Mac Musings

IDE Is Dead; Long Live SATA!

Daniel Knight - 2009.11.04 -

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IDE has been around since 1986, and Apple has been using IDE drives in Macs since 1995. Apple first used SATA drives in 2003, and as of 2006 they are in use across the Macintosh line (more on that below).

I'm a low-end Mac user by necessity, and all of the Macs I use regularly have IDE drives. I started to get an inkling that something was up a few months ago when I tried to find a hard drive deal for my 266 MHz WallStreet PowerBook - and DealMac didn't list any IDE notebook drives. This morning I checked DealMac for 3.5" hard drives, and received the message, "No recent deals found for IDE Hard Drives."

It's not that IDE hard drives aren't still available - they are, but the market has shifted to SATA, so there's little point running deals on IDE drives when people are looking for SATA drives.

On top of that, many new hard drives aren't available for IDE, just for SATA.

SATA for Older Macs

That got me to wondering if it might not make more sense to put a SATA controller card in one of my G4 Power Macs so I could benefit from the newest, fastest, highest capacity, and best deal hard drives.

No luck at DealMac, which only lists an eSATA adapter in its listing of SATA Controller Card Deals. Without SATA, that adapter does no good. On to Other World Computing, a company that knows and loves older Macs. Its listing of SATA cards for PCI Macs starts at $64 for a FirmTek card that works in any Mac with PCI slots and even supports Mac OS 8.x.

When you're looking at computers that sell for $200 to $300 on the used market, it's not easy to justify that expense. On the other side, you can buy a dual 1.8 GHz Power Mac G5 for $400 and have SATA built right in - along with more processing power (my fastest is a dual 1.6 GHz G4), a faster memory bus, support for 4 GB of RAM, and better graphics (my best video card is a Radeon 9000; a G5 Power Mac would give me GeForce 5200).

Makes you think twice about upgrading the old G4 Power Mac - not that I can afford either at present. Still, it's nice to know the options for future reference.

Another Option

Of course, a third alternative is an Intel-based Mac mini. For under $600, I could have a brand new 2.26 GHz dual-core Mac mini with 2 GB of RAM, a 160 GB hard drive, GeForce 9400M graphics, and Mac OS X 10.6 "Snow Leopard". I'm already using OS X 10.5 "Leopard" on one of my Power Macs, and it would be trivial to swap in a Mac mini. I can't even imagine the processing power compared with dual 1.6 GHz G4 CPUs.

On the used side, I could buy a 1.83 GHz Core Duo Mac mini for about the same price as that dual 1.8 GHz Power Mac G5 (less when you factor in shipping). Add $25 for Snow Leopard, and I'd be quite a bit less "low end" than I am today, even with the Intel GMA 950 graphics on the older Intel-based minis.

Despite the fact that any of these options are outside of my budget at present, it's good to have a benchmark when planning ahead. I suspect that I won't be doing much in the way of upgrading my wonderful old Power Macs and will eventually be buying an Intel-based Mac mini as my main Leopard machine. Although I like expansion slots and drive bays, realistically the Mac mini provides what I need.

SCSI vs. IDE

Apple was the first personal computer maker to adopt SCSI hard drives (starting in 1986 with the Mac Plus) and the last to adopt IDE hard drives (in 1995 with the Quadra 630 and PowerBook 150).

SCSI was and remains a superior protocol. With IDE/ATA drives, the computer's CPU is involved in a lot more drive management duties. With SCSI, most of those housekeeping details are handled by the SCSI chips, which are independent controllers. You can copy files from one SCSI device to another with no need to communicate with the CPU.

However, IDE has one huge advantage over SCSI: It's cheaper. Because it doesn't requires a SCSI controller, the controller board on the drive itself costs less to make, so in cases where the same exact mechanism is available for both protocols, the IDE drive will be cheaper - usually a lot cheaper.

Back in 1986, when the first SCSI Mac and the first IDE PCs came to market, 80386 CPUs were the top end of the market. 16 MHz 386 CPUs that had to manage the hard drive, knowing what files were stored on it and which tracks and sectors they occupied - details handled by SCSI. This took its toll on overall system performance, but at CPUs got faster and more powerful, CPUs needed to dedicate a smaller and smaller percentage of their power to the drive bus.

