Analysis: Did Apple downgrade the new MacBook Pro's SATA interface?

A slower interface could limit the throughput of external hardware and SSDs

Apple Inc.'s latest MacBook Pro laptops came with a number of upgrades to processor speeds, RAM and hard drives -- not to mention reduced price tags.

Apple also reduced something else: the serial-ATA (SATA) drive interface, which dropped from 3Gbit/sec on earlier MacBook Pros to 1.5Gbit/sec. on newer ones.

The downgrade was initially picked up by Mac aficionados on the Web site. Computerworld then confirmed the SATA change on a new 15-in. MacBook Pro as well as on the smaller, 13-in. model.

The issue has cropped up on Apple's forums and on

It was not clear whether the SATA interface on the latest 17-in MacBook Pro or the ultra-thin MacBook Air were also revamped. Computerworld was unable to get an explanation from Apple about the change.

The move to a slower SATA interface has tech experts baffled, leading them to question whether Apple had encountered technical issues associated with the faster interface.

"I'm puzzled by it, as I know a lot of other people are. The only reason why I could think they would do it is there was some serious technical glitch -- maybe the [processing] chip, maybe the optical drive," said Tom Coughlin, founder of data storage consultancy Coughlin Associates Inc.

Coughlin said some industry rumors indicate there were issues with data transfer rates associated with the MacBook Pro's optical drive, which has a 1.5Gbit/sec interface, "but usually the newer SATA interfaces are downward compatible with older interface products," he added. "So I don't even know why that would be a problem."

Jim McGregor, chief technology strategist at market research firm In-Stat in Scottsdale, Ariz., believes Apple may have been seeing data error problems at higher I/O rates with the 3Gbit/sec SATA interface. "It may be that those were higher error rates than they preferred," he said.

McGregor noted that the slower SATA interface will not likely affect most MacBook Pro users, as the data transfers from traditional hard drives don't saturate a 1.5Gbit/sec SATA interface, let alone a 3Gbit/sec interface. However, users with USB hubs connecting multiple external devices -- such as flash drives or a hard disk drive -- to a laptop or desktop computer might saturate the 1.5Gbit/sec SATA interface, hampering I/O.

The most obvious limitation of a slower SATA interface would be to SSDs, which are more than capable of fully using a SATA 1.5Gbit interface, with many of the drives boasting 230MB/sec sequential read rates, as well as write rates above 150MB/sec.

"It really depends on how much you hit them," McGregor said. "In many cases, the average consumer isn't going to be tapping into that full [1.5Gbit/sec] bandwidth, but memory-hungry applications like those for gaming, digital content creation and database applications will peg it and will limit the performance of an SSD."

Using a hard drive interface like SATA for SSDs is not optimal for for the disks, which have gained popularity for their fast read speeds, lower power use and and ability to withstand physical shocks that can harm traditional drives. SSDs cost more per gigabyte than hard drives, and are offered as pricey options on all of Apple's MacBook Pro laptops.

Given the speed with which SSDs can move data, most original equipment manufacturers are likely to eventually embed the NAND memory chips used by the drives onto the motherboards of computers in order to take full advantage of the I/O capabilities of non-volatile flash memory.

"Storage will begin to look more like a memory module than a hard drive," said Dean Klein, vice president of Micron Corp.'s SSD group.

Copyright © 2009 IDG Communications, Inc.

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