On 12/2/2014 4:57 PM, Dale E Sterner wrote: > Serial devices are always slow; I don't know how they get around it. > SD cards are serial like SATA and they really are slow. The hard drive > clock must be super fast to get those speeds. They also have to transfer > handshakes serially. I wonder how its done. Some really great > engineering there. > "Serial" in SATA has nothing to do with the serial you seem to refer as in RS-232 serial connections. The higher transfer speed is accomplished by running on extreme high clock cycles for the data signals together with a both a better shielding of the transmitting conductors (2 pairs of them, each transmitting wire separated by one of the 3 ground wires) and limiting the maximum cable length. That's the reason why all SATA connections are direct connections between motherboard and host device, not those ultra long 40 conductors(80 wires) PATA cables. While the initial SATA standard allowed for cables of up to 40in (100cm), you might have noticed (or not) that most SATA cables in a standard PC theses days is no more than 20in/50cm in length... And SD cards are in no way "SATA" and the reason why they are (relatively) slow has less to do with the way how data is transferred to/from them but with the way how the Flash RAM that those cards consists of is being "programmed" when written to. That's also why you have a far greater read than write speed on SD cards...
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