When Apple began the transition to IDE in 1995, it was used on its low-end consumer models, both of which ran at 33 MHz. IDE didn't come to the Power Mac line until late 1997, when the Beige G3 became the first "pro" Mac to ship with an IDE hard drive - and even then SCSI remained an option.

IDE vs. SATA

The IDE/ATA protocol advanced over the years, and the latest version (ATA-7 or Ultra ATA/133) supports transfer rates up to 133 MB per second, over eight times the bandwidth of the 16 MB/s ATA-1 through ATA-3 standards.

Just as USB replaced older, slower serial and parallel protocols and FireWire was designed to displace SCSI, Serial ATA (SATA) was designed to move beyond parallel ATA. The original SATA specification has a bandwidth of 150 MB/s, SATA 300 (a.k.a. SATA 2) doubled that, and the third generation SATA specification, released in May 2009, doubles that to provide 600 MB/s of bandwidth.

The biggest difference between SATA and IDE/ATA is the data connection. Parallel ATA and SCSI drives use those wide, flat ribbon cables most of us are familiar with. SATA, like USB and FireWire, uses a lot less wires, and all three of these protocols use round cables that are much easier to route inside your computer.

In the case of SATA, there are seven conductors - two pairs of data lines and three grounds. The connector is much smaller than the ones used for IDE drives (notebook IDE drives use a different, smaller connector than 3.5" and larger IDE devices).

Unlike IDE, where a bus can support two drives (master and slave) on a single cable, SATA is designed to use one cable per device, although port expanders (or multipliers) have been developed to allow more than one SATA device to connect to a single SATA controller port.

SATA has been around since 2003, and Apple was among the first companies to embrace it. The first Power Mac G5, released in June 2003, was the first Mac to use SATA. When Apple made the transition from PowerPC CPUs to Intel CPUs in 2006, it moved the entire Macintosh line to SATA.

SATA vs. FireWire vs. USB 3.0

Protocol       MB/s  Mb/s
USB 1.1          1.5   12
FireWire 400    50    400
USB 2.0         60    480
FireWire 800   100    800
SATA 150       150   1200
SATA 300       300   2400
FireWire 3200  400   3200
SATA 600       600   4800
USB 3.0        600   4800

ATA protocol throughput is always rated in megabytes per second (MB/s), while other serial protocols - such as USB and FireWire - are rated on megabits per second (Mb/s). Here's a quick comparison of total bandwidth. Note that in USB, no device can use all available bandwidth.

In terms of bandwidth, among the protocols in widespread use today, SATA 300 wins hands down with three times the bandwidth of FireWire 800, which itself has about 2.5 times the bandwidth of USB 2.0 for a single drive (a USB device can only use about two-thirds of total bandwidth). In theory, SATA wins hands down, although few devices can saturate the FireWire 800 bus.

Another area of difference is bus power. SATA is strictly a data bus; it is not designed to provide power to an attached device. USB has a 5V power line that can provide up to 500 mA of current (2.5 Watts of power) to a device, while FireWire can provide up to 30V of power, although 9V to 12V is typical on laptops. In terms of power, FireWire can supply up to 60 Watts, although 10 to 20 is more common.

USB 3.0, which will become widely available in 2010, is designed to be more competitive, providing at least 4V and up to 900 mA of current as well as additional data lines - USB 3.0 can send data over one set of lines and receive over another, while earlier USB protocols cannot send and receive concurrently.

Looking Ahead

In the short term, SATA 300 will continue to dominate inside the computer, FireWire - despite the superiority of more intelligent devices - will become increasingly marginalized, and SuperSpeed USB 3.0 will quickly become the norm for external devices that can benefit from its greater bandwidth and/or power. iPhones and iPods will charge more quickly, 3.5" bus-powered external drives may be possible, and simultaneous send and receive will give it a real leg up over USB 2.0.

Longer term, I can see USB 3.0 replacing SATA inside your computer. With SATA, you have two cables, data and power. With USB 3.0, there will be sufficient bus power for most devices, eliminating another set of cables inside your computer.

Looking at Apple's track record, I wouldn't be at all surprised to see it among the first to offer USB 3.0 on its computers - and perhaps the first to use it internally instead of SATA when native USB 3.0 drive mechanisms become available.

And in a few years, we may report, "SATA is dead. Long live USB 3.0!"