Maybe the lower access time of WD2500JB can be explained by its higher spindle rotation speed? Western Digital has some experience in “overclocking” WDxxxxAB hard disks to 6,000rpm, so we had to check out this supposition, too. Utilities that measure the spindle rotation speed said that WD2500JB’s spindle rotated 7,200 times per minute. So, there is definitely no spindle “overclocking” here.

To find the answer, let’s take a look at the platter structure of our drives (to our regret, we don’t have any data for the model from  Maxtor, but it’s only a question of time…):

As you see, WD2500JB has much more servomarks per track (over 20%!) than WD2000JB.

Higher data density (the data density per track, to be more exact) gave the opportunity to put more servomarks, keeping the same effective track density. Thus, the linear speed didn’t drop down, but even grew a little. And the more servomarks per track there are, the faster the HDD will find a necessary track.

By the way, our study of the platter structures produces an interesting fact: the zero working cylinder of IBM Deskstar 180GXP IC35L180AVV207-1 is actually the 28000^th one counting from the platter edge! Yeah, every hard disk has the so-called zero track at a distance from the edge, but this distance is usually 700-800 cylinders…

It means that the effective capacity of the platter by IBM is much smaller than the “theoretically possible”! Let’s try to estimate the capacity of that theoretical platter. The cut-off block of 28 thousand cylinders is about one third of the 70000 cylinders (note also that the highest-density part of the platter is cut off). Thus, the hypothetical capacity of platters in IBM 180GXP equals about 83-84GB. What do you think, what platters Hitachi 250GXP will be based on? :)

Burst Rate results brought no surprises: WD2500JB was a little faster than WD2000JB, but far behind the leaders.