Can I upload a directory with files and subdirectories, and it keeps the directory structure in the cloud?
Yes. Any files or folders you place in the local Dropbox folder will be synced to your account online, as they exist on your local drive.
What is the minimum cost of 1 month with minimum space (to test it)? Free?
Free. A Dropbox Basic account is free and include 2GB of space to start, and you can earn additional space through referrals and other promotions.
What is the cost of 2TB of space per month, billed monthly?
Typically, $9.99, but that could vary depending on currency, country, etc. You can see the pricing for your region on the Dropbox website.
Is there a Windows application to upload and download directories?
The Dropbox application keeps your local Dropbox folder in-sync with your account online. Anything you do in the folder is synced in real-time. Add a file or folder and it's uploaded. Add a file or folder through the website and it's downloaded. Delete a file, and it's deleted everywhere. etc.
If upload or download is interrupted, can I restart it - continue where it left off?
If the Dropbox app is syncing, it will handle that automatically. If you're uploading through the website, you cannot resume an interrupted transfer.
About how fast are upload and download? I have a speedtest. PING 10 ms. DOWNLOAD 120 Mbps. UPLOAD 6 Mbps. Approximate time to upload and download 1GB?
No one can answer that for you as there are far too many variable. Computer speed, drive speed, speeds from your ISP, the route you take to get to the Dropbox servers, any network latency along that path, etc. Everything will influence your transfer speeds.
Also, when you look at the transfer speeds reported by the Dropbox application, remember the following ...
Unless you specified otherwise, your speed test is run to a local server. For a more accurate result pick one close to the Dropbox servers which are in San Francisco. Also remember that ISPs have been known to provide increased speeds when performing speed tests.
While most ISPs and speed test sites display their results in bits (kilo or mega), the speeds reported by Dropbox are in bytes. Be sure to do the conversion before comparing. For example, a 600KB/s transfer speed as reported by Dropbox is approximately 4.8Mb/s.
And finally, each file that you upload through the Dropbox application is hashed, compressed, then transferred, encrypted, and stored on the Dropbox servers. That entire process is included in the aggregate KB/s speed that's displayed in the Dropbox sync status. In other words, it's not just a transfer speed and can't be directly compared to the upload and download speeds provided by your ISP.