Xox 360 Slim is not reading max storage

Im not certain, but there is a good chance this is how much is left after OS updates? Not sure if anyone else can chime in with this,

a quick search rendered me a few others seeing similar.

https://www.reddit.com/r/xboxone/comments/4z7kdg/xbox_one_s_500gb_arrived_365_gb_remain_after/

https://www.ign.com/wikis/xbox-one/Xbox_One_Actual_Hard_Drive_Space

Okay a little confusing but here's how it works. When any External Device be it a HDD or Flash Drive is used as a Storage Device (Memory for the Xbox 360), the Xbox 360 will only recognize it as such (a Storage Device) via the
USB. In short, a really huge External HDD becomes a 16Gb (Max) Storage Device from USB.

Some Games and some Features of Xbox LIVE require an Official MS Xbox 360 HDD that is for that particular Xbox 360 Console (ie Slim with Slim HDD). Simply using an External HDD will not work for these cases. Any External Storage Device is meant to supplement,
not replace an Official HDD or the performance of one that some Games and Features require.

As the post above this one said, your 4Gb Xbox is a "slim" Xbox. The "slim" hard drive is the one you want to use.

Read this for more info: http://support.xbox.com/xbox-360/accessories/storage

BJ @ I think the max size Xbox's able to read is 32GB external storage, last I read somewhere.

I think that the max amount of storage from USB is 16GB and you cannot set it up any other way. You will need to use the official Harddrives. If you have an xbox 360 slim, you can grab a 320GB of amazon for £60. If you have the original xbox 360 you could
buy a 120GB from amazon for £30 (used) and perhaps pick up another if you need storage. Thats the only way I can think of, sorry.