[NTLUG:Discuss] OT: SCSI hard drive sizes...

[Stuart Johnston]

Robert Pearson wrote:
> On 10/23/06, steve <sjbaker1 at airmail.net> wrote:
>> Robert Pearson wrote:
>>
>>> All SCSI, both parallel and serial (SAS), spin 2x faster than SATA, have
>>> much more rugged construction, are dual-ported, have longer MTBF and
>>> longer warranties (5 yr vs. 1 yr for SATA).
>>> All of which cost money.
>> When the drive platter spins more rapidly, each magnetic 'bit' has
>> less time to induce a voltage in the drive head.  In order to get
>> enough signal from the head for the electronics to detect, the bits
>> have to be physically larger so they spend more time under the drive
>> head.  Larger bits mean less of them.
>>
>> (Actually, it's probably more due to the duration of the voltage than
>> the amount of voltage...but you get the idea).
>>
>> Hence there is a straight trade between speed and capacity.  You double
>> the speed - you halve the capacity.
>>
>> I presume that some marketting person decided that SCSI buyers are
>> more interested in performance than capacity - with the reverse
>> being true for PATA/SATA buyers.
> 
> What you say has been a factor in reducing capacity.
> I'm not sure how perpendicular recording, the new "hot" recording
> technology, works exactly. The capacity is increased by stacking the
> bits vertically, as I understand it.
> I didn't want to get down in the details too much.
> I'm pretty out of date on media read/write technology.

Watch this and you will understand (sometimes Flash is worth it):

http://www.hitachigst.com/hdd/research/recording_head/pr/PerpendicularAnimation.html