Understanding Activity Monitor

Question

Level 7

20,731 points

Understanding Activity Monitor

In case it matters, the screen shots included with the questions came from this computer:

I had believed that VM is NOT part of real memory (in this case, the 4GB indicated above). However, the Activity Monitor seems to suggest otherwise. When I hover over the Compressed Memory label, I get the following explanatory message that kinda implies that Compressed Memory is Virtual Memory.

Unfortunately, when I go to the bottom of the screen, the summary information contradicts my belief and adds an additional confusing factor. App Memory + Wired Memory + Compressed = Memory Used (approximately).

This computer has 4GB of hardware RAM. IN THIS EXAMPLE, how much of that 4GB is being used? To me, the term "Wired Memory" suggests that that is the figure but "Memory Used" is 2.82G. What is Wired Memory? What is App Memory (with this confusion I'm not about to make an assumption)? What is Compressed Memory? Why is it that App Memory plus Wired Memory plus Compressed does not exactly equal Memory Used?

Going further, is there any way to determine how much of the 4G hardware RAM is being used by the MacOS?

iMac (Retina 4K, 21.5-inch, 2017), macOS High Sierra (10.13.2)

Posted on Feb 7, 2018 1:30 PM

Reply

Answer 1

Top-ranking reply

Tesserax

Level 10

153,174 points

Feb 7, 2018 2:49 PM in response to Philly_Phan

In this example, a total of 6.01 of 8 GB of RAM are being used by applications and processes. Even though you my only have a few apps actually opened, these processes are also culprits for using memory. Of the 6.01 GB, macOS has allocated RAM as it "sees fit" to best accommodate all of these.

Trust me, I have some pretty intense Apple Developer articles, related to macOS memory management, that I'm sure will help you fall asleep better if read.

Unless you are having RAM performance issues on your Macs, I wouldn't worry about it ... and assuming that having the memory pressure indicator in the green is what you want.

The Engineer in me wanted me to provide this links. Enjoy! 😉:

About the Virtual Memory System - Apple Developer
Memory and Virtual Memory - Apple Developer

Reply

Answer 2

Tesserax

Level 10

153,174 points

Feb 7, 2018 2:30 PM in response to Philly_Phan

The Apple Support article that CT provided you a link to pretty much provides Apple's definitions for each of those terms.

In my case, I have a 2014 Mac mini with 16 GB of RAM. A current snapshot of the Memory tab with a number of applications running (Safari, One Note, Mail, SpamSieve running in foreground + others in the background) still didn't require any of that RAM to be assigned to the "Compressed" category. Notice also, that with this much RAM, my mini stays in the "green band" in the Memory Pressure window. You aren't too far off thinking of this memory as akin to VM memory.

To determine how much RAM macOS itself is using, may prove a bit tricky. You already know that the Activity Monitor lists all applications/process that is using memory. To get a close approximation, you would need to quit any application that you are currently running and those that you may have configured to start at boot up.

Reply

Answer 3

Philly_Phan Author

Level 7

20,731 points

Feb 7, 2018 2:28 PM in response to Tesserax

This is getting uglier and uglier. I went to my iMac (8GB RAM). Other than what's running in the background, the only apps that are open are Mail (opens at logon), Safari (so I can post this message) and, of course, Activity Monitor. I get the following:

If the total memory used is significantly less than the physical 8GB, why in the world is there anything in Compressed or Swap? Actually, I have the same question regarding the MBP (see my original image).

I went back to the MBP and opened a complex Photoshop document (Photoshop uses a little less than a full gig). My Compressed figure shot up to accommodate Photoshop BUT the Memory Pressure stayed solid green!

Am I OK in oversimplifying that, if Memory Pressure is all green, I have no memory problems? Yes, I know that VM is slower than real memory but I'm excluding that aspect.

Reply

Answer 4

Philly_Phan Author

Level 7

20,731 points

Feb 7, 2018 3:00 PM in response to Tesserax

Thanks. I think that I'll stop looking for trouble.

When I use Photoshop, nothing else is open except the background apps. Even Mail is shut down (I take photography seriously and I don't want to be disturbed by the dings). Granted, I'd be better off with more RAM but the biggest RAM hog that I have is Photoshop and it runs just dandy. Besides, I just learned that Memory Pressure remains solid green.

Thanks again for your help.

Here are some pics that I took of Buzz Aldrin last year. Like I said, I take photography seriously.

Reply

Answer 5

John Galt

Level 10

147,810 points

Feb 7, 2018 8:11 PM in response to Philly_Phan

Those are some outstanding photos of an outstanding American Philly_Phan.

Perhaps you can help this guy?

Preview - reviewing and then deleting

A question about Preview, is it possible to view a jpeg and then whilst still within the Preview application delete the jpeg and move to to the next jpeg in the folder? I can do this easily in Windows, but not so in macOS 10.13.3.

I don't think Preview is appropriate for what he wants to do.

I think that I'll stop looking for trouble.

Please don't 🙂

Reply

Answer 6

Philly_Phan Author

Level 7

20,731 points

Feb 7, 2018 1:49 PM in response to CT

I read that previously and it's clear as mud (and it doesn't even cover ground). Is Compressed Memory and Virtual Memory the same thing?

According to the definitions there, App Memory should be part of Wired and Compressed and the total of the two should equal "Memory Used" and that's clearly not so. Further, if it's NOT included in Wired and/or Compressed, then the total of the three should equal "Memory Used" and, although close, it doesn't quite add up. Further, further, if Compressed Memory IS the same as Virtual Memory, then that should be excluded in the "Memory Used" entry.

The link gives absolutely no information regarding the memory used by the MacOS.

Reply

Answer 7

Philly_Phan Author

Level 7

20,731 points

Feb 7, 2018 1:57 PM in response to Tesserax

I was afraid of this. Your response actually triggered another question, this time a much more serious question than my earlier ones! Take a look at my image. My Memory Pressure is also solid green. Why then am I using Compressed Memory?

Reply

Answer 8

Tesserax

Level 10

153,174 points

Feb 7, 2018 2:29 PM in response to Philly_Phan

It may be possible certain apps (or processes) that you are running have greater memory allocation demands. I suggest that you review your Activity Monitor's Memory tab and see which apps or process required compressed memory. This may root out some culprits to take a closer look at.

With today's apps, what seemed an appropriate amount of RAM when you purchased your Mac, maybe totally inadequate now.

Reply