On the HTC Desire X the memory (you would think you get 4Gb, but you don't) the partitions are as follows:
System is 940 MB,
Data is 1 GB, (This is what you get for your apps really)
'Phone' storage is 1 Gb
1 GB towards "internal SD".
Basically you only get 1Gb on the device for your apps.
You could use a micro SD card to expand your storage and move your pictures/music/media to it, and some apps still support App2SD functionality.
Keep in mind Chrome can run up to 300 Mb no problem, so a cache cleaner may well help you with storage. Lifehacker article on what to do if you run out of space.
You can't really mess with the other partitions without rooting and then partitioning your SD card with an EXT3/EXT4 partition and a ROM that supports Link2SD to 'trick' your phone into believing there is more internal memory. These partitions contain Android, HTC stuff, system apps, data partition etc. So you get 1GB in all (you have 138Mb left).
Otherabove is the OS, HTC apps and other Android related things, that you have no access to (without a rooted device).