please see this output from diskutil list:

iMac:~ dennis$ diskutil list/dev/disk0
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *256.1 GB   disk0
   1:                        EFI                         209.7 MB   disk0s1
   2:                  Apple_HFS Crucial M4 SSD          255.2 GB   disk0s2
   3:                 Apple_Boot Recovery HD             650.0 MB   disk0s3
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *1.0 TB     disk1
   1:                        EFI                         209.7 MB   disk1s1
   2:          Apple_CoreStorage                         999.9 GB   disk1s2
   3:                 Apple_Boot Boot OS X               134.2 MB   disk1s3
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:                  Apple_HFS Storage                *999.7 GB   disk3
  1. Why do I have an Apple_Boot on disk1 after the entire disk was erased?
  2. What is the EFI and Apple_Boot?
  3. Is it normal that the type of the Recovery HD is Apple_Boot?

1 Answer 1


Why do I have an Apple_Boot on disk1 after the entire disk was erased?

I am not sure on this one. Seeing the size (134 MB) I don' this this is the actual boot partition itself.


What is the EFI and Apple_Boot?

EFI is the Extensible Firmware Interface system partition. This is a special partition that holds boot loaders for all the OSes installed, in other partitions:

The EFI System partition is a partition on a data storage device that is used by machines that adhere to the Extensible Firmware Interface. It contains the boot loader programs for all operating systems installed (in other partitions) on the device, device driver files (used by the firmware at boot time) for other devices, and system utility programs that are intended to be run before an operating system is booted.1


Is it normal that the type of the Recovery HD is Apple_Boot?*

Yes. Otherwise you cannot use the recovery partition to recover when the OS on the other partition(s) has crashed, right?

The recovery partition is actually replacement of the OS install disk. From OS X Lion: About Lion Recovery

OS X Lion includes a new feature called Lion Recovery that includes all of the tools you need to reinstall Lion, repair your disk, and even restore from a Time Machine backup without the need for optical discs.

  • So your conclusion is that every thing except from * disk1s3* is perfect? Is there any chance that I can remove the disk1s3 without having to erase the entire disk?
    – dhrm
    Commented Apr 20, 2012 at 11:21

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