Mac slow, spinning wheel

[richwhite08]

I have a MBP, mid 2012 but purchased last year, that is being very slow. Generally runs fine but opening things is slow, even system preferences, and it frequently has spinning wheel

It has 10gb ram, an 8gb and 2gb sticks. It was like it on Yosemite and is still like it on El Capitan, even with just a few things open. Any way to diagnose it?

 

[richwhite08]

Update: it got like this when kernel task got to be large and a reboot fixed it. Kernel task is currently at 900mb, which is higher than normal. Why would that be?

 

[richwhite08]

Update: failed hard disk! Three weeks left on the warranty so should be a simple replacement

 

[ApolloBoy]

Perfect time to stick an SSD in there if you ask me. An SSD will make your cMBP both more reliable and much faster compared to a standard hard drive.