The SATA 3Gbps vs. 1.5Gbps Issue

All unibody MacBook/MacBook Pros use NVIDIA’s GeForce 9400M chipset. The chipset includes native support for up to six SATA ports running at 3.0Gbps (300MB/s max transfer rate). Here’s a copy of OS X’s system profiler showing 3.0Gbps as the interface speed on the previous generation MacBook Pro:

3 Gigabit...only on the first unibody MacBook Pro

Unfortunately, the current version of the MacBook Pro appears to only support 1.5Gbps SATA. I’m not sure whether this is an OS, drive or hardware problem, but your drive is limited to transfer rates of 150MB/s. For most laptop drives, this isn’t a problem. Your 5400RPM SATA drive just isn’t going to be moving anything at 150MB/s. The real problem lies with high performance SSDs.

Let’s look at the read/write performance of the three top SSDs on the market today: the Intel X25-M, the OCZ Vertex and the Corsair P256:

New 15-inch MacBook Pro (73WHr battery) 4KB Random Read 4KB Random Write 2MB Sequential Read 2MB Sequential Write
Intel X25-M 54.2 MB/s 22.2 MB/s 230 MB/s 71 MB/s
OCZ Vertex (Indilinx) 34.9 MB/s 6.55 MB/s 256 MB/s 137 MB/s
Corsair P256 (Samsung) 29.1 MB/s 0.78 MB/s 207 MB/s 178 MB/s


You’ll see four categories of performance: random read, random write, sequential read and sequential write speed. All four categories matter to the performance of your hard drive but some are more noticeable than others depending on what you do.

Random read/write performance actually contributes to your system feeling fast more than anything else. These are the sorts of transactions that happen when you’re launching applications or searching for files. Sequential read/write transactions happen when you’re copying large files to/from your drive. The latter is less common than the former for most users but that’s why you don’t see the 1.5Gbps issue really impacting real world performance on the new MacBook Pro.

All three of the SSDs in the table above would be interface limited on the new MBP because of their high sequential read speeds. If you were copying large files from the SSD in your MacBook to a similarly fast device, the transfers could take longer. I doubt the performance difference would be significant or noticeable in real world notebook usage, but it doesn’t change that there’s no reason to take a step backwards like that. In the coming years we’ll see more drives that can consistently break 150MB/s; Apple artificially limiting performance today would just hinder progress.

I’m not sure what the issue is since the 9400M does support 3Gbps SATA. Perhaps it could be one of the mystery optimizations Apple did to increase battery life well beyond reasonable expectations? Or perhaps it’s just an issue with the firmware and something that will be corrected in the near future. It's worth noting that the version of OS X 10.5.7 that ships with the new MacBook Pro is a different build than the one everyone else gets to download.

It’s something to keep an eye on and I’ve already sent out some probes trying to gather more on the issue.

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  • fsardis - Tuesday, June 16, 2009 - link

    Except that SSDs do not use NCQ the way HDDs do therefore your entire argument is pointless. I think the performance specs given by manufacturers for their SSDs rely on NCQ to keep the SSD controller fed with enough instructions in order to achieve said performance.

    there only way to prove it is to test on SATA and SATA2 but from the little I have read on SSDs, the NCQ is actually important for them.
  • Samatros - Tuesday, June 16, 2009 - link

    Okay, I'm having a hard time understanding you. I think you meant to say that SATA-I doesn't have NCQ. You're wrong in that case, as the 925X SATA-I chipset does support NCQ, and does show a notable difference in benchmark. The NCQ support does not drop just because it's an SSD.

    Maybe you mean to say that "the NCQ is actually important for {SSDs}", which I completely agree with.

    I'm confused by your statement that "SSDs do not use NCQ the way HDDs do." What exactly do you mean? Are you referring to the mechanical aspect of most-efficient path of an HDD versus the command queue of an SSD? That somehow the gains made by always having a task queued is different between them, and having SATA-II fixes this?

    The biggest bottle-neck for these laptops isn't the SATA-I interface taking out precious literal seconds from their productivity, it's all the hours of whining.

  • rundll - Monday, June 15, 2009 - link

    For the moment the Sata 1,5 Gbps speed issue is not that crucial.
    In order to be able to take advantage of a faster read capability than 1.5 Gbps you have to be able to write the data to somewhere else with the same speed. Sure there is SSDs which sequential write speed exceeds 1,5 Gbps but not that many nor they do it that much faster than 1.5 Gbps. Not to mention that there isn't any HDD anywhere near this kind of write speeds.

    Having said that I still have to wonder why Apple is doing this. It seems so pointless to cause all the BS around this issue for nothing. Not to mention that in the (near) future this "problem" has to be taken care of as the SSD technology takes it's giant leaps. AND like said it is already today possible to find and put in SSDs to your notebook that will take a hit from a too slow Sata interface.
  • BushLin - Tuesday, June 16, 2009 - link

    "In order to be able to take advantage of a faster read capability than 1.5 Gbps you have to be able to write the data to somewhere else"

    For example, RAM. Read performance is what counts for loading times of just about everything. But in fairness, 1.5Gbps is pretty fast for a single drive even if it is capable of more.
  • Ailurophobe - Monday, June 15, 2009 - link

    The difference between Windows and OS X could IMHO be partially explained by their different schedulers. A quanta based scheduler like in Windows has to keep at least one core running. In OS X it would in theory be possible to sleep until next interrupt. I doubt this is the actual reason for most of the difference, but it is quite possible OS X really has an architectural edge when it comes to power efficiency.

    As for the SATA issue, it is a non-issue. While it is possible to install a drive that can read faster than that, it is infeasible to install anything to a laptop that actually uses data faster than that on a sustained and significantly frequent basis. There are some video and signal processing applications that can do it, but only a complete moron would run them on a laptop or indeed anything without significantly more RAM than any consumer level laptop can support.
  • mindless1 - Monday, June 15, 2009 - link

    It WAS only infeasible because laptop HDD performance was so lacking. What else can benefit? How about booting? Saving to hiberfile. Loading a game.

    It is untrue that there aren't constant gains, disk I/O is one of the biggest bottlenecks in typical laptop use. I'm not suggesting it wouldn't run great with the same SSD in SATA150 mode, but if you're paying a premium you should at least get something premium for the money.
  • evilspoons - Monday, June 15, 2009 - link

    Apparently someone (MacRumours, I believe) is reporting that Macs shipped with the built-to-order SSD option are seeing 3.0 Gbps on the SATA interface.

    This is all very shady, but it sounds like someone should be able to find the switch to flip (whether it's in firmware or what) to gain 3.0 Gbps mode for those of us upgrading the internal drive to an SSD.
  • BrooksT - Monday, June 15, 2009 - link

    As far as I can tell, it is literally impossible to get Vista to stop using the disk long enough for it to spin down. Turn off every non-critical service, kill Explorer and every application, and the core OS and required services will still touch the disk once or twice a second.

    If OSX can actually sit still for a moment and be happy with what it has in RAM, that may contribute to the different battery performance on the same hardware.
  • JimmiG - Monday, June 15, 2009 - link

    Yes, but what about XP? You can easily make the hard drive spin down under XP, yet older reviews comparing Macs under XP and OSX show similar results.

    When idle, a Macbook with a full Core2 CPU running OSX uses about as much power as an Atom netbook running XP. No PC laptop running any version of Windows comes close. Got to give credit where credit is due, Apple has really done a great job optimizing the whole platform (OS and hardware) for fantastic battery life. Either that, or Microsoft and its partners have done a horrible job.
  • Pirks - Tuesday, June 16, 2009 - link


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