increase speed?

1- Add more RAM

http://store.apple.com/us/browse/home/shop_mac/mac_accessories/memory?mco=MTM3Nj k4ODc

2- Install Snow Leopard

http://www.apple.com/macosx/technology/

3- Run iDefrag

http://www.coriolis-systems.com/iDefrag.php

Since there were several different 2.4 GHz models, you can either check this site or post your model identifier (in System Profiler) so we can figure out which and how much RAM you can upgrade to:

http://www.everymac.com/systems/apple/imac/index-imac.html

Once we figure that out, the RAM vendors usually recommended here are either OWC (macsales.com) or Crucial. You do not need to buy the RAM from Apple; you can save significantly by buying from one of the two mentioned and both are reputable and offer lifetime warranties.

SL states that it needs a minimum of 1 GB RAM; from my experience, a minimum of 2 GB is better. After that, it depends on what type of use your Mac gets as to how much RAM you want to add (depending on how much your model will allow).

I would not recommend running iDefrag; those types of apps are unnecessary on a Mac. The Mac OS does this on the fly with any file smaller than 20 MB; unless you are heavily into editing/working with large video files continuously, there is no need to defrag. If you do at some point run into a directory file problem, then Disk Warrior would be the app of choice.

Make sure you empty the trash. Make sure you empty iPhoto trash, too.

- Delete old files you no longer need.

- Make sure background tasks are not running (activity monitor)

- Download CleanMyMac http://macpaw.com/

- Keep at least 10 GB free on the computer.

- Quit applications when not being used.

- Unplug mouse, keyboard, Harddrives etc when not being used.

Unplug mouse, keyboard, Harddrives etc when not being used.

This is absurd. If the Mac isn't being used, then speed isn't an issue, is it? How would disconnecting the mouse and KB improve speed, anyway, even if it were possible to use the computer in that state? And if an external drive is unmounted and powered down, how exactly will that speed anything up? I've never seen any slowdowns from a mounted, powered on drive.

A program like CleanMyMac will only be useful in speeding things up if you allow the drive to get extremely low on disk space. It also runs a number of other things, like cache cleaning, that will not only not speed up your Mac, it will slow things down as caches are being rebuilt from scratch. Cache cleaning should be used judiciously only for troubleshooting. Removing localizations and apps and related files will, generally, not have much of an effect on disk space.

I don't trust all purpose programs like this. It doesn't come free and many of its features can be run manually by anyone who wants to invest a half hour of time learning some pretty basic things. Just go into the Home Folder and remove bloated, unneeded files there. This is usually where most wasted disk space will be. In addition, there are free maintenance programs that can do the job quite well. But you must still be careful using them.

OmniDisk Sweeper (to see where space is being used.)

For maintenance:

Applejack

Onyx

You beat me to it.....

Add: 10 GB is not necessarily enough to improve performance; a minimum of 10 - 15% of total hard drive capacity is recommended for the OS to operate properly.

Some background tasks need to run or the computer will not (kernel_task comes to mind).

Don't DEFRAG your hard drive!!!

iMac 27", 3.4GHz Quad-Core Intel Core i7, 16GB 1333MHz DDR3, 2TB HD + 256GB SSD, AMD Radeon HD 6970M 2GB GDDR5•FCS 3•OS X 10.6.7•iPad 1&2•Apple Tv 2

When on a laptop, for example, extra hard drives that are connected drain battery. As do things like Apple's Magic Mouse and Wireless Keyboard.

And depending on how many drives you could have connected...

Just giving opinion. Works for me.

The OP asked about increasing the speed on an iMac, not a laptop. There is no battery drain on an iMac.

Touché.