Should I upgrade my late 2009 27" iMac from Yosemite to High Sierra?

Presumably you have some vintage applications from third-party makers

that may need upgrade or purchase of later versions to continue their use.

Some may or may not have been carried forward, so to look to their makers

sites to see if they have been, before upgrading to a fully newer level of OS

is a fair idea. From Yosemite you may choose to try El Capitan 10.11.6, and

you could try Sierra 10.12.x ~ because there are support pages with links.

According to what I see in these, your iMac 27-inch Late 2009 model could

use any of them; but your other-party software may need purchase upgrade.

And in any event, you should upgrade RAM with correct grade & type chips.

Enter your model build info & see examples of Mac upgrades: MY UPGRADES

And if the Hard Drive requires attention (or optical drive) they offer good choices.

OWC DIY Drive Upgrade/Install Kits for Apple iMac Models

(To upgrade more than RAM, study instructions & videos (owc/ifixit) for details.

These may require a skilled Apple trained service provider, and ask if they can

help, if you chose to get parts elsewhere; as some won't use ones you bought.)

About El Capitan 10.11.6:

How to download OS X El Capitan - Apple Support

About Sierra 10.12.x :

How to download macOS Sierra - Apple Support

About High Sierra 10.13.x :

How to download macOS High Sierra - Apple Support

The 27-inch Late 2009 iMac would love for you to upgrade the RAM to as

much as it could use; any Mac OS X or macOS would appreciate more RAM.

See how to add or remove memory chips in iMac:

• Install memory in an iMac - Apple Support

iMac 27-inch (Late 2009) information:

{from MacTracker spec database}

Introduced October 2009

Discontinued July 2010

Model Identifier iMac10,1 (Core 2 Duo) -or- iMac11,1 (Core i5, i7)

Model Number A1312

EMC 2309 (Core 2 Duo) -or- EMC 2374 (Core i5, i7)

Order Number MB952LL/A (3.06 GHz), -or- MB953LL/A (2.66 GHz)

Locate your 'build year model' 27-inch iMac (Late 2009) from among these:

iMac Intel 27" Repair - iFixit

{Note the EMC number as it relates to using guides such as iFixit and

also to detail what you have. An other method would be to use serial

number lookup site for your information only, to see exactly when your

Mac was built, where, and what its configuration had at that time.}

Mac Serial Number info - Lookup your Apple Serial Number (don't post here)

https://www.powerbookmedic.com/identify-mac-serial.php

You could probably DIY that with instructions from Apple or iFixit guides. And

the upgrade RAM from crucial.com or owc/macsales usually are top-notch.

As both of these providers have guaranteed product, OWC tests in actual Mac

per each category; so if you know and order what it needs, they guarantee it.

Maximum Memory 32 GB (Core i5 or Core i7 Actual) 16 GB (Apple)

Memory Slots 4 - 204-pin PC3-8500 (1066 MHz) DDR3 SO-DIMM

{An older Mac may be needing a replacement hard drive or upgrade to higher

capacity; some are better suited. Others not so much. OWC page does tell of

those which may need an additional 'sensor kit' or special cables to the fans

do not run excessively. This happens when an upgrade or replacement HDD

has no built-in sensor for heat and fan control, while original one did. So there

is a work-around that satisfies the hardware requirement for a working sensor.}

Hopefully you can have more good years ahead with your iMac 27-inch model...

But you may wish to read up on what may be weak points, now there's a history.

The small partition you created for High Sierra may be OK for test purposes;

however even modern memory management in these later macOS versions

is not capable of creating useful virtual memory out of thin air or less than

adequate unused storage capacity; a RAM chip upgrade is recommended &

And maybe larger internal HD, an SSD would be a rocket-performance boost.

Matching RAM pairs: Your Late 2009 iMac 27-in. model has upgrade potential

that's suggested and documented, in sources elsewhere via linked data sites.

~ Happy upgrades!😝

Should you be able to acquire at least 4GB more (depending on vacant RAM upgrade slots; empty number)

for a total of at least 8 GB you may be able to locate what may be considered by some as a threshold least

amount of memory RAM to run the macOS and some less hungry applications.

