Install whatever you want? Try installing an .exe file on a Mac and see what happens. I guess OSX isn't a real OS. ...ALL programs are OS limited.
That point went over your head. The point is that it is an open ecosystem, if my friend codes an app, I can install it whether Apple allows it or not. I can have root access if I want it. I can install software to deal with any common file type on a Mac, unlike the iPad.
User access to the file system.
There's no user accessible file browser on the iPad. Mac has Finder.
Full input/output? There is no need for ports, if this is what you are referring to? Everything is done wirelessly in my case.
An iPad can't be a USB host to a 3TB hard drive, or connect to devices via Firewire, or connect to a wired LAN via gigabit ethernet. The only standard port is has is for headphones/speakers.
You talk about adding monitors. I laugh at that.
Why? Right now, I have an external 23" 1080p Dell display plus my MBP's internal, and soon I'm going to a triple Dell setup, with the widescreen in the middle, and two 17" wings. Try doing THAT with an iPad. You get an effective screen real estate of 1024x768.
Also, there is no storage expandability on the iPad. My MBP right now has 800GB of internal storage plus 6TB of external. I'm going to pare down to 5TB of external, but eventually I will upgrade to 1.25TB of internal. Try that on an iPad.
They tend to have those godawful, mushy dome keyswitches.
That's one issue. Mine is mushy, but I haven't found a natural version of anything like DAS Keyboard. If I did, and the contour was as good as the Microsoft one, I'd switch.
It's not necessarily a question of being able to fit a 23" monitor physically into your home. Sometimes it's a question of, "do I make room for an extra desk with a stationary computer, or do I make room for something else that's important to me?"
Computer is a pretty important part. Depending on where I end up living, I am probably going to do two triple-monitor setups, my personal machine (MBP), and my workshop machine (I'll get a cheap i5 tower with Win7). Screen real estate is a good thing.
"Full" is incredibly vague. iPad has I/O. It doesn't have the same I/O that PCs have. And every PC has different I/O options. Doesn't make them any less "full."
Gigabit Ethernet, Firewire, USB 2.0 host, SD slot, mic in/out. I.e. what my MBP has.
Can't upgrade laptop monitors either, sorry. And again, if you mean external monitors, you can use external monitors for iPads too; wired or wireless. Ever heard of AirPlay mirroring? Or the VGA adapter? Both are pretty fantastic when it comes to giving presentations.
Not extended desktop, and the second monitor doesn't have touch anyways, so it doesn't make much sense. Yes, I've used AirPlay mirroring. Gimmicky. I use my MBP for presentations, thank you very much. It actually can open .pptx files properly.
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The question was "What exactly does a real 'OS' do to make it a real OS?" .
1. user accessible file system
2. open installation of software
3. add on 3rd party hardware through standard ports
I do agree with your point about a 10 inch screen being pretty limiting, but then, I don't expect a motorcycle to be able to haul my luggage.
By the definition of running some sort of OS, and having CPU, hardware, some form of I/O, yes it is computer. Just like a Motorola DCX3400 is a computer, or a heavily-skinned feature-phone is a computer. The only material difference there is user-installed apps, although boxes like TiVo are moving that way to a certain extent.