On Thu 11 August 2011 11:27:13 Grant did opine thusly: > >> I'm testing this USB 3.0 bus-powered hard drive: > >> > >> http://www.amazon.com/gp/product/B0041OSQ9S > >> > >> and I get: > >> > >> # hdparm -tT /dev/sdb > >> /dev/sdb: > >> Timing cached reads: 8006 MB in 2.00 seconds = 4004.33 > >> MB/sec > >> Timing buffered disk reads: 252 MB in 3.01 seconds = 83.63 > >> MB/sec > >> > >> # hdparm -tT /dev/sdb > >> /dev/sdb: > >> Timing cached reads: 8230 MB in 2.00 seconds = 4116.54 > >> MB/sec > >> Timing buffered disk reads: 252 MB in 3.02 seconds = 83.55 > >> MB/sec > >> > >> # hdparm -tT /dev/sdb > >> /dev/sdb: > >> Timing cached reads: 8446 MB in 2.00 seconds = 4224.36 > >> MB/sec > >> Timing buffered disk reads: 230 MB in 3.02 seconds = 76.28 > >> MB/sec > >> > >> Wikipedia says USB 3.0 has transmission speeds of up to 5 > >> Gbit/s. Doesn't MB/sec denote mega*bytes* per second? > >> > >> - Grant > > > > 4000MB/s = 4Gb/s > > OK, I thought "B" designated bytes and "b" designated bits. So when > you see something like MB/s or Mb/s there's no way to know if it's > referring to megabits or megabytes?
B and b mean whatever the fuck the manufacturer felt like having them mean on any given day[1]. There's no rhyme or reason with disk manufacturers, so you have to resort to independant testers who will tell you that disk have usable capacity of X units, where units is an exactly defined thing that we all understand. [1] There are standards, but not enforceable so manufacturers can often do anything they want. Japanese sound amplifiers are the same - I've seen portable Sony units advertised as 5,000W!!!!! That's two hot water geysers, a stove and a few kettles of power. All out of size D torch batteries. yeah right. -- alan dot mckinnon at gmail dot com
