Hi, are there any computer geeks out there who could tell me how to speed up my slowing (6-year-old) iMac?

Buy a new one 

https://www.macworld.co.uk/how-to/mac/how-to-speed-up-slow-mac-3636548/

Mike

I just knew that some bright spark would come up with that solution  ; unfortunately, I don't have a spare ?1200 ? or whatever ? lying around.

Try the link then...

Thank you, mikem.

Inevitably most sorts of computers slow with time. Do the usual " housekeeping " by clearing the cache. cookies etc each week with a tool like CCleaner ( this may also delete logins you have saved so make a note of passwords.) It seems that most computer experts recommend a defrag now and then. ( assembles the data more in order on a hard disc. ) You might try a Registry clean up but some experts are wary of recommending it. Also check the Start Up as there may be too many programmes trying to get loaded. Ultimately the other answers are right. At 6 years old this sort of technology is well past its best. My six year old desktop was slowing down and getting annoying. I bought a new HP desktop at ?500 and the Start Up is ten times faster. Basically this is because Windows loads across both dual core processors . As for running through pages you will find that some Browsers run quicker than others. A recent artical in " Web User "( see also website ) put most to the test to see which was quickest . The new " Firefox Quantum " is quick but lacks certain capabilities like downloading Google Earth and viewing photobooks in " Photobox ".In the case of browsers like the hardware itself the less complex or more stripped down it is the quicker it will run.

The best possible upgrade is to replace the hard drive with an ssd if it doesn't already have one (not sure how easy it is to do on imacs though) 

You have to see if the iMac can be upgraded, a lot of the more recent ones can't be.  Assuming it can be an SSD will give a performance boost or you can add a larger normal hard drive.  Make sure you get one with enough storage space and allow a good margin.  You can also upgrade the RAM if you have 4GB or less then an upgrade to 8 or 16 is a good idea.  Crucial are a good company here.
You will also need to migrate your data.  First back it up using time machine and also another back up of important docs, pictures is a good idea.  When I upgraded my 2012 MacbookPro I used a bit of software called Carbon Copy Cloner.  You need to get a UAB to SATA lead, plug the new drive in to this and one of the USB ports and it will exactly clone your current drive.  Then swap them over.  It's actually quite easy, just takes a bit of time for the data transfer.  I didn't get an SSD this time round I just upgraded the old 500GB to a 1TB as running out of space and the RAM from 4 GB to 16GB.  Works fine.
A bit of housekeeping might help as well, move stuff off the desktop, empty trash etc. plenty of stuff to google on this.

Thanks for all your suggestions. I'll investigate them as soos as I can.

You might need a new keyboard as your letters are malfunctioning.

I wouldn't touch "PC cleaner" programs with a barge pole, especially if they fiddle with the registry. That's a great way to make your computer unstable.

Learn how to see what programs and services are running automatically in the background / on startup. Many of them are unnecessary and can be stopped. Only stop a program from loading if you know what it does (Google).

SSDs can be a nice upgrade, but can also be completely useless. If you are hamstrung by memory not I/O, then adding an SSD is not going to help. Try to find out what part of your system is the bottleneck. There should be a task manager program that can show resource usage (I'm not that familiar with Macs).

Mike Hopley said:

I wouldn't touch "PC cleaner" programs with a barge pole, especially if they fiddle with the registry. That's a great way to make your computer unstable.

(I'm not that familiar with Macs).

Click to expand...

The Mac OS is Unix-based, so it hasn't got a registry. Which is why it's not so susceptible to viruses.

tony from suffolk said:

Which is why it's not so susceptible to viruses.

Click to expand...

It's less susceptible to viruses because more viruses are written to target the most popular operating system, Windows. As Macs became more popular, viruses have become somewhat more of an issue.

Macs do have a sort-of equivalent to the registry, as naturally they need to store the same kind of information somewhere.

Mike Hopley said:

tony from suffolk said:

Which is why it's not so susceptible to viruses.

Click to expand...

It's less susceptible to viruses because more viruses are written to target the most popular operating system, Windows. As Macs became more popular, viruses have become somewhat more of an issue.

Macs do have a sort-of equivalent to the registry, as naturally they need to store the same kind of information somewhere.

Click to expand...

Well the fact is, it's easier to write viruses to infect Windows because the registry is contained in one place, whereas the equivalent Mac instructions are held in seperate locations.