What is the "External Hard Drive"?
The External Hard Drive, also referred to as the XHD, can be used as a strategic back-up plan in the case that someone either hacks you and deletes all of your software, (Or your needed software) or DDoSes you system and wipes your Software out.
For example; There's a DDoS coming my way, but there is an Exploit I wish to keep. I move my Exploit to the XHD before the attack reaches me, therefore keeping the Exploit safe.
The External Hard Drive is extremely useful as it cannot be accessed by anyone other than you. Which also means that it's safe from all attacks on your system, no matter how powerful. Use it wisely, however, as the XHD space can be both quite limited and expensive.
If you already have an XHD, you can choose to upgrade it or buy a new one.
How do I buy more XHD Space?
To buy more XHD space, you must first navigate to the "Hardware" section on the side-menu. From there, you can click on "External", which in turn brings up a tab displaying the prices of all XHD's and XHD upgrades available.