Updates to Files On-Demand on macOS

Gregleleu most or all modern operating systems use virtual memory, which uses a combination of disk storage and a RAM cache to simulate more RAM than is physically present. Programs can read and write to what looks like a huge chunk of RAM, but behind the scenes the OS is keeping the most recently and often accessed data in RAM and offloading the less accessed data to disk. This is particularly helpful when “parking” background processes, which frees up physical RAM for foreground processes that are actually executing. You can see the effects of this when switching between programs on a RAM starved machine, as there is a pause while the OS stores one program’s working memory to disk and pulls the other’s into physical RAM. This is also one reason why solid state drives can make a low RAM computer run so much faster than with spinning disks—virtual RAM swaps happen roughly ten times faster, so you don’t have to wait nearly so long for programs or program modules to load and unload.