Mac Activity Monitor
The Activity Monitor is a free system utility that comes on all Macs. It includes tabs for five areas that illustrate how applications and other processes affect your computer. The tabs are:
CPU: Shows the effects of processes on CPU activity Memory: Monitors usage of memory including the RAM physical memory Energy: Indicates the amount of energy used by each app Disk: Shows the amount of data read from and written to the disk Network Usage: Indicates which processes are sending or receiving data over your network
The Memory tab of Activity Monitor is where you monitor and manage memory usage on your Mac.
Activity Monitor Memory Chart (OS X Mavericks and Later)
When Apple released OS X Mavericks, it introduced the Memory Pressure chart in Activity Monitor, along with compressed memory, a significant change in how the operating system manages memory. Memory compression makes the most of available RAM by compressing the data stored in RAM instead of paging memory to virtual memory, a process that can significantly slow down the performance of a Mac. In addition to the use of compressed memory, Mavericks brought changes to Activity Monitor and how it presents memory usage information. Instead of using the pie chart that appeared in earlier versions of OS X to show how memory is divided, Apple introduced the Memory Pressure chart as a way to express how much memory your Mac compresses to provide free space for other activities.
Memory Pressure Chart
The Memory Pressure chart appears at the bottom of the Memory tab in the Activity Monitor window. It indicates the amount of compression being applied to RAM, as well as when paging to disk occurs when compression isn’t sufficient to meet the demand by apps to allocate memory. The Memory Pressure chart displays in three colors:
Green: Indicates no compressionYellow: Shows when compression is occurringRed: Compression has reached its limits, and paging to virtual memory has started
In addition to the color that indicates what’s occurring within the memory management system, the height of the bars reflects the extent of compression or paging that is ongoing. Ideally, the Memory Pressure chart should remain in the green, indicating that no compression is occurring and that you have adequate available RAM for the tasks that need to be performed. When the chart begins to show yellow, it indicates that cached files that are no longer active but still have their data stored in RAM are being compressed to create enough free RAM to assign to the apps requesting an allocation of RAM. The memory compression requires some CPU overhead, but this small performance hit is minor and usually not noticeable to the user. When the Memory Pressure chart begins to display in red, there’s no longer enough inactive RAM to compress, and swapping to disk (virtual memory) is taking place. Swapping data out of RAM is a much more process-intensive task and is usually noticeable as an overall slowdown in your Mac’s performance.
How to Tell When You Need RAM
The Memory Pressure chart makes it easyto tell at a glance if your Mac needs additional RAM.
If the chart is green most of the time, your Mac doesn’t need additional RAM.If your chart is a mix yellow and green, your Mac is making the best use of the available RAM without having to page data to the drive. You’re seeing the benefit of memory compression and the Mac’s ability to use RAM economically to keep you from having to add more RAM. If the chart is usually yellow and seldom green, you may need RAM in the near future.If the chart is in the red frequently or for an extended time, your Mac would benefit from more RAM. If it only peaks into red when you open an app but otherwise stays in yellow or green, you probably don’t need more RAM, although you may want to cut back on how many apps you keep open at the same time.
Activity Monitor Memory Chart (OS X Mountain Lion and Earlier)
Earlier versions of OS X before OS X Mountain Lion used an older style of memory management that doesn’t make use of memory compression. Instead, it tries to free up memory that it previously allocated to apps, and then—if needed—to page memory to your drive as virtual memory.
Activity Monitor Pie Chart
The Activity Monitor pie chart shows four types of memory usage: Free (green), Wired (red), Active (yellow), and Inactive (blue). To understand memory usage, you need to know what each memory type is and how it affects available memory.
Free. This is the RAM in your Mac that it isn’t currently using and can assigned to any process or application that needs all or some portion of the available memory.Wired. Your Mac assigns Wired memory to its internal needs and the core needs of applications and processes you’re running. Wired memory represents the minimum amount of RAM your Mac needs at any point in time to keep running. You can think of this as memory that’s off-limits for everything else.Active. Memory currently in use by applications and processes on your Mac, other than the special system processes assigned to Wired memory, is Active memory. You can see the Active memory footprint grow as you launch applications or as currently running applications need and grab more memory to perform a task.Inactive. Inactive memory is no longer required by an application but the Mac hasn’t yet released to the Free memory pool.
Understanding Inactive Memory
Most of the memory types are straightforward. The one that trips up people is Inactive memory. Individuals often see a large amount of blue in the memory pie chart and think their Mac has memory issues. This leads them to think about adding RAM to boost their computer’s performance, but in reality, Inactive memory performs a valuable service that makes your Mac snappier.
What Is Inactive Memory?
When you quit an application, OS X doesn’t free all the memory the application used. Instead, it saves the application’s startup state in the Inactive memory section. Should you relaunch the same application, OS X knows it doesn’t need to load the application from your hard drive because it’s already stored in Inactive memory. As a result, OS X redefines the section of Inactive memory that contains the application as Active memory, which makes relaunching an application a quick process.
How Does Inactive Memory Work?
Inactive memory doesn’t remain inactive forever. OS X could start using that memory when you relaunch an application. It also uses Inactive memory if there’s not enough Free memory for an application’s needs. The sequence of events goes something like this:
When you launch an application, OS X checks to see if it’s stored in Inactive memory. If it is, that memory is reassigned as Active and the application launches.If the application isn’t in Inactive memory, OS X carves out an appropriate chunk of Free memory for the application.If there isn’t enough Free memory, OS X releases some Inactive memory to fill the application’s needs. Releasing Inactive memory removes one or more of the cached applications from the Inactive memory pool, forcing a longer launch time for those applications.
So, How Much RAM Do You Need?
The answer to that question is usually a reflection of the amount of RAM your version of OS X needs, the type of applications you use, and how many applications you run concurrently. However, there are other considerations. In an ideal world, it would be nice if you didn’t have to raid Inactive RAM often. This provides the best performance when launching applications repeatedly while maintaining enough Free memory to meet the needs of any currently running applications. For example, each time you open an image or create a new document, the related application needs additional Free memory. To help you decide if you need more RAM, use Activity Monitor to watch your RAM usage. If Free memory falls to the point where Inactive memory is being released, you may want to add more RAM to maintain maximum performance. You can also look at the Page outs value at the bottom of Activity Monitor’s main window. This number indicates how many times your Mac has run out of available memory and used your hard drive as virtual RAM. This number should be less than 1000 during a full day’s use of your Mac. You don’t need to add more RAM if your Mac is performing to your expectations and needs.
