Like in case of WD2500JB (see our article called Western Digital WD2500JB HDD: More than Drivezilla?!), the answer to this puzzle lies with the number of servo-marks per track. The thing is that when the heads are moved to a new position, the HDD checks the trajectory on the layout with the help of the passing-by servo-marks. The more servo-marks are on a single track and the faster the rotation speed is, the earlier the electronics will find out if the desired track has been reached. WD2500 had 20% servo-marks than WD2000, while the number of cylinders grew up by less than 17%.

In Deskstar 180GXP IBM cared mostly about high linear speed, thus having increased the amount of servo-marks per track by only 10%, while the number of cylinders grew 27% bigger compared to 120GXP family. Of course, this couldn’t help telling on the average access time. So, it is not only the spindle rotation speed and average seek time that influence to time it takes the HDD to find the requested data. A little later today we are going to find out how all these things will tell on the HDDs performance in real tests.

And now let’s check the linear speeds of our testing participants during reading/writing of data blocks of various sizes:

The performance of 80GB and 180GB models appeared almost equal to that of 120GB/8MB model that is why we didn’t show them on the diagram. As you may see, single-platter modifications perform slower in case of small data blocks compared with the other models in the family. We double-checked the results many times with different HDD samples (we tested 4 of them all in all) and in different moments of time. We cannot find any other explanation besides the fact that the engineers slowed down the youngest models on purpose. 8MB buffer hardly affects the results here, although it does have certain influence: see the small “hump” around the 4KB data blocks area. Keeping in mind that in NTFS the cluster is mostly equal to 4KB, this is very good news.

During writes the situation becomes much more complicated. Single-platter models are still slower when processing small data blocks. 180GB model starts neck and neck with the 80GB one and both 120GB ones, however, as soon as the data block size exceeds 16KB, our hero immediately slows down to the level of a 40GB solution with slower platters. Here we can recall that this HDD performed the slowest of all during random writing… Strange, really… Unfortunately, we had only one chance to play with a 180GB model and didn’t have the opportunity to run the tests anew, to make sure.

Although… Not so long ago we tested Barracuda 7200.7 hard disk drives (see our article called Seagate Barracuda 7200.7 Hard Disk Drive Family) and discovered that the top models with ATA interface demonstrated absolutely the same linear speed drop. I cannot believe that LBA48 addressing can tell on the HDD performance like that!