Why is my internal memory almost full while the files add up to only a few gigabytes? My HTC One M8 internal memory is almost full (15.40 out of 16). The phone says it's mostly applications. But when I connect it to my computer, go to Internal Storage and add the sizes of all directories, the total is about 3 gigabytes.
Devices have different partitions for different purposes. Data storage is bigger because you will need to store your pictures etc. BUT the partition that your device uses for apps is always limited. You might want to move some apps to sd if you are able to.
For example here is the partition table to a Samsung Galaxy S5:

aboot -&gt; /dev/block/mmcblk0p6
apnhlos -&gt; /dev/block/mmcblk0p1
backup -&gt; /dev/block/mmcblk0p18
boot -&gt; /dev/block/mmcblk0p15
cache -&gt; /dev/block/mmcblk0p24
carrier -&gt; /dev/block/mmcblk0p25
dbi -&gt; /dev/block/mmcblk0p4
ddr -&gt; /dev/block/mmcblk0p5
efs -&gt; /dev/block/mmcblk0p12
fota -&gt; /dev/block/mmcblk0p17
fsc -&gt; /dev/block/mmcblk0p19
fsg -&gt; /dev/block/mmcblk0p9
modem -&gt; /dev/block/mmcblk0p2
modemst1 -&gt; /dev/block/mmcblk0p13
modemst2 -&gt; /dev/block/mmcblk0p14
pad -&gt; /dev/block/mmcblk0p10
param -&gt; /dev/block/mmcblk0p11
persdata -&gt; /dev/block/mmcblk0p22
persist -&gt; /dev/block/mmcblk0p21
recovery -&gt; /dev/block/mmcblk0p16
rpm -&gt; /dev/block/mmcblk0p7
sbl1 -&gt; /dev/block/mmcblk0p3
ssd -&gt; /dev/block/mmcblk0p20
system -&gt; /dev/block/mmcblk0p23
tz -&gt; /dev/block/mmcblk0p8
userdata -&gt; /dev/block/mmcblk0p26


Hope this helps.