I'm a HP man, exclusively. That's all that I will buy. It include computers, printers, ink, DVD's and external hard drives, ex- modems, routers, network adapters. Oop's except flash drives too and I buy SanDisc.
I'm strictly an American patriot that believes in buy American. *( My last computer was shipped from Mexico. I have components from Ireland, China, Singapore, Thailand, Vietnam ----........ !!! ). When I meet my next computer made in America it will be my first. I won't be able to describe it but I'll know it when I see it. *( If I live long enough )>
The OFFICIAL HP recommendation is to power down before unplugging the HP hard drive. And power up after it is plugged back in. However, I like so many others, just unplug it and plug it back in powered up. I don't know what the detrimental effects are but I have been doing it for some time and I really haven't noticed any adverse effects. If your friend told you to power down before he/she was absolutely telling you the correct manufacturers information.
But I did notice that on my new HP computer with Windows 8 sometimes the hard drive isn't showing and sometimes it is. And if I plug in two hard drives called HP Pocket Media Drives, only one will show. But I think that's due to the USB 2's on the same system.
I read on HP's website that 1 TB cost $2,000 10 years ago. I was in Costco, a national membership wholesale chain here in the USA a couple days ago and they had a Seagate 4 TB Backup Plus External Hard Driver USB 3 or 2.0 plug and play connectivity *( That's plug and play connectivity BTW ! ), preloaded with automatic backup software. Works with PC's and Mac's. Item 695080.
Warehouse price $179. Instant savings *( at cash register ) $20. Your cost $159.99 !!!! Offer good Jan 31 - Feb 24, 2013.
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Bottom line. Both schools of thought are correct as it applies to specific manufacturers.