-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 El 2017-11-21 a las 13:04 -0800, Lew Wolfgang escribió:
On 11/21/2017 12:53 PM, Carlos E. R. wrote:
El 2017-11-21 a las 12:42 -0800, Lew Wolfgang escribió:
On 11/21/2017 12:21 PM, Wol's lists wrote:
Yes, we're routinely using Seagate 10-TB disks now. They're interesting, the top of the disk is welded into place to try to keep the helium inside. There's a low-helium alarm too. They're warrantied for 5-years, so we'll see.
I guess then that the gas is presurized. There might be some type of reservoir canister as well.
Why helium, and not nitrogen?
Helium is a noble gas, reacts with nothing. But nitrogen reacts with few things at those temperatures and is cheaper.
I "think" it has to do with the size of the atoms/molecules? Nitrogen has huge atoms compared to helium's and they'd interfere with how low the read/write heads can fly above the surface of the spinning media. Head altitude and data density are inversely proportional. Helium, being such a small atom, is hard to confine, which explains welding the case closed. Of course, I may be all wet here...
A nitrogen molecule is still ridiculously small compared to the head gap. I think the number of gas molecule layers in that gap can be calculated, but it would not be trivial for me after so many years from high school. I'm not sure the size of the molecule matters in gases for the number per volume. Re Avogadro number, mol size... Helium is indeed hard to confine, but not so hard as hydrogen, though. Any gas is difficult to confine for five years, I think. The length of the junction is very large in comparison to the volume. They would need a screw per centimeter. Perhaps glue would do with other gases and a reservoir canister. It might be marketing, LOL. - -- Cheers Carlos E. R. (from openSUSE 42.2 x86_64 "Malachite" (Minas Tirith)) -----BEGIN PGP SIGNATURE----- Version: GnuPG v2 iF4EAREIAAYFAloUl5kACgkQja8UbcUWM1zC3QEAjEBWnMjRIT5NG04dTygwupO6 19DnQIGF+en7QWWFbjIBAIk8ikhnXSNmSFUhdj0dIkXUndFt2ZTyHGVTsO8Pyjgh =0n/V -----END PGP SIGNATURE-----