There are a few resellers one who says they have OWC parts in AU; however there's an import duty and tax

plus shipping on most everything. Maybe even a value-added tax, or if someone in bureaucracy considered

all RAM is the same, they may even have a tax to allegedly lessen the loss to some local supplier to imports.

From the everymac.com site, there are some suppliers located in various regions; none there for SA, while

those in Australia suggest for a price they can ship. Memory chips are relatively light and with robust packing

could not weigh in at 16oz or half kilo in sturdy box. ~ While they can offer quote they may say no. The two

listed do have memory chips for your model.

For one noted reseller in AU macfixit.au info page and contact details to ask. And prices are in AU$.

https://www.macfixit.com.au/apple-memory-ram/

https://support.macfixit.com.au/article/7-shipping-charges-delivery-times

Another AU source ramcity/au offers product, didn't look into shipping page:

RAM & SSD Upgrades | Apple iMac 2009 (Late) Core 2 Duo 3.06 GHz 27-inch (iMac10,1)

You may also contact crucial.com to inquire by email if they suggest a licensed reseller of their memory in

S.A. - if their guarantee has a local replacement source. owc macsales.com, has good info services, too.

Going direct to these noted mac-centric suppliers may be helpful to locate credible regional sources.

{My Mac mini i7 Late 2012 2.3GHz (quad/server) with dual 1-TB rotational HDs (5400-RPM) is OK with an

upgrade to 16GB RAM. Settled on OWC because they had information. The crucial brand is sold through

several official sources (I asked directly, and had them validate part numbers for different inventory that

had correct technical specs; they were different stock numbers, but crucial said they would work) but in

the end for a few dollars more at the time, esales/owc offered less risk with specific part numbers.}

The Mini Mac shipped with 4GB RAM in two chips; with only two slots of 1600MHz memory, I got 2+ 8GB.

Your older model iMac uses the slower MHz memory of different configuration per the specs already noted.

And my Mac Mini included Mavericks 10.9.0, updated online to 10.9.5 & updated included applications, too.

Didn't get Yosemite then it went offline, got El Capitan before it was taken down from the Mac App Store;

and last year I finally upgraded Mini to Mac OS X 10.11.6. As I'd already upgraded 16GB RAM, it was set.

Before El Capitan disappeared (then returned) I downloaded installer. A year later, I installed it. ~ And kept

Mavericks 10.9.5 on separate 500GB partition in HD #1; the second HD #2 is still empty. This dual boots.

The original server edition Mavericks 10.9(.5) and original included applications plus complete El Capitan.

Anyway, you may be able to get less than full upgrade RAM total and have it work; until you afford the max.

Good luck & happy computing! 🙂

The models were either two or four core, the one he has was identified here

and what they said I copied from MacTracker. While I supplied a link to OWC

MY UPGRADES that would carry information up dated from back in 2009... I

did not look into all of it for clarity or fitness of purpose. But I did see what was

said - and copied it from MacTracker v. 7.4.1 - as seen in my Mac OS X 10.5.8.

So in good faith and from the databases both in local archive and online

(links tested) I provided quite a bit and also means to cross-check data.

•iMac Intel 27" EMC 2309 and 2374 - iFixit

•iMac (27-inch, Late 2009) - (RAM) Apple Support

..Good luck & happy computing..😐

PS:

Although you could choose to ask an official Apple presence in S.A.

for cost and availability of upgrade RAM memory chips for your iMac

the pricing may be higher than some other sources, if available.

Considering import duties and other non-specified added costs above

shipping, to know the baseline price via an official Apple source is good.

• Not sure if this support contact is still good; I moused-over to read URL:

Official Apple Support - oh, South Africa (link automatically changed to text)

Apple ~ South Africa:

South Africa
0800 444 426¹

• Contact Us
• Phone Numbers
• My Support

The OP has the exact same Core2Duo, 27 inch screen, 2009 iMac as I.

The dual core models can only take a maximum of 16 GBs of RAM.

I recommend the OP install the full 16 GBs of RAM from crucial.com or OWC ( macsales.com ) in his late 2009 iMac model.