Memory not showing up on computer?

So I have a 32gb sd card in my hp omni10 tablet running windows 8.1. The C drive says it is 28.3gb so clearly 4gb are being designated to the operarting system and files. and when I highlight and look at the properties of all items in the c drive it says 21 gb. So it isn't the formatting of the drive or operating system because there's 4gb for that. What happened to the 7gb because only 21 out of the 28.3 are being used.

Computer Technician2014-03-05T08:42:34Z

Favorite Answer

Manufactures count 1000 MB as 1 GB. When actually
there is 1024 MB in 1 GB. Like I have a 1 TB HDD and
it shows 931 GB capacity.

Terrence2014-03-05T18:42:22Z

Make sure memory is pushed in.