Macbook pro mid 2012 slow down I'm actually asking about my wife's MacBook Pro which I don't use very often. It's slowed down quite a bit recently and apparently before the update to El Capitan. Programs have started to take a long time to launch but once they have launched actually run fine. After booting up it will take about 45 seconds for Safari to even be usable. Spotlight also lags a lot and can't even keep up with typing, although it responds to 'escape' quickly.

I've watched the system monitor and even when programs are launching the CPU seems to be low with around 90% idle. It has 4GB of RAM and there always seems to be around 1.5Gb free.

I've attached the summary showing the hardware below. It doesn't have an SSD.

I've also run the Apple Hardware Test which took approximately an hour and nothing was reported from it.

From what I've read people have suggested upgrading the memory but since it doesn't seem to be running out of memory I would be surprised if this helped. There's also very little running and nothing user installed that is being launched in the Dock at start up. 

Any help would be great and happy to provide any other stats needed. 

Model Name:    MacBook Pro


Model Identifier:    MacBookPro9,2
Processor Name:  Intel Core i5
Processor Speed: 2.5 GHz
Number of Processors:    1
Total Number of Cores:   2
L2 Cache (per Core): 256 KB
L3 Cache:    3 MB
Memory:   4 GB
Starting with OS X 10.9 it appears that OS X relies heavily on one having an SSD.  Since apps, which have been run once after startup, when relaunching them, they are mainly started off inactive memory/cache and therefore are faster the second time you start them.  This is in line with your statement that once they are loaded, they work fine.

As a comparison, in my Mac Pro (Early 2008), I used conventional HDDs for a very long time as well.  The computer originally came with Mac OS X 10.5 Leopard, which purred on this machine.  All following big cats also purred away without a problem at all.

However, with the naming convention change of OS X 10.9 Mavericks, loading something from the HDD became cumbersome along with it (tested with System Preferences which took 30(!) seconds to show up after the system was started).  Once started and closed, it re-opened fast (due to it still being in inactive memory or cache).

The same could be seen later with "Star Wars: The Old Republic" under Windows on the very same computer.  Using the HDD it took some time to load the game and/or planets.

While you can try things like clearing caches (which you can find at ~/Library/Caches), or back up all your data (e.g. using Time Machine) and reinstall OS X entirely (to verify that upgrading to newer OSs did not leave undesired settings), for the long haul I guess that you will not get around spending a bit more and get an SDD.  I did so myself eventually.

While dissatisfied to spend money as well, I am very satisfied with the results.

IMPORTANT: If you buy a non-Apple SSD drive, you want to check about trim to optimize it.  Otherwise you may wear it down too fast and spend even more money in buying a new one earlier.