As country music fans are hearing on the radio, size matters. In
a clever twist on the usual meaning, Joe Nichols sings about the
size of one's heart, "big ol' kisses that go on and on and never
end", and filling her world with laughter. Size matters.
In the world of computers, size matters, too, especially when it
comes to hard drives. How many gigabytes do you want or need?
But speed matters, too, and the quickest way to get a handle on
speed is by asking how fast the drive spins. After all, a 7200 rpm
drive has to move data faster than a 5400 rpm drive - or does
it?
It's Not That Simple
If you've been following
the story over on Macworld about different benchmark
performance between the 2.0 GHz white MacBook and the 2.0 GHz black
one, you might be scratching your head. Except for the hard drive,
the two 'Books were configured identically, yet some Speedmark
results were quite different.
The MacBooks, like most computers made today, can ship with
drives from any of a number of vendors, and Apple has made it easy
to swap the hard drive in the MacBook. By slipping a 7200 rpm drive
into the black MacBook, it came very close to matching the 5400 rpm
drive in the white MacBook.
What's up with that?
My first thought was that perhaps one of the drives had a bigger
cache than the other one. I've seen a big difference between 7200
rpm drives with 2 MB and 8 MB caches with my eMacs.
But as I read further, I saw that both drives had 8 MB
caches, yet the 5400 rpm Seagate was edging out the 7200 rpm
Fujitsu in several tests.
Digging Deeper
In the world of notebook computers, 4200 rpm drives used to be
the norm, and the first 5400 rpm drives provided a huge speed boost
(they spin 28.5% faster). Jumping to 7200 rpm spun drives 1/3
faster than that, but that's not the whole story.
Another way to make drives more responsive is to add a buffer.
In the ancient days of personal computing, drives simply read their
data and dumped it over a bus to the computer as fast as they read
it. Old timers may recall setting the interleave for drives used
with the Mac Plus, SE, and II - and wonder why we no longer do
that.
Setting interleave slowed down data transfer to a speed these
old computers could handle, and then someone came up with the
clever idea of building a data buffer (or cache) into the hard
drive. Now the drive could read the data at full speed, store it in
cache memory, and feed it to the computer at the top speed it could
receive data.
And that's why one of my favorite Mac SE speedups is putting in an hard
drive with a buffer to replace the ancient bufferless drives Apple
used back in 1987.
And the bigger the buffer, the more data in the cache, the more
efficient the process.
On top of this, there are different schemes for storing data in
the buffer. A drive may look ahead a few sectors, or it may buffer
the directory, or it may buffer writes, all of which can make
things more efficient.
Physics
That's drive electronics, and every brand has their own way of
doing things. So you can see why a Seagate, Hitachi, or Fujitsu
mechanism might offer different performance despite having
identical spin rates and buffer sizes.
But there's a third factor beyond RPM and cache size - data
density. Looking at the
manufacturer's specs for 5400 and 7200 rpm 2.5" Seagate
Momentus and Hitachi Travelstar drives, you'll see that the
transfer rate of the 7200 rpm drives is less than 1/3 faster than
the 5400 rpm drives - just 9% faster for the Seagate, and a more
impressive 28% faster for the Hitachi.
The big breakthrough over the past year or so is perpendicular
recording, which can easily store 50% more data per track. Just how
much data is there per track? That's hard to know, in part because
the manufacturers don't promote the number and also because the
amount of data stored per track varies between the inner and outer
tracks of a drive platter.
Still, if Drive A spins at 5400 rpm and stores 40% more data per
track then 7200 rpm Drive B, it will be able to read more date per
second. That might help explain how a 5400 rpm drive can sometimes
outperform a 7200 rpm one.
Conclusions
Tech Report has an
extensive article comparing these four drives. It looks at peak
transfer rate, how well each drive handles multiple data streams,
and typical read and write speeds. And just as Macworld discovered
with the MacBook and both brands of drives, Tech Report says, "At
times, those performance differences were surprising, as we
certainly didn't expect to see Seagate's Momentus 5400.2 beating
Hitachi's Travelstar 7K100 in so many tests."
Various drive parameters can be tweaked, optimizing a drive for
use by a single user or in a server, even optimizing for the way an
operating system works and how many data streams it may work with
at any given time.
In the end, there's more to picking a hard drive than capacity,
rotation speed, and buffer size. Seagate, Toshiba, Hitachi, and
Fujitsu each have their own buffering algorithms and optimization
schemes, so you'll want to look for benchmark results using the
hardware and operating system you'll be using. (OS X on Intel
Macs may produce very different results than OS X on a G4 or
G5 system.)
Price is the final factor (after all, Low End Mac is primarily
about value). If ultimate performance isn't crucial and the 5400
rpm drive is a lot less costly, it may well be a better choice for
you. But in the end you have to come up with your own value
equation - how important is capacity vs. performance vs. price?
Dan Knight has been using Macs since 1986,
sold Macs for several years, supported them for many more years, and
has been publishing Low End Mac since April 1997. If you find Dan's articles helpful, please consider making a donation to his tip jar.
