We've been looking at Macs and hard drives this month. Our first article explained that today's 7200 rpm hard
drives are so fast that FireWire 400 and USB 2.0 are limiting the
performance of external hard drives. We recommended FireWire 800 for
external drives (assuming your PowerBook or Power Mac includes it).
We looked at the problems incorporating "big" hard drives (over 128
GB) in pre-2002 Macs in our second article. Our
recommendation was that you consider Ultra ATA 66 or faster PCI cards
to address this problem. It also gives beige G3s, blue & white G3s,
and Yikes! Power Macs much greater throughput.
In another article, we looked at
the pros and cons of various G3 models, often pointing to hard drive
issues and slow IDE buses as reasons to choose one model over
another.
Serial ATA
There's a faster solution that's become affordable in recent months:
Serial ATA. Serial ATA (SATA) hard drives have price parity with Ultra
ATA drives, and SATA PCI cards have dropped below the US$100 mark.
Serial ATA has more in common with USB and FireWire than with
parallel ATA (PATA). As the name implies, Serial ATA is a serial
protocol. It sends a single stream of bytes and doesn't require those
wide ribbon cables we've seen inside computers for years.
In the PC world, SATA is rapidly replacing PATA - even on relatively
low-end hardware. On the Mac side, it's only used in the iMac G5 and
Power Mac G5 at present. We're guessing that every Intel-based Mac will
incorporate SATA.
Serial ATA is fast. The specification calls for 150 MBps bandwidth,
a bit faster than Ultra ATA 133 and 50% faster than FireWire 800 (100
MBps bandwidth). That's fast enough for today's hard drives, and the
new SATA2 specification doubles that to 300 MBps.
Serial ATA PCI cards come in a wide variety of configurations. Basic
ones might have two internal SATA ports, while high-end ones might
support up to 8 drives in a RAID array. There are reasons you might
want to consider a card with external support.
Best of all, SATA cards can work in ancient PCI Macs and clones, as
well as versions of the Mac OS as far back as 8.0.
Serial or Parallel ATA?
With prices for Mac SATA and Ultra ATA cards so close, and with hard
drives selling at virtually the same cost these days, why would you
choose one protocol over the other?
If you already have the drive, it's pretty much a no-brainer. Buy
the controller that's going to work with it.
If you're planning to move to a newer Mac with Ultra ATA support,
you can save money by sticking with PATA for now.
But if you don't already have the drive and have a reason (bus
speed, limited number of ports) to buy an add-in card, why would you
choose Serial ATA over Ultra ATA?
It's a matter of looking back or looking forward. If you want drives
that will easily plug into the existing bus on an older Mac when you
upgrade from your current one, parallel ATA makes sense. But if you
want the drives to work with a future Power Mac G5, SATA definitely has
the edge.
External SATA
For external drives, we've recommended FireWire 800 because Apple
builds that into their top-end pro models. FireWire 800 is a great
solution, because not only is it faster than almost any drive made
today, but with the right cable you can connect a FW800 drive to a
FireWire 400 port.
That said, FireWire is facing stiff competition from SATA for
external drives. eSATA (for external SATA) is twice as fast, and you
don't need Ultra ATA to FireWire 800 bridges - you can just use a SATA
drive.
Best of all, for top throughput, SATA provides a single data channel
between each hard drive and the SATA controller (although there is a
push for "port multiplication", which would allow two SATA drives on a
single bus). By contrast, all the devices on a FireWire bus have to
share the same bandwidth. That points to one FW advantage: You can
string devices together.
Another FireWire advantage: Bus power. Although most 3.5" FireWire
drive/enclosure combos can't run from bus power, almost every 2.5" one
will. For portability, that means you don't need to carry a power
brick, making FireWire a good option for people with portable computers
or who want to quickly and easily move a hard drive from one computer
to another.
With today's single hard drives, you're really not going to see a
difference between Ultra 133, SATA, and FireWire 800 performance. The
minute you go beyond one drive, the fact that SATA provides a dedicated
data path for each drive gives is a real advantage, and this is
especially true if you're putting together a RAID array.
This being Low End Mac, we don't expect many of you will be doing
that. We see FireWire as today's solution, but SATA is the solution for
tomorrow. FireWire had a decent run, but we're already seeing digital
camcorders move to USB 2.0. Nice as it is, FireWire is being undercut
at the bottom by USB 2.0 (and that includes Apple's decision to no
longer support FW in new iPods) and overshadowed by SATA at the
top.
Don't be surprised to see the Intel-based Mac include external SATA
ports as well as using SATA for their internal drives - and don't be
surprised to see Apple begin phasing out FireWire starting within the
next year or so.
It's just one more case of Apple moving away from their own
standards to those used by the industry at large. In the long run, we
all benefit, and in the short run you can begin the migration to SATA
if you need to add a drive and PCI card to your system anyhow.
