Is cached memory bad on a Mac?
No. Cached Files is memory macOS uses to hold files you opened recently so they open faster next time. When an app needs the space, macOS takes it back. A Mac with almost no free RAM is normal. Real trouble looks different: swap that keeps growing, and a memory pressure graph that stays yellow or red.
What Cached Files is
In the Memory tab of Activity Monitor, Apple describes Cached Files as files cached by the system in unused memory to improve performance. Open a large project folder, a video or a big app once, and macOS keeps what it read. The second time it comes from RAM instead of the disk.
That is a good use of memory that would otherwise do nothing. Unused RAM does not save power or speed anything up, so macOS fills it with something that might help.
Why free memory is almost always near zero
This is by design. Over a working day the cache grows to fill whatever is not in use. If you run vm_stat you will see a small Pages free number on a healthy Mac, and that is expected. Activity Monitor does not even lead with a free figure. It shows Memory Used and Cached Files as separate figures.
Some third party tools lump cached files into "used" or draw a nearly full bar in red. That reads as a problem when it is not one. If a tool says your memory is 95 percent full, check what is in the 95 percent first.
For a rough Terminal view, vm_stat has a File-backed pages line. It is a close cousin of Cached Files, though not guaranteed to match Activity Monitor exactly. Multiply by the page size shown on the first line.
Why clearing the cache backfires
The purge command empties the disk cache. Apple's manual page describes it as a way to approximate a cold start for performance analysis, so it is a testing tool. Run it and the Cached Files figure drops, but the next time you open anything it is read from the disk again. Apps feel slower until the cache refills. Many RAM cleaners are a friendly wrapper around that.
How to tell real trouble
These are the signs worth acting on:
- The Memory Pressure graph is yellow or red for long stretches, not only during a spike.
- Swap Used climbs steadily while you work. A small number that stays put does not count.
- Apps stall when you switch to them, or the beach ball is frequent.
Apple's wording for the graph is that yellow means the Mac might eventually need more RAM and red means it needs more RAM. Swap Used can stay above zero for a while after demand drops, so look at whether it is growing.
| What you see | What it usually means |
|---|---|
| Free memory near zero, graph green | Normal. The cache is using spare RAM. |
| Large Cached Files figure | Normal. It is given back when needed. |
| Small swap that does not grow | Normal. Often left over from an earlier busy period. |
| Graph yellow for hours | Worth acting on. |
| Graph red | Act now. Quit heavy apps. |
| Swap growing steadily | Worth acting on, especially with a yellow or red graph. |
When one of the last three rows applies, the guide to freeing RAM lists what actually helps. To learn what the colors mean, read what memory pressure is. Apple's own description of each Memory tab figure is on its Activity Monitor memory page.
Boost shows cached memory as available, because macOS gives it back on demand, and it tells you when there is nothing to do. It is free and open source (GPL-3.0), and not notarized by Apple, so the first launch needs an extra step, described on its home page.
Install Boost
Free and open source, installed with Homebrew.