Photoshop performance depends on three points: CPU performance, amount of RAM, and speed of the hard drive.
Some Photoshop tunes would help for speeding up Photoshop response if lack of resources slows down the work process. It is possible because Photoshop is very large multifunctional application that could be tuned for various purproses. Painting process is very dynamic and needs instantaneous response from PC for real-time work, so, tunes suggested below are oriented on optimization of drawing/painting process. Nevertheless, they could be useful for other purproses.
This is written using Photoshop CS3. In other versions some paths or menu names could be different.

Inner Photoshop Improvement

1. Setting of memory usage

It is recommended on Adobe site to don't set amount of memory more than 75%, but you can try increase it up to 85%, it isn't dangerous for the system. If this value appears to be too high, Photoshop will be closed suddenly while you are working, so setting this value needs some tests before you start to work with it. By default, Photoshop suggests you ideal range for your system, but it automatically sets the lowest value of this range, you can safely raise it up to the upper value.
Go to Edit->Preferences->Performance and set amount of memory you prefer in "Memory Usage" submenu.

2. Setting separate Scratch Disk for Photoshop dump files

While the file is open, Photoshop makes a temporary dump file for work with the cancas. This dump file contains all information about the work file. The dump file grows while the work file is in use, and the bigger is the work file, the bigger is the dump file. So, it needs some space on the hard drive. By default, dump files are stored on the drive where Photoshop is installed. But it is better, to allot separate hard drive or at least separate logical drive for Photoshop dump files only. So they could grow without touching system files or your stuff.
Go to Edit->Preferences->Performance and select proper Scratch Disk in "Scratch Disks" submenu.

3. Modifying History options

Photoshop allows user to have up to 1000 steps in the History, but every step needs space on your hard drive, and work with undos needs memory.
How does History work? Every time you make an action with the canvas, Photoshop writes this action in temporary file and keeps until you make some next steps. If you have 10 History steps, every 11th step overwrites the 10th, the 10th overwrites the 9th and so on. So, the more History steps you have, the more memory is needed for performing this action in time.
Also, there are so-called Snapshots. They are History steps locked from overwriting. These steps are stored in temporary Photoshop file until the work file is open. The more Snapshots the work file has, the more space for storage of them is required.
Go to Edit->Preferences->Performance and set up number of history steps accordingly to resources of your PC.
Then, go to History Palette Options: Open History Palette->Click the icon with three horizontal lines->History Options and uncheck all boxes. If you need to make a Snapshot, you can do this manually by clicking "Create new snapshot" icon on History Palette.

4. Modifying Recent File list

Photoshop will keep 30 files no matter if you selected to show 5 or 25 files, but on slow PC reading and showing of large list on the screen may decrease performance when large file is opened, so decreasing the number of visible files is good idea.
Go to Edit->Preferences->File Handling and set up numbers of recent files accordingly to resources of your PC. You may set number of recent files as "0" to turn the list off, but it doesn't removes your last 30 files, so you can turn it on at any time without loss.

5. Disable Version Cue

If your work doesn't require synchronization with your co-workers, then you don't need Version Cue do be enabled.
Go to Edit->Preferences->File Handling and uncheck "Enable Version Cue" box.

6. Disable Adobe Bridge

Uninstalling of Adobe Bridge is highly unrecommended because it is tightly integrated with Photoshop. But there are some tricks how to prevent it from running.
Go to Edit->Preferences->General and uncheck the box "Automatically launch Bridge".
Next, go to Edit->Preferences->Keyboard Shortcuts, expand "File" menu item, find "Browse" command and delete shortcuts assigned to Bridge. This prevents launch of Bridge by accidentally pressing of these key combinations.
Then, in the same menu window, open the sheet "Menus", expand "File" menu item, find "Browse" command and make it invisible by clicking on the Eye button near the command. This excludes Bridge from File menu and prevents its launch from there by accidentally choosing wrong menu item.
So, you will never see Bridge until you advisedly click "Launch Bridge" icon on the Photoshop toolbar.

7. Disable unused Plug-Ins, Brushes, Workspaces, Presets and How-Tos

By default, Photoshop loads a lot of pre-installed features and keeps them loaded while work process is going no matter are you using them or no. When Photoshop is starting on the slow PC, you may see how long takes the loading of plug-ins, brushes etc. You may even never see these things, but they are loaded and stored in memory anyway. All of them could be disabled if needed.
How to disable unused filters? There is Adobe Photoshop SpeedUp utility, but it disables all filters at once. It just adds "~" to Photoshop Plug-Ins folder. You can do it by hands and apply it not to the whole folder, but to filters you don't need only. Go to C:/.../Adobe Photoshop CS3/->Plug-Ins->Filters and rename files of filters you never use by adding "~" before their names. You can return any filter back at any time by removing "~" from its name. It prevents these filters from loading, and they disappear from Photoshop Filters menu.
Very helpful is disabling of Filter Gallery: go to C:/.../Adobe Photoshop CS3/->Plug-Ins->Filters->Effects and rename [Filter Gallery.8bf].
How to disable How-Tos? Go to C:/.../Adobe Photoshop CS3/->Help and rename [howto.dat] file.
How to disable unused brushes? Go to C:/.../Adobe Photoshop CS3/->Presets->Brushes and rename files of brushes you don't use.
How to disable unused tool presets? Go to C:/.../Adobe Photoshop CS3/->Presets->Tools and rename files of presets you don't use.
How to disable unused Workspaces? Go to C:/.../Adobe Photoshop CS3/->Presets and rename "Workspaces" folder. Note: Photoshop automatically makes new folder named "Workspaces" instead of the folder you renamed, but this new folder is empty and could be deleted when you decide to return workspaces back.
Also, using this tip, you can disable loading of swatches, gradients, styles, curves, and patterns from Photoshop Presets folder.
[!] Do not forget to save your personal sets into different place before renaming Photoshop default folders.

8. Remove unused fonts

Usually, Photoshop optimization tutorials suggest to turn off font previews, but these previews are very handy. It would be better to remove unused fonts from your system and use 20 preferred fonts with previews instead 20 fonts you need among 400 unused fonts without previews.
How to remove fonts? Go to C->Windows->Fonts, select fonts you don't need and move them in some different folder.
[!] Be careful and don't move default system fonts like Arial or Verdana.
However, if you prefer to disable previews, go to Edit->Preferences->Type and uncheck the box "Font Preview Size".

Part II • Part III

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