No such thing as disks with OS any more. Windows 8 has not had disks for years. Many computers don't even have drives for disks. The download is the official Microsoft version--the only one available. Go to Create Media site and make your own disk or thumb drive. No need to buy anything--that is a waste of money. Go here and select the version you have and follow the directions carefully-- windows.microsoft.com/.../create-reset-refresh-media
My device is Dell Inspiron 3542 with a default windows 8.1 home edition preinstalled.I had tried installing Ubuntu OS  and due to less attention from my part, the installation completely erased my windows partition. I had made a recovery disk on a portable hard drive but owing to carelessness, my cousin wiped out the entire hard drive thinking of it as unnecessary. I want to restore my PC back to the shipped OS but I do not have a recovery disk nor a manufacturer modified operating system.I tried looking into the support page but it says that recovery image is not available for the specified model of my product. Is there any way to recover back my old OS and can I request a installation disk from DELL.Please answer the following question.Thanks.  
Windows Installation Disk