Information Technology Reference
In-Depth Information
11.4 You can use Activity Monitor's System Memory tab to track how MacBook Air is using memory.
The pie chart shows how MacBook Air is currently allocating your computer's RAM. The total amount of
RAM available appears below the pie chart. These four types of RAM appear:
Free. This is the number of megabytes currently available for processes. As this number gets lower, system
performance slows because MacBook Air may reduce the memory that each process uses. If this number (plus
the Inactive number, described in this section) drops very low (a few megabytes), use the Activity Monitor to
see if a process is using excessive amounts of memory.
Wired. This is the number of megabytes that must stay in RAM and can't be stored on disk in virtual
memory.
Active. This is the number of megabytes currently stored in RAM and used by processes.
Inactive. This is the number of megabytes currently stored in RAM and no longer used by processes. All
this data has also been paged out to virtual memory, so the RAM is available for another process to use.
Besides these four types of RAM, the System Memory tab also displays five other values:
Used. This is the total amount of information currently being stored in RAM. It's the sum of the Wired, Act-
ive, and Inactive values.
VM size. This is the size, in gigabytes, of the virtual memory cache on the hard drive.
Page ins. This is the amount of data that the system has read in from virtual memory. If this number grows
quite large, it means MacBook Air's performance is not what it could be because the system must retrieve data
from the relatively slow hard drive. You need to shut down some running programs or processes.
Page outs. This is the amount of data that the system has had to write to the hard drive's virtual memory to
free up real memory. This value is likely 0 most of the time, but it's okay if it's not. However, if it starts to get
large (hundreds of megabytes) in a short time, it likely means that your system doesn't have enough real
memory for the programs you're running.
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