Mac OS X: Disk Appears Dimmed (or "Grayed Out") in the Installer

On certain computers, Mac OS X cannot install on a volume that is not completely contained within the first 8 GB of an ATA hard disk. Other possible causes that affect any Mac OS X-compatible computer are listed at the bottom of this article.
This article has been archived and is no longer updated by Apple.
This information is also available in the Before You Install document included with Mac OS X.


A volume appears dimmed or "grayed out" in the Mac OS X Installer. You cannot select it as the install destination.

Note: "Volume" in this instance refers to either an ATA hard disk or an ATA hard disk partition.

SCSI hard disks may not be affected, regardless of their storage capacity.


If you do not have one of the computers listed specifically in the "Products affected" section, skip down to the "Additional Causes" section.

On the listed computers, Mac OS X must be installed on a volume that is contained entirely within the first 8 GB of its ATA hard disk. You may partition your hard disk to facilitate installation.

Note: Even if your hard drive was sold as having an 8 GB capacity, it may still be affected. Many hard drive manufacturers slightly understate the actual size of their hard drives to account for the space which is used in formatting. A hard drive sold as having an 8 GB capacity may actually be 8.25 GB, for example.

This generally breaks into three scenarios:
    1. The hard disk is larger than 8 GB and is not partitioned.

    In this circumstance, you may partition the disk to create a volume that falls entirely within the first 8 GB of the disk.

    2. A partitioned hard disk has at least one volume in the first 8 GB.

    For example: If you had a 12 GB disk divided into three partitions of 3 GB , 3 GB, and 6 GB, respectively, then the first and second would be available to the Installer and the third dimmed. You could choose to install only on the first or second partition. If the first two partitions are already full, you could start up from a Mac OS 9.x CD to backup data from one of the first two to the third partition, then empty or erase the backed-up partition to free space for Mac OS X.

    3. A partitioned hard disk does not have a volume in the first 8 GB.

    For example: If you had a 20 GB disk divided into two equal partitions, both would appear dimmed in the Installer, since neither partition would be contained within the first 8 GB. In this circumstance, you may partition the disk to create a volume that falls entirely within the first 8 GB of the disk.

How to partition the disk

Warning: Always backup data you wish to keep before initializing and partitioning a hard disk. Initialization erases all data on the hard disk.

Important: If your hard disk was sold as 8 GB and appears affected by this issue, you should create at least two partitions to ensure that the symptom does not recur. The second partition could be just enough megabytes of unallocated space to offset the actual size of your disk, or it could be a significant portion. The choice of how to manage the disk space is up to you.

Steps to initialize and partition the startup disk:
    1. Start up the computer from the Mac OS X 10.0 Installation CD-ROM.
    2. At the first screen, choose Open Disk Utility from the Installer menu.

    Note: Do not click Continue. If you do, you must restart from CD. There is not an option for going back.

    3. Select Drive Setup.
    4. Select the hard disk you are going to partition.
    5. Click the Partition tab.
    6. Set up the desired partition scheme and format.

    Note: This is the critical step for this issue. Be sure that the first partition stays within the first 8 GB of the disk.

    7. Click Partition.

After the process is complete, you may install Mac OS X on the disk.

Additional Causes

The following circumstances may cause a volume to appear dimmed in the Installer on any Mac OS X-compatible computer. In Mac OS X 10.1 and later, you can move the mouse pointer over a dimmed volume to reveal more information about why the volume is unavailable.
    1. The volume does not have enough available space to accommodate the installation of Mac OS X.
    2. You are attempting to install an incompatible Mac OS X (client) update when Mac OS X Server is already installed. Not all Mac OS X updates can be installed with Mac OS X Server. A message to this effect may appear when you move the pointer over the volume in question.
    3. The disk format of the affected volume is not compatible with Mac OS X or cannot be converted by the Installer. For more information see technical document 106229: "Mac OS X 10.0: Does Not Recognize and Cannot Be Installed on UFS Disks Formatted by Drive Setup 1.8.1"
    4. The volume is read only, such as a CD-ROM disc.
    5. The volume is of a type that cannot be used as a Mac OS X startup disk. USB hard drives, for example, are not fast enough to be Mac OS X startup disks, though they work normally as data volumes.

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Published Date: Oct 7, 2016