It has all those extra ports because it is based on an off-the-shelf prototyping board.
For you iPhone users who drool over the large displays of such Android handsets as ZTE's 5.7-inch Grand Memo or Samsung's 5.5-inch Galaxy Note II, cast your eyes on what could have been: Early iPhone prototype The iPhone that could have kept RS-232 relevant for another decade (source: Ars Technica; click to enlarge) The …
Its used worldwide for a massive range of products in industry. It's simple, cheap and plenty fast enough for sending commands or telemetry. Plus it is just a level-shift away from TTL serial, so it can quickly be turned into 485/422 for longer range- or stuck over a fibre. It's also very easy to build into embedded systems where there isnt room for a full TCP/IP stack or the like.
Long live RS232!
You always need some way to get access regardless of how successfully you manage to stuff things up. RS232 is especially useful when you knacker the TCP/IP stack or somehow mis-type the configuration or not-so carefully mis-type it's IP address.
Been there, done that, probably have a few medals somewhere. It's actually quite hard to permanently brick modern embedded systems.
Ok, @ian 22, what's confusing about baud? On a single level line (e.g. RS232) 9600 baud is 9600bps which is 960 octets per second. On an analog line with four distinct carrier frequencies (e.g. four audio tones) you get 9600 baud is 38400 bits per second or 3840 octets per. Each "baud" might consist of a chord of four tones...
Possibly interesting: 1000Base-T (gigabit) Ethernet can carry 2Gb/s (1GB/s in each direction) and is implemented as four 250Megabaud lines so the overall connection is 1Gigabaud and 2Gb/s...
Or possibly not.
One morning Mr. Jobs walks through R&D and sees one of the minions with an "i <3 Alan Kay" T-shirt. He goes up to him and says "Have you ever met him?", and the techie says "Yes! I sat through a few of his lectures, he's a genius! Think of all his ideas!" So Steve says to him "You know, if they were all that good, he'd be richer. But nonetheless, he did think up a thing called Dynabook somewhen in the 70's that never came to anything. If you think he's so great, then build me one; You have 3 days and $2000. I see you on Friday.". As Mr. Jobs word is law the techie toddles off and turns up on Friday with this thing. Steve has a play with it and is somewhat intrigued. He calls the guy and tells him: "Now make it flatter, here's $200.000, I see you in 3 months."
The rest is known.
The original Star Trek has a lot to answer for with Scotties inflation of time and then infeasibly fast delivery. For years plagued by managers assuming we were all like Scottie. He'd also ask the most junior team members for estimates of project duration.
I think I know what you mean, but Mr. Jobs would have been just the type of manager who would expect you to do a few 24h days (and the night, too) if he requests something to happen. He would know that the outcome of a rushed development couldn't be perfect (see original article), but would show if the direction of the idea is right; or at least what he wanted it to be. The rest is then "improvement only".
Being an apple product, I imagine having both type of ports would be useful - simply plug both ends of a standard printer cable in at the same time and watch it disappear up its own arse.
Seriously though it's an interesting point whether a tablet is seen as a host or a device. Surtace has a USB A so it clearly thinks it's a computer you plug devices into; most other tablets have a mini or micro USB meaning they consider themselves devices that can be plugged into a host.
A good number of, but not all, tablets and phones can act as host- 'USB OTG'. You notice that micro USB has 5 pins yet USB A has 4? Shorting two of them together will instruct a compatible device to act as host and read memory cards, USB HDDs and keyboards etc.
Check online for '[your device] USB OTG' before buying a cable. Making one yourself is a good test of your soldering skill and patience, though.
Another has remarked about USB OTG (my phone support *8* USB drives simulatenously, so some kind of powered hub is probably in order -- although I can plug a thumbdrive into a cable for exFAT goodness).
The obvious reason for the "B" port is debugging and development and general "this is how the device works". That "A" port is most likely there to support removable memory: it is infinitely easier to work on a system where you can remove the boot device and stick it into a host to fix whatever it is that you just broke.
(And the serial port is so you can instruct the thing to boot off the USB port, natch!)
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