Under Serial-ATA Device Tree, System Profiler shows this for my April 2010 15" MacBook Pro/2.66GHz/Core i7/8Gb RAM/OS X 10.6.8 (Build 10K549):

Intel 5 Series Chipset:

Vendor: Intel
Product: 5 Series Chipset
Link Speed: 3 Gigabit
Negotiated Link Speed: 3 Gigabit
Description: AHCI Version 1.30 Supported

Is a 6Gb HDD compatible? (My external drive has failed, and I'm wondering whether I can replace my internal with a 6GB 7200 RPM drive [to use its 3GB 5400 RPM drive in my enclosure].)

Thanks.

You have not told us anything about the 6GB HDD, What its make and model are whether it is a SATA or ATA interface, etc. That is what will determine compatibility not the fact your Mac has an Intel Series 5 SATA chipset.

In general the size of the HDD should have no impact on compatibility. The drive incompatibility issues I have encountered were due to the bridge chip in the external enclosure and not to the drive mechanism itself. But reports can be confusing because they often refer to the enclosure/drive combo as if it were a single entity because that is how they were purchased. In truth the enclosure and drive may be from different manufacturers but the drive manufacturer may be hard to determine without disassembling the enclosure to physically examine the drive.

That doesn't necessarily follow. Some SATA-to_USB bridge chips, for example, are limited in the size of drive they can address. (There's firmware in the bridge chip that maps USB requests, which use block-based SCSI protocols, onto SATA requests, which use a frame-based protocol. The firmware may have a maximum number of blocks it can address, which results in a maximum hard drive size.)

Older external enclosures are limited to (approximately) 2.2 TB. The firmware in the chipset uses a 32-bit number to hold the block count.

Most modern external enclosures don't have this problem and can accommodate much larger hard drives, but there are still a few floating around that can't.

Thanks for the response, and sorry if I was unclear; I thought it would be obvious that I wasn't asking about a 6Gb HDD (Does such a beast even exist?), but about 3Gb/sec v 6Gb/sec Link Speed.

At any rate, though, I've decided against all the 6Gb/sec WD drives I was looking at in favor of this well-reviewed(*) Hitachi drive (despite the fact that it's manufactured by WD), because the Hitachis I've had have been trouble-free, as opposed to the OEM Toshiba that came with my MBP and the WD Scorpio blue I purchased, both of which tanked with bad blocks in the last two weeks. (*) More good reviews here.

Edit: Any opinions or stories about the drive before I buy it?

And getting back to 3Gb/sec v 6Gb/sec, does that work similarly to FireWire 400 v 800 and USB 2 v 3, with the 6Gb drive being compatible, but minimized by the 3Gb limit of the computer, or is the 6Gb/sec drive simply incompatible?

5GB drives are backward compatible with a 3GB connection but at the lower speed as you surmised.

Thanks for clarifying.

Some of the confusion in this thread could've been avoided if we all observed the standard convention that B stands for byte and b stands for bit.

Update...

1. After all that, the 3.0Gb/sec (as listed on both Amazon and Newegg) HGST drive I bought turned out to be a 6.0Gb/sec drive.

2. The Apple-branded drive that AppleCare gave me is actually an HGST drive.

3. For whatever it's worth, the drive I bought was made in China, while the AC drive and an old Hitachi I've got were made in Thailand. Hmmm...

Aside: joemikeb has said in the past that the best way to ensure that your data goes no further than you want it to go is to run your HDD's platters through a grinder.

Well, there may no longer be a need for such heroics. I opened up my dead WD Scorpio Blue drive and found that the platters were made of plastic that shattered into a million pieces upon being merely bent in half.

Nope!