Wikipedia:Reference desk/Archives/Computing/2017 March 26

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March 26

Remote computers communicating== internet

If tow computers after communicating remotely after they always using the internet or are there alternatives?31.4.140.133 (talk) 14:00, 26 March 2017 (UTC)

The internet is made of two things: physical computers that move data around, and protocols about how that data is handled. As far as the physical layer goes, you can always hang a copper wire between two distant computers and make them communicate by this channel, and it would not be on the internet. Or use radio waves (in either case, check applicable law before doing it).

Depending on how you count, a virtual private network could be "non-internet" for protocol purposes, but keep in mind the data is still transmitted over the general network. Tigraan^{Click here to contact me} 14:17, 26 March 2017 (UTC)

Computers transferred data in a variety of ways before the Internet existed. You can start with our articles on XMODEM, YMODEM, ZMODEM, uucp, Arpanet, and Network Control Program. CodeTalker (talk) 16:23, 26 March 2017 (UTC)

MS-DOS 6.x could communicate with a lapLink cable, using special crossover cables on parallel ports or null modem on serial port, but manual operating both computers was neccessary. HP 3000, HP 9000, IBM System i (AS/400) were made in a range from of PCs up to Mainframe computers. This machines could use one console. All other users used a computer terminal, with a serial connection to the central computer. A short distance is RS-232 / V.24, other serial links used differential signals on twisted pair cables for longer distances like ethernet or USB today. RS-232 was also a typical interface for dialup modems which allowed remote terminals. Radio modems also could be used. Therefore, the baudrate was reduced to fit the modem signals to frequencies of phonelines or even a bandwidth of radio. This caused that slow appering of letters on the screen in the 1970s and 1980s similar like constant fast typing a typewriter. BBS networks and other Pre–WWW online services were accessed over phone lines. Packet radio, which is modified X.25 was used on amateur radio, but strongly restricted even in some European countries. To transfer a program, computers with datasette could use a cassette tape adaptor. An analog datasette port (ear/mic/jack) to connect a cassette recorder can be connected to a radio or walkie-talkie. Often, this use was prohibited due it was called an "encrypted communication". But it also required manual operating the computers due the datasette had no extra hardware and used the whole ressources of the 8 bit home computer. Today some mobile apps for smartphones generate sounds to transfer any data to such old computers by using the earphone jack, using the app as a virtual datasette. --Hans Haase (有问题吗) 07:29, 27 March 2017 (UTC)

Charging Kindle with wall charger

Hi, I have a wall charger which states it's output is 5V DC 1A, but my Kindle says it requires input 5.25V DC max 500mA. Does this mean charging my Kindle with this charger is unsafe? I've done it several times but haven't checked the numbers till now. AvidReader98 (talk) 19:40, 26 March 2017 (UTC)

If it works then it is okey though you may be slightly undercharging the battery. Ruslik_Zero 19:45, 26 March 2017 (UTC)

5V is the standard USB voltage so it will be fine. It likely simply specifies 5.25V DC max as the maximum allowed voltage, which makes sense since +5% is the maximum allowed by the USB spec USB#Power. As for the current, there can be a risk that a device designed to supply 10A of 5V may not reliably supply 500mA or less at 5V so you do sometimes have to take care that there isn't a big difference between maximum current supply and what the device uses. But 1A and 500mA is too small to worry about unless there's a major design fault. And just as important, if the device is designed for USB power, it should be able to reliably supply 500mA or lower anyway even if it's designed for higher currents. Anyway the highest current generally supplied on a single USB port at 5V tends to be 3A. (5A is used at higher voltages. [1]) Some battery packs or chargers may have higher than 3A, but only if they want to be able to supply multiple ports at high current. P.S. I should clarify I'm only referring to situations where the maximum supply current is higher than the device current. In the reverse you perhaps should take a bit of care. Nominally if both device and power supply are USB and it's a standard USB cable, then it shouldn't draw more than 500mA unless the power supply is capable of it. But you still should take some care, especially if the USB power supply is of questionable quality. Of course if that's the case you should take care anyway. Nil Einne (talk) 11:07, 27 March 2017 (UTC)

I can tell you from experience that both the Kindle fire and the base Kindle (the second generation one with the e-ink display) will charge just fine from an inverter with those exact specs. It's a little slower than the provided charger, but I've noticed that there's actually a pcb with a chip in the provided charger, which is likely for optimization. ᛗᛁᛟᛚᚾᛁᚱPants Tell me all about it. 13:16, 27 March 2017 (UTC)

My experience with the Fire is that it won't show that it is charging in the interface (no lightning bolt on the battery indicator), but it does charge, eventually. 209.149.113.5 (talk) 13:30, 27 March 2017 (UTC)