Memory pressure, not free RAM: the only number that counts
A full memory bar is healthy — and a whole industry sells software that calls it a problem. What pressure measures, why "free up RAM" makes a machine slower, and how a real shortage actually looks.
There is one number that gets misread on every computer, and a whole genre of software lives off it: free memory.
An empty stick of RAM is wasted money
macOS and Windows fill spare memory on purpose. Anything not needed right now becomes file cache: libraries an app loaded ten minutes ago, thumbnails, parts of the documents you are working on. That is not a leak, that is the design. Memory left empty has done nothing for you.
So "only 1.2 GB free" on its own says nothing at all — about as much as a full fridge.
What actually counts
The question is not how much is free but how hard the system has to work to keep everything in memory. That is what pressure measures: as its own figure on macOS, derived from commit charge and paging activity on Windows.
Normal
Everything runs from RAM. 95 % used is fine.
Elevated
Compressing, dropping cache, first swapping.
Critical
Paging to the SSD continuously. This is what feels slow.
A machine at 96 % used with green pressure is healthy. A machine at 60 % used with red pressure has a problem. Usage alone does not tell the story.
The four states behind the colour
| State | What the system is doing | Do you notice? |
|---|---|---|
| Free | unused memory, waiting for work | no |
| File cache | recently read files kept ready | yes — everything feels fast |
| Compressed | rarely used pages packed down | barely; costs some CPU |
| Swapped | pages living on the SSD | yes — this is the stutter |
The step from "compressed" to "swapped" is where a metric turns into an experience. Everything before it is bookkeeping.
Why software still offers to "free up memory"
Because the number is visible and the button feels good. What those tools usually do is purge or an equivalent call: they throw away the file cache. Afterwards the display says more is "free" — and the machine is slower for the next few minutes, because everything it just discarded has to come back from the SSD.
It is metric optimisation. The readout wins, the person loses.
The curve beats the moment
An instant value cannot tell "an export is running" from "something is wrong here". A curve can:
- Sawtooth — rises while you work, falls afterwards: normal.
- Staircase upwards — rises and never returns: something is not releasing.
- Permanently high with swap — not enough RAM for what you are doing. No tool fixes that; fewer things at once or more memory does.
That is why BalaneDisk draws the forecast as a straight line over the curve rather than as a model: you should be able to check it against the measurement instead of trusting a number whose origin you cannot see.
Short version
- 01Ignore "free memory".
- 02Read pressure — over hours, not in the moment something annoys you.
- 03If pressure stays elevated, go looking for the largest consumer, not for a release button.
- 04If none of that applies: your computer is using the memory exactly as you paid for it to.
- How much free memory is normal?
- Very little. macOS and Windows deliberately fill spare memory with file cache, because empty memory does nothing for you. Five percent free with green pressure is a healthy machine; forty percent free with red pressure would be a sick one.
- Does "free up RAM" or purge help?
- The readout looks better for a moment, and then the machine is slower for several minutes: everything thrown out of the cache has to come back from the SSD. It optimises a metric, not the experience.
- How do I know I actually need more RAM?
- From the curve, not the moment: pressure that stays elevated for hours and does not fall after you quit large applications, together with growing swap. If it only spikes during exports and settles afterwards, it was the export.