These devices all seem attractive, and each offers unique advantages. They're especially well suited for streaming media that you don't store on the iPad. However, they can't serve as backup or archival alternatives. They fail as backups because you can't clone an iPad to them, or even easily copy all of your non-iOS system data. Furthermore, in most cases, accessing data requires a special app designed to work with the device. This makes it impossible to open files from, or save files to, the device via other iPad apps.
Addressing all of these concerns would require that Apple substantially overhaul its iOS sandboxing and related restrictions. Apple has given no indication that it wants to do this. Until Apple removes these roadblocks--or third-parties find a better way around them--inadequate external storage remains a deal-breaker for going solo with an iPad.
Better support for wired peripherals
Storage may be the most critical example of the iPad's peripheral device deficiencies, but it is far from the only one. For wired connections, you are limited to connecting only one peripheral at a time--via the iPad's Lightning connector. And even with Apple's Camera Connection Kit, you are limited in terms of what you can connect. Most especially, a host of USB peripherals are impossible to use with an iPad.
Similarly, you can't switch to a larger screen by connecting a Cinema Display to an iPad, as you can do with a MacBook. You can't do this even via AirPlay. And even if you could, the Cinema Display is not a touchscreen, limiting how effectively you could use it.
Better typing capabilities
For me, the biggest reason I still take my MacBook with me when I need to get work done on the road is simply: typing. Whenever I expect to spend quality time with a keyboard, I want something beyond the iPad's virtual layout. Although Bluetooth iPad keyboards, such as the Zagg Folio or Logitech's Ultrathin Keyboard Cover go a long way toward addressing my concerns, they are not entirely satisfactory. For one thing, typing is a task that almost never benefits from a touchscreen. Every time I have to use the iPad's loupe tool, which I still do even with a physical keyboard, I mutter "fail." And, although the iPad has excellent text processing apps, they all fall short of the capabilities of the ones I use on the Mac.
One of the biggest limitations of the current version of iOS is that it cannot truly multitask. While some may prefer the simplicity and focus of "full-screen" mode (and Apple certainly promotes it), I don't. I would much prefer to be able to view my Twitter feed at the same time as I am writing an article. And I would like to be able to copy text from one document to another with both files viewable simultaneously. While all of this is easily accomplished on a Mac, it is currently impossible to do on an iPad.
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