Beachballs galore on iMac, but very few on MBP?

Hello all -

First, I really appreciate the level of expertise on this forum. It's become my go-to place to find answers. I've only been a Mac user since 2008, so I still have a lot to learn.

I have two Macs, an iMac and a MacBook Pro. After installing Yosemite, I've been getting a horrendous amount of beachballs (and all that comes with them) on the iMac, but very few on the MBP. As I type this (on the MBP...), the iMac is backing up in prep for a clean (re)install of Yosemite. After much research here and other places, I think it will solve my problems. Hopefully.

My question to y'all is... why the beachballs on the bigger, more powerful machine, when the smaller, less powerful one is fine? It's my understanding that just updating with each new release is what causes this, but I've never done a clean install on either machine. They both have about the same number of apps. I guess I'm just curious. Specs below.

iMac, Mid 2010
OS X Yosemite 10.10.1
2.93 GHz Intel Core i7
8 GB 1333 MHz DDR3
1 TB HD (lottttttts of free space...)

MBP, Early 2008
OS X Yosemite 10.10
2.5 GHz Intel Core 2 Duo
4 GB 667 MHz DDR2 SDRAM
200 GB HD (notttt much free space...)

Thanks in advance. Cheers.

Suggest you do a clean install of Yosemite. Think dtravis7 got his post a little mixed, but they do that in Ca.

The original question was:

".. why the beachballs on the bigger, more powerful machine, when the smaller, less powerful one is fine?"

So it appears 4GB and a fuller disk is sufficient on the older MBP.

Trying a clean install again sounds sensible.

4GB is not enough for Yosemite no matter what apple says.

I am running Yosemite on my MB Air, 13", i5, 4GB memory, 250 SSD. It runs it fast and extremely well. If I get a beachball it is short lived. I did an upgrade over Mavericks. Other than the initial mail issues, I have had no problems. I attribute the outstanding performance to the very fast SSD and Haswell. The 4GB of memory has not been an issue.

I also have a MB Pro, 2011, 16GB of Memory, 1TB hard drive. I also upgraded it to Yosemite. It runs it well but as far as which laptop is the snappiest the Air smokes the Pro. Why? The SSD and Haswell.

I will say memory intensive programs like Premiere Pro I would not attempt on the Air as here memory does matter.

Obviously both Mavericks and Yosemite handle the memory it has to work with. I keep reading about the need for 8GB for Yosemite and I don't disagree but a lot depends on the internal architecture (Haswell versus Ivy Bridge) and mechanical hard drives versus solid state drives.

BTW: I have a white Macbook, 2009, Core2Duo, 4GB of memory, 160GB Hard drive running Yosemite (clean install) I use it to run Premiere Pro for capturing live video. I have had it capturing while cruising on the internet. Very acceptable performance.

I believe if all the hardware is functioning correctly and there are no corrupt/bad driver issues OS X runs great. If there are corrupt/bad drivers or a weak piece of hardware, OS X has issues regardless of which version.

Lisa

The iMac with 8GB is having the problems, not the MBP with 4GB. If things continue consider the clean install.