Why the results of memory usage are not the same in Raspberry Pi?

Question

The following image is showing the memory usage of my raspberry pi. But why the results are not the same or similar? Does anyone help give some advice? Thanks.

Answer 1

The results look quite similar to me:

437MB = 437*1024 = 447,488KB
53MB = 53*1024 = 54,272KB

Those figures are not very different to the MemTotal and Active lines in meminfo. There's clearly some rounding going on, but otherwise they appear to match.

The disparity between the MemFree figures (384MB v. 302MB) are because "free" memory is a tricky concept. The OS considers that unused memory is a wasted opportunity, and caches just about everything it can. A newly booted system might have a lot of unused memory, but after it's been running for a while, and has accessed a lot of files, then there might well be almost none. Memory used to hold cached data is "used", but is still available for applications to use (the cached data can just be discarded), so you could call it "free". The task manager probably only counts memory used by actual applications. In this case the Cached 60,336KB accounts for most of the "missing" memory, 384-302 = 82MB.

If you have any swap memory in use then things get even more confusing.