Photoshop CS6 only installs a 64-bit version on Mac OS.
Photoshop CS5 installs a version that can launch in either 32 bit or 64 bit when you install on a 64-bit version of Mac OS (Mac OS X 10.5 or greater). If you are using Mac OS X 10.4 or earlier, then Photoshop only installs the 32-bit version.
Photoshop CS4 installs a 32-bit version only.
Photoshop CS5 on Mac OS installs one copy of the application, and it launches by default in 64-bit mode. You can run Photoshop CS5 in 32-bit mode.
To run Photoshop CS5 in 32-bit mode:
- Quit Photoshop CS5.
- Navigate to Applications/Adobe Photoshop CS5 folder.
- Select the Adobe Photoshop CS5.app file.
- Choose File > Get Info.
- Select Open in 32 Bit Mode.
- Close the Get Info dialog box.
- Reopen Photoshop CS5.
Third-party plug-ins for 32-bit versions of Photoshop don't appear under the Filter menu when you run the 64-bit version of Photoshop. If it's necessary to use plug-ins that haven't been updated, run the 32-bit version of Photoshop. When you are done using the plug-ins, close the 32-bit version. Then, run the 64-bit version. Contact the plug-in manufacturer for information about any updates.
Although the 64-bit version of Photoshop speeds up some operations, it doesn't speed all of them. And, it doesn't speed the operation equally. Generally, operations run approximately 8-12% faster. Overall, processor speed is not the main advantage of using the 64-bit version, except when you run actions on large files. Photoshop writes data to the hard disk incrementally while you pause in Photoshop. When you run actions, there are no pauses for Photoshop to write to the disk. Therefore, Photoshop writes to the disk while the action runs. The increase in processor speed increases these processes.
The primary advantage of using the 64-bit version of Photoshop CS5 is to access amounts of RAM beyond what Photoshop can access as a 32-bit application. Photoshop can take the best advantage of more than 4 GB of RAM only it runs as a 64-bit application. If you use files that need more than 4 GB of RAM, and you have enough RAM, all processing you perform on large images can be done in RAM. It's not necessary for Photoshop to swap out to the hard disk. Unlike on Windows, all supported versions of Mac OS can run Photoshop CS5 in 64-bit mode. When running in 64-bit mode, Photoshop CS5 uses all the RAM you can fit into your computer.
Photoshop CS5 and CS4 install a 32-bit and a 64-bit version when you install on a 64-bit version of Windows 7, Vista, and XP. If you are using the 32-bit version of Windows, then Photoshop only installs the 32-bit version. Photoshop CS6 allows you to choose one or both of these versions to install.
If you are running Windows Vista, upgrade to Service Pack 1 for better performance.
Note: 64-bit Photoshop CS4 was not thoroughly tested under Windows XP64. Although it is not supported, it should run.
Photoshop installs a 32-bit and a 64-bit shortcut into the Start Menu. If it's necessary to manually run the application, the 32-bit version is the photoshop.exe file. It's in the Program Files (x86)/Adobe/Adobe Photoshop CS4 folder. The 64-bit version is the photoshop.exe file in the Program Files/Adobe/Adobe Photoshop CS4 folder.
Third-party plug-ins for 32-bit versions of Photoshop don't appear under the Filter menu when you run the 64-bit version of Photoshop. If it's necessary to use plug-ins that haven't been updated, run the 32-bit version of Photoshop. When you are done using the plug-ins, close the 32-bit version. Then, run the 64-bit version. Contact the plug-in manufacturer for information about any updates.
Although the 64-bit version of Photoshop speeds up some operations, it doesn't speed all of them. And, it doesn't speed the operation equally. Generally, operations run approximately 8-12% faster. Overall, processor speed is not the main advantage of using the 64-bit version.
The primary advantage of using the 64-bit version is to access amounts of RAM beyond what Photoshop can access when the 32-bit version is run. You can take advantage of more than 4 GB of RAM only when you are on 64-bit systems, using 64-bit Photoshop. If you use files that require more than 4 GB of RAM, and you have enough RAM, all the processing you perform on your large images can be done in RAM. It's not necessary for Photoshop to swap out to the hard disk.
This table lists the amount of RAM available to Photoshop with the different versions of Windows:
| Photoshop Version | Windows Version | Maximum amount of RAM Photoshop can use |
| 32 bit | 32 bit | 1.7 GB |
| 32 bit | 64 bit | 3.2 GB |
| 64 bit | 64 bit | as much RAM as you can fit into your computer |
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