MBP hard drive upgrade. 8mb or 16mb cache?

I am looking at these two drives:

http://www.amazon.co.uk/Western-Dig...1?ie=UTF8&s=electronics&qid=1218981289&sr=1-1

http://www.amazon.co.uk/Western-Dig...2?ie=UTF8&s=electronics&qid=1218981289&sr=1-2

They look the same except the second one has a 16mb cache. I have no idea what that means; can anyone with more savvy make a recommendation?

Thanks

 

The cache is just DRAM built into the drive that acts as a buffer. The physical disk itself can only read data so fast, like maybe 80MB/s, while reading from the cache can fully saturate a 300MB/s SATA II port. The cache basically keeps the most recent or most commonly used files and in the event that you use that data again, it'll send it directly from the cache rather than going to the hard disk. It's faster and saves power.

And those drives are not the same. The Scorpio Black spins at 7200rpm while the Blue spins at 5400rpm. That makes the Scorpio Black much faster, like 20%. Of course, it depends on what you do, whether you'll realize that speed. Copying files will obviously see the difference, while playing games won't, other than shorter loading times, but won't change your fps.

And with DRAM being dirt cheap now, I don't understand why hard drive manufacturers don't just include 256MB or 512MB of DRAM cache in hard drive. It'll really only cost them maybe $10, but it'll probably work as well as flash in hybrid drives.

 

Many thanks for the useful info. I hadn't spotted that the other one was 5400RPM. I want 7200

 

wow nice explanation itcommander.

what exact memmory cache type do HDD use anyway? if it is of a faster more expensive kind, then i understand why they use small capacity, perhaps to reduce power consumption or there is not enough space on the casing/board?

 

I'm pretty sure they just use SDRAM. Even 100MHz SDRAM can reach 800MB/s which is much faster than SATA II can handle. So it really doesn't matter what type of RAM they use. And they usually just put 1 chip on the board so they'll need to use higher density chips, which is more expensive. But 2GB SODIMMs can reach 2GB using 8 chips, so a single chip holding 256MB is certainly possible for commodity parts.

Maybe 256MB or 512MB cache is a bit much, but they can certainly do better than the 32MB of cache we see in desktop hard drives or 16MB we see in notebook hard drives. Supposedly, the new 2.5" VelociRaptors stuck with 16MB instead of 32MB because they could have accomplished the same difference improving their processing algorithms. So there may be dimished returns at 32MB. But, I don't see why they couldn't have improved their algorithms and included a 32MB cache at the same time or better yet, improve their algorithms to take advantage of a larger cache.

 

I'd suppose that the reason they didn't stuck a 256MB or 512MB cache on them is:

1. Size?
Do remember that usually there's only one DRAM chip soldered onto the controller board on the HDD. Since the normal SDRAMs used on notebooks/desktops are actually made from multiple chips (128MBx16 on a double-sided 2GB SODIMM), I don't see them fitting large amount of cache on it since the 'most users wouldn't notice any difference' factor comes into play.

2. Loss of data in case of power loss?
Imagine losing 256MB or 512MB chunks of data in an event of power loss due to the inability of DRAM to retain data over loss of current. It would've resulted in huge problems with data corruption I'd suppose?

 

My guess is the return in performance takes a nose dive with anything greater than 32MB. Or the algorithm that determines what gets cached or not is as good as they can get it, with respect to time and budget and bandwidth restrains on ATA and SATA connections.

In regards to data loss. I don't think the data in the cache is critical. In other words, the cache just holds a copy of data already on the drive. If the same data is requested twice, the algorithm checks to see if the data is in the cache first. If not, it reads it from the platter and then an algorithm determines if a copy should be placed in the cache for faster retrieval later.

The perfect drive would have no access latency, fast writes, faster reads, and gobs of bandwidth. Flash is where its at once newer methods are created to make these things even faster, cheaper, and denser. Even better would be material that is fast as todays RAM but non volatile.