Increasing memory

Yes, but I find it important to always ask why you want to add RAM. Too many people think throwing RAM at a slow computer is a cure-all. It's not, in spite of the hype from the RAM sellers. Chances are about 95% that you will experience zero improvement by spendin money on RAM.

Most slow Macs suffer from extreme age or slow mechanical hard drives. You have both issues.

There are THREE families of 2009 iMacs: Early; Mid and Late.

• Early and Mid 20 and 24-inch can using up to 8GB RAM.
• Late 2009 21.5-inch iMacs can use up to 16GB RAM.
• Late 2009 27-inch 2009 iMacs max at 16GB RAM if they have a Core 2 Duo processor, and to 32GB if they have an i5 or i7 processor

Again, carefully consider why you want more RAM for a computer that cannot be upgraded high enough even to run modern browsers and web pages.

Yes. The 27" model can utilize up to 32GB of RAM. The 21.5" model - 16 GB and the 20" models - 8GB.

The 27" model is user upgradeable via the small memory door on the back of the unit. The others require disassembly of the unit thru the front screen and is a technician's job. Since the unit is considered obsolete by Apple you'll have to find an Apple Authorized Service Provider to do the job.

If you have the 27" model only get the additional RAM at Crucial.com or OWC (MacSales.com).

Personally, I would put the money towards a new or refurbished iMac from Apple.

NOTE: be aware that additional memory will not improve the boot speed of the iMac nor the launch/opening speed of apps and documents. Additional RAM only permits more efficient processing of documents and more documents open without slowing down performance.

Yes you can, however it is not worth spending a lot of money to upgrade that old of an iMac.

for an Early 2009 model, see > https://eshop.macsales.com/shop/memory/iMac/DDR3_2009

for a Late 2009 model, see > https://eshop.macsales.com/shop/memory/iMac/DDR3_21.5_27