Hard drives have been getting bigger, faster, and more affordable as
the years go by. At one time, Apple's 5 MB Profile hard drive for the
Apple /// was state of the art. Not much later, it was the 10 MB hard
drive in the IBM PC XT.
Today we live in a world where a 40 GB drive is considered small,
something you'll only find in entry-level systems.
We've also reached the point where FireWire and USB 2.0 have become
bottlenecks.
That's the big news out of Bare Feats over the past month. Today's
7200 rpm hard drives are so good at moving data, that the original
FireWire specification and USB 2.0 can't move the data as fast as the
drive can handle it.
It wasn't too long ago that FireWire 800 (twice as fast as the
original FireWire) only seemed reasonable for RAID setups, where
multiple drives are streaming data to and from the computer. According
to the latest speed tests at Bare Feats, that's even true of 7200 rpm
notebook drives today.
Parallel ATA
Most hard drives sold today have a parallel interface, one that
moves bits of data down a bunch of different wires. For the most part,
those are flat ribbon cables about 2" wide with plastic connectors on
each end.
Today's hard drives are descended from the original IDE (Integrated
Drive Electronics) standard, but over the years that standard has been
extended to support faster hard drives and higher capacities. For
instance, we've seen Apple go from a 16.7 MBps (megabytes per second)
drive bus in the beige
G3 to 33 MBps in the blue & white G3 to 66 MBps
in the Sawtooth G4
and finally 100 MBps in the Mirror Drive Door G4.
The parallel ATA specification tops out at 133 MBps, although Apple
hasn't implemented that in any model to date.
FireWire
Apple invented FireWire, a fast serial bus, to simplify things and
speed them up. FireWire debuted on the Mac with the b&w G3 in 1999,
and it topped out at 400 Mbps (megabits per second). That's the equivalent of
50 MBps, which is 50% faster than the IDE bus in the b&w G3.
Not that it really mattered, since hard drives were only then
squeezing past the 16.7 MBps data rate of the previous parallel ATA
specification. Drives got faster, but the standard FireWire port seemed
plenty fast for anything except RAID arrays.
The other advantage of FireWire is that the same thin data cable -
no more ribbon cables - moves data and provides enough power to run the
drive. Apple envisioned FireWire becoming standard for internal drives,
not just external ones, and built an internal FireWire port into the
Sawtooth G4 motherboards.
As drives got faster, Apple released the FireWire 800 specification,
which is twice as fast as the original, now commonly known as FireWire
400. FireWire 800 uses a different connector and is only found on 15"
and 17" aluminum PowerBooks, G4 Power Macs that only boot into
OS X, G5 Power Macs, and Xserves.
Serial ATA
Apple was on to something with their high speed serial bus, but the
rest of the industry passed on FireWire - probably over royalty issues.
The new standard for internal hard drives is Serial ATA, which supports
150 Mbps. That's a bit more than Ultra133 and nearly twice as much as
FireWire 800.
Today you'll find Serial ATA drives inside the Power Mac G5 and the
iMac G5. You'll also find it on a lot of low-end Windows PCs, and I
suspect we'll see it in every Intel-based Mac.
As with FireWire, a single cable handles data and power.
USB 1.1 and 2.0
USB was originally envisioned as a replacement for the parallel
ports and serial ports that had populated the rear of personal
computers since the 1970s. At 12 Mbps, it was fast enough for printers,
scanners, and external 4x CD burners. With the original iMac (August 1998),
Apple made it their default for mice and keyboards as well.
USB 1.1 was well suited for those applications, but it soon became a
bottleneck for scanners, hard drives, and external optical drives. It
just wasn't fast enough, so USB 2.0 was invented. With 480 Mbps
bandwidth, it's 40x faster than USB 1.1.
Bandwidth Reality
Although USB 2.0 at 480 Mbps sounds faster than FireWire at 400
Mbps, in reality no device on a USB chain can use more than two-thirds
of the bandwidth. That means that USB 2.0 throughput tops out at 320
Mbps - 20% slower than FireWire 400.
Apple was late in adopting USB 2.0, rightly seeing it as a
competitor to FireWire. Eventually they saw that the entire industry
had adopted it, and they've been including it on Macs for the past year
or so.
Bare Feats tested USB 2.0 drives against FireWire in May 2004 and
found that sustained read and write speeds with USB 2.0 drives were
only about half that of the same drives on a FireWire 400 bus on
Apple's hardware. (The same report showed FireWire 800 up to 50% faster
than 400. It also mentions that USB 2.0 is faster on Windows PCs, where
it rivals FireWire 400 for throughput. TechTV did a thorough comparison
on Windows PCs and found that FireWire 400 outperformed USB 2.0 by
15-70% depending on the test.)
Where Do We Go from Here?
We have to factor in two different things - maximum data rate of the
bus and maximum data rate of the hard drive. Today's 7200 rpm drives
serve up data faster than than either USB 2.0 or FireWire 400 can
deliver it.
If you're looking for maximum throughput from a single drive,
Ultra100 parallel ATA, FireWire 800, and 150 Mbps Serial ATA are plenty
fast, and if you're using a 5400 rpm hard drive, you probably won't
find Ultra66 or FireWire 400 becoming bottlenecks. (TechTV's tests
found 5400 rpm drives were slower over USB 2.0 than FireWire 400, but
you'll probably still be happy with USB 2.0 speed.)
For maximum throughput from a RAID array, which is definitely not
low-end stuff, look at Serial ATA. Not only does it have nearly twice
the bandwidth of FireWire 800, but each drive has a dedicated
connection to the computer. Unless you add FireWire 800 cards, all of
your FireWire 800 drives have to move data over the same bus.
For all practical purposes, USB 2.0 and FireWire 400 are good
standards. They offer half to two-thirds the performance of FireWire
800 and Serial ATA with a single 7200 rpm hard drive, and FireWire 400
has been built into every Mac released since 1999.
For flexibility, we recommend picking a drive enclosure with both
FireWire 400 and USB 2.0. You may never need one of those connectors,
but you'll only pay a few dollars more for the flexibility. That's what
I've been doing over the past year.
For performance, if you're using a 7200 rpm drive and have or may
move to a Mac with FireWire 800, consider a drive enclosure that
supports FireWire 800 in addition to FireWire 400 and USB 2.0. However,
they tend to be more expensive, since fewer Macs have FireWire 800
ports and the industry seems to be moving toward Serial ATA for
external drives.
For moving massive amounts of data, FireWire 800 could conceivably
reduce your copy time by one-third - great if you're in a hurry, but
not cheap. Most low-end users will find FireWire 400 completely
satisfactory, but for those who want to squeeze the most out of their
computers, FireWire 800 is the way to go.
