Using a USB thumb drive for backups?
in [Mac Systems]
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From: Jolly Roger on 20 Dec 2009 23:34 In article <201220092320284096%nospam(a)nospam.invalid>, nospam <nospam(a)nospam.invalid> wrote: > In article <jollyroger-C71582.21082620122009(a)news.individual.net>, > Jolly Roger <jollyroger(a)pobox.com> wrote: > > > > > > > I also doubt that the 500ma output of USB ports on a laptop is > > > > > > always > > > > > > a > > > > > > continuous stream without fluctuation. > > > > > > > > > > it's required. read the usb spec. > > > > > > > > Under all circumstance at every moment of every hour of every day of > > > > the > > > > year, without fail? Can anyone realistically make such an assurance? I > > > > think not. > > > > > > straw man. nobody can guarantee that it will *never* deviate outside > > > the spec. > > > > And that has been my point all along. Thanks. > > you seem to think it happens with regularity. it doesn't. I never said that at all. It's a potential problem with any USB bus-powered enclosure though, IMO. -- Send responses to the relevant news group rather than email to me. E-mail sent to this address may be devoured by my very hungry SPAM filter. Due to Google's refusal to prevent spammers from posting messages through their servers, I often ignore posts from Google Groups. Use a real news client if you want me to see your posts. JR
From: Tim Murray on 21 Dec 2009 09:57 JF Mezei wrote: > Even SCSI-1 from the 1980s would start to need additional work to > find a system capable of processing it. Maybe I should get into the business. I can still use SCSI-1.
From: Tim Murray on 21 Dec 2009 13:57 E Z Peaces wrote: > Tim Murray wrote: >> isw wrote: >>> Tim Murray <no-spam(a)thankyou.com> wrote: >>>> I'm using spark in the sense of an electron jumping from one contact to >>>> another as it gets in range. All connections spark but one exception: >>>> When the distance between contacts closes up so quickly that an >>>> electron does not have time to jump. >>> Most of the engineers I've known (in over 40 years of being one or >>> managing them) would only call it a "connection" if the pieces of metal >>> were in actual, physical contact, with nothing separating them. >>> >> >> I agree. I was referring to the time just before the actual connection is >> made or just after it breaks. I kinda thought the "gets in range" should >> have made that clear. >> > I've been trying to imagine plugging in a USB device before en electron > has time to jump. Superman could do it. > Plugging in a USB device could produce a static discharge of tens of > thousands of volts. I'd be concerned that the device was designed not to > be damaged by static. I wouldn't worry about damage from the 5V supply. > > The big problem with contacts comes not from closing but from opening with > an inductive load. There, the available voltage can be theoretically > infinite. A car starter uses a solenoid so that a spring can break the > arc quickly. All I was trying to explain was that all connections -- okay, the "act" of making the connection--even if quick and low power, generate some tiny spark.
From: E Z Peaces on 21 Dec 2009 13:52 Tim Murray wrote: > isw wrote: >> Tim Murray <no-spam(a)thankyou.com> wrote: >>> I'm using spark in the sense of an electron jumping from one contact to >>> another as it gets in range. All connections spark but one exception: When >>> the distance between contacts closes up so quickly that an electron does >>> not have time to jump. >> Most of the engineers I've known (in over 40 years of being one or >> managing them) would only call it a "connection" if the pieces of metal >> were in actual, physical contact, with nothing separating them. >> > > I agree. I was referring to the time just before the actual connection is > made or just after it breaks. I kinda thought the "gets in range" should have > made that clear. > I've been trying to imagine plugging in a USB device before en electron has time to jump. Plugging in a USB device could produce a static discharge of tens of thousands of volts. I'd be concerned that the device was designed not to be damaged by static. I wouldn't worry about damage from the 5V supply. The big problem with contacts comes not from closing but from opening with an inductive load. There, the available voltage can be theoretically infinite. A car starter uses a solenoid so that a spring can break the arc quickly.
From: Paul Sture on 22 Dec 2009 08:15
In article <1jb0xkw.1pg4j9z1c4ajswN%nospam(a)see.signature>, nospam(a)see.signature (Richard Maine) wrote: > JF Mezei <jfmezei.spamnot(a)vaxination.ca> wrote: > > > nospam wrote: > > > > > i didn't say there weren't. however, some new drive mechanisms use less > > > power than older ones. > > > > A 600 meg disk in the mid 1980s required a 10amp 115VAC circuit for each > > drive, and used a 1/3HP motor to turn the disk. The 250MB disk drives I was using in the early 1980s had a mechanism to fire each one up in sequence so that during startup the main circuit breaker didn't flip. > And weighed about 175 pounds and cost about $30,000 - at least one model > I recall did. I think those were the right numbers. I distinctly recall > helping our hardware guy remove one from its rack. I wasn't very smart > about how I positioned my hold on it. Once we were holding the full > weight, it seemed like the thin metal rail that I was holding it by was > cutting through my fingers. I had this horrified vision of dropping and > breaking a $30k piece of government equipment. I managed to avoid that, > but I still recall the pain. I don't recall how much those 250MB disk drives weighed but they were washing machine sized rather than rackable. Two gorilla sized guys were needed to get them upstairs. They did this stuff for a living and still turned the air blue with their curses. -- Paul Sture |