Yes to Upgrading PlayStation 4 Hard Drive, No to External Hard Drive
Sony released an epic 160 question PlayStation FAQ on the US PlayStation blog that could answer all and any question you may or may not have about their upcoming console.
Under the PS4 System Details, the FAQ explains about what will and will not be possible regarding extra storage for the PlayStation 4. Like the PS3, you will be able to change the hard drive for the console. It comes with a 500GB 5400 RPM SATA II hard drive. Users will be able to install a new one so long as it fits with those standards and is no thicker than 9.5mm. Basically any standard laptop hard rive will do just lik in with the PS3. It also has to be larger than 160 GB, which if it comes with a 500 GB I don’t think will be much of an issue.
But the FAQ goes on to ask about connecting an external hard drive and for that it’s a flat out “not supported on PS4.” Given that connecting an external hard drive was a necessary step in changing your console’s internal hard drive for the PS3 as a back up I wish it was more clear. The question is about connecting to expand storage, but doesn’t mention data back ups.