On Wed, 10 Oct 2001 21:44:58 -0000, dplatt@radagast.org (Dave Platt) wrote:

>>will i notice a difference in quality between the two types of drives?
>
>Do you mean "quality of the drive itself" or "quality of the video you
>record on the drive"?
>
>> i've
>>only had experience with scsi drives, so if the quality is different between
>>these two, i'll splurge and get a 7200 i suppose. can anyone give me some
>>help?
>
>Well, the 7200 RPM drives spin faster. This means that you usually
>save a millisecond or so on each read or write, due to the reduction
>in rotational latency - you don't have to wait as long for the desired
>sector to spin around and come under the head.
>
>If you're comparing 5400 and 7200 RPM drives, you'd want to do so on
>the basis of "all else being equal". Unfortunately, all else is often
>*not* equal.
>
>By spinning the drive faster, the drive increases the rate at which
>the medium passes under the head. If the drive is to have the same
>areal density (the same number of bits per square inch) and thus the
>same number of sectors per track, this means that the data rate
>through the read/write heads and electronics must be increased. On
>today's high-density drives, this isn't always possible... even a 5400
>RPM drive can be pushing the high-frequency limits of the heads and
>electronics when the drive is reading the outer-diameter portion of
>each platter.
>
>This may mean that a 7200 RPM drive must have fewer sectors per track,
>to keep the data rate down. To compensate, it must either have more
>tracks per platter (and thus use a narrower track spacing and perhaps
>a narrower head), or more heads and platters (adds cost), or lower
>capacity. Or, the manufacturer may "push" the heads and electronics
>harder, at the expense of an increase in the low-level bit error rate
>(requires I/O retries) or the number of sectors whose media quality
>isn't quite high enough to be used reliably (requires "reassigning" or
>"slipping" the sector, thus reducing throughput every time you try to
>access the sector).
>
>I recently compared one manufacturer's 5400 and 7200 RPM 60-gigabyte
>IDE drives. In the case of the samples I was working with, the 7200
>drive showed substantially poorer predictability (there were many more
>reassigned blocks than on the 5400 RPM drive). If I recall correctly,
>it's sustained data transfer rate (on large sequential-block
>transfers) wasn't appreciably better than the 5400 RPM drive. It did
>seek faster, by a millisecond or so, but this isn't necessarily
>relevant in a streaming-video application.
>
>7200 (and faster) drives often run hotter than 5400 drives, which can
>lead to a reduced lifetime.
>
>Rather than trying to make the decision on a simplistic basis ("5400
>or 7200") you should look at your actual needs. If a 5400 RPM drive
>is fast enough to keep up with the data rate you need for your video
>(on your computer, with your operating system, with your software)
>then that's what I'd suggest going for. On the other hand, there are
>DV modes which require a higher bit-rate than a single 5400 RPM drive
>can provide - for these, your choices are probably to go to a
>7200-or-faster drive which is optimized for high transfer rates, or to
>implement some sort of RAID array using a pair of independent device
>controllers.