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Comment: Re:Why not just do a software simulation? (Score 1) 56

by stepho-wrs (#47675987) Attached to: A Thousand Kilobots Self-Assemble Into Complex Shapes

From past experience, simulators are great for replicating known scenarios (including a limited set of failure scenarios).
But real, physical things will fail in strange ways that are hard to predict or can be hard to simulate.
Eg, perhaps some of them have a slight tendency to lean to the left (uneven legs during manufacturing), some of them might be intermittently blind on the right side but only when turning right (maybe manufacturing machine leaves a dry joint when soldering the right sensor, not found during stationary testing), parts start to fail intermittently as they age, the vibration of 10 neighbours is enough to cause trouble to one robot equi-distance from them all, etc.

Comment: Re:9 bits byte (Score 1) 113

by stepho-wrs (#47269665) Attached to: Unisys Phasing Out Decades-Old Mainframe Processor For x86
A lot of the 1960's big iron had 9 bit bytes - eg the venerable DEC-10. They need 36 bits to represent the range of data they wanted (typically floating point). Those 36 bits could only be divided according to 36 = 2x2x3x3 (ie chunks of 1, 2, 3, 4, 6, 9, 12, 18). Some used 6 bits to represent a character in a very limited character set, some used 9 bits to a character (not all bit values necessarily corresponded to a printable character). The big change to 8 bit bytes came from the IBM 360 when it choose 32 bits (32 = 2x2x2x2x2) and it's easy division into 1,2,4,8,16 chunks. The 9 bit byte was the standard and the 8 bit byte was the incompatible new kid on the block. Which is why the ITU says the unambiguous 'octet' instead of the ambiguous 'byte'.

Comment: Re:units (Score 2) 239

Likewise, I find Fahrenheit confusing every time I visit the US. 15-30C is comfortable (I live near a desert), 45C is try not to move weather (2 weeks in January) and 5C is wear a jacket weather. I can remember 100F only because I know it is body temperature (approx 37/38C). When visiting the US I usually make a little lookup table on a scrap of paper to convert between C and F.

Comment: encrypted (Score 1) 150

by stepho-wrs (#46580849) Attached to: Remote ATM Attack Uses SMS To Dispense Cash
ATM's make heavy use of encryption. Sensitive data (eg customer PIN) is encrypted so that you can not decode it. Unencrypted data is not sensitive (eg the dollar amount of the transaction). Each packet sent to the bank host is digitally signed. Each packet received from the host is also checked for its digital signature. The digital signatures have the time as part of the generation algorithm, so replay attacks don't work. If you monitored traffic on that cable then you would get a log of who took out money, the account number, the amount, the time and possibly how much was left in their account. You would get similar information by ransacking the receipt bin. If you tried to inject or replay packets in either direction then they would be rejected. I used to design EFTPOS credit card terminals. We designed them with the understanding that malicious people would be listening to everything on the cable and they would be trying to inject malicious data at every opportunity. Note that the cable might be ethernet, phone (ie modem), X.25, serial or a handful of less common types but the above applies to all of them. The worst you could really do is to cut that cable and deny the service to the customers.

Comment: Re:Um, nice, but not so fast (Score 1) 734

Home solar works better with a utility using hydro.
The utility allows the water in the high dam to fall down into the low dam, generating electricity using turbines.
Ideally your solar could be used to pump some of that water from the low dam back to the high dam.
At night time, the water can flow down again.
The two dams become a huge battery.

I believe many utilities already do this in reverse.
Average day time power is provided by gas/oil/coal/etc to cover slightly less than peak.
At night time, when user demand is lower, the excess power is used to pump the water up to the high dam.
Back in daytime again, the peak demand is provided by allowing the water to go down again through turbines.
Thus the gas/oil/coal/etc generators can be smaller as the production of electricity is spread across the entire 24 hours instead of at peak time.

Don't hit the keys so hard, it hurts.