Is Serial ATA a Viable Alternative to Ultra ATA and FireWire?

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.