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This page was spun off of a User
contributed FAQ due to space
considerations on the FAQ page. In
addition, before doing any of these
procedures, the precautions outlined on
the upgrade FAQ
are recommended. But you should keep in
mind the difference between each of these
procedures below once precautions have
been taken.
"Clean install" is not a Tiger (Mac OS X
10.4) installation option, nor an option
to any version of Mac OS X. If you hear
people say "Clean Install" about Mac OS X,
please correct them as that is not the
term Apple uses for Mac OS X installation.
Windows users are used to a clean install
process which closely approximates the Mac
OS X "Erase and Install." Mac users who
have used Mac OS 9 and earlier, are used
to a clean install process which closely
approximates Mac OS X Archive and Install.
As such it is recommended you only use the
term Apple uses in its installer so that
when other people discuss with you what
installation to perform, your
communication is clear. Otherwise one
person may think you meant to erase the
hard drive, while another thinks you only
meant to disable the old operating system
folder, and create a new one.
Clean install is what you do to Mac OS 8
and 9 ( 8.0, 8.1, 8.5, 8.6, 9.0 - 9.2.1)
when you create a new System Folder, and
rename the old one Previous System Folder
and have to manually move Preferences,
control panels, and extensions over to the
new system folder from your old
application installations.
In Mac OS X, you have five installation
options, one of which is like a Clean
Install but goes under a different name.
There is:
1. Erase and install - erases the hard
drive and installs a fresh copy of the
operating system. Currently not
recommended because of a bug which
began in 10.3 that has caused some
Firewire hard drives to become unreadable
after installation of 10.3 or later.
Unless of course you have two copies
external of your internal hard drive of
every critical file and know how to access
them easily, erase and install will only
leave you with the backup of your data,
assuming the backup is accessible after
the installation of the system. With 10.3
or later, there are no guarantees this
will be the case with external Firewire
hard drives. The problem has been narrowed
down to Oxford 922 and 911 drives and
Apple is working to solve this problem.
Note: When you erase and install, and if
your machine is Mac OS 9
bootable, you need to make sure to add Mac OS 9 drivers when
erasing the system to ensure that
Mac OS 9 booting can happen after an erase
and install.
For all intents and purposes, if instead
of actually choosing erase and install,
you use Disk Utility, or some other
formatter to erase your hard drive before
installation, you will have done the same
thing as an erase and install. Granted,
there is the zeroing with a Disk Utility
which is not what an Apple erase and
install does, but for purposes of
simplicity and clarity, make sure when
discussing what you do to install that you
did this, rather than erase and install or
clean install.
Another unintended side effect of an erase
and install is that additional
applications which were installed on the
Mac initially have to be restored
separately. With all other installation
options on this page, the original
applications which came with the Mac are
preserved. To find out which original
applications came with your Mac, I've
constructed the Installed
Applications on Mac OS X FAQ.
Recovery partitions on 10.7 offers Disk
Utility to do an erase, and then will
allow you to reinstall the OS
that shipped with your Mac, or the
most current OS installed.
Directions for recovery are available for
Intel
Macs, and M1
Macs.
Internet Recovery recovers the first
system that shipped with the Mac, which is
recommended only if you first backup your data
and wipe the drive.
If you use just simple recovery, backup your data
first, then run it from the main recovery
screen without wiping your system, if all
you want to do is make sure the current
system isn't missing any components that
are part of the operating system. Use Disk
Utility to wipe the system only if you
feel the system is unusable and you need
to wipe it. When you use Disk
Utility from recovery to wipe from
recovery, be sure to wipe the top
most partition after selecting View menu
-> Show All Devices.
If wiping to restore Sierra
(10.12.6) or earlier, be sure to
reformat the disk utility Mac OS
Extended Journaled. APFS won't
work with it.
2. Restore system - restores the operating
system and any applications that came with
the Mac. Apple's Knowledgebase
Article 61802, and 301486
describes several methods of restoring
your system.
3. Archive
and Install - first appeared under
retail 10.2 CDs, and later to became
available on 10.3 update CDs, in addition
to 10.3 and 10.4 retail. It is unknown at
this time if the 10.4 update CDs have this
option. This gives you the option to
create a new system folder, while renaming
the old, and save user and network
preferences. If you don't save user and
network preferences, your installed
applications that are non-Apple, and your
Users folder get moved to the Previous
System folder along with the previous
operating system. This is the one most
like the Mac OS 8 and 9 Clean Install
option, but it is not called that by
Apple. This is the currently recommended
way to install a new operating system to
make sure you preserve your data. Archive
and Install may leave behind newer
applications than will run with the
operating system if you Archive and
Install 10.2 over 10.3. It is recommended
you move Apple programs replaced by
Archive and Install out of the
Applications folder before you Archive and
Install 10.2 over 10.3. This option was
terminated on the release of 10.6.
4. Upgrade Install - Available on upgrade
disks of all versions, as well as retail
disks. This will simply upgrade an
existing X system to a new one, not
concerning itself if any old system
preferencees are incompatible with the new
system. This is usually not the
recommended option because of its lack of
sensitivity to the possibility an old
system may not have compatible parts. It
is however, also the installation which
happens if you select no installation
option. As such, it is recommended you
only do this if you have no non-Apple
applications installed, and all your Apple
applications are up to date.
When you install from the App Store an
operating system that's new and your Mac
supports, that's equivalent to an upgrade
and install.
5. Install Mac OS X for the first time.
When you install Mac OS X for the first
time, it will happen when your machine
never had Mac OS X installed before, or
you erased the drive manually with a hard
drive formatter and it detects there is no
Mac OS X on the system to be installed.
Naturally, if there was a system already
installed on your computer that was
pre-Mac OS X version of the Mac operating
system, it won't touch that system if the
hard drive is in good shape. Be sure of
course to follow the migration tips on Migrating from
Mac OS 9 to X FAQ before doing this.
To continue learning how to do an update
of Mac OS X, please see the Upgrade FAQ.
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