Jubimer- Received my Data Storage issue yesterday. Indeed, an editorial written by Uri Cohen of Velocidata on the apparent "hype" by drive manufacturers on stating MR-media areal densities. They use the maximum areal density in their claims, which occur near the center of the disk, rather than the average areal density, which is more realistic.
"Unlike drives with inductive heads, the areal density of MR drives varies greatly across the magnetic disk. Along the inner tracks of the disk, the linear (and areal) density is at a maximum, while along the outer tracks, it is a minimum."
Uri points out, as an example, a claimed density of 2.64 Gb/in squared nets an average density of only 1.47 Gb/ in squared, or a mere 56% of the claimed density.
"...the larger form-factor MR drives are severely penalized in both platter capacity and data transfer rates. While the most advanced (and expensive) 3.5 inch MR disk drives claim a top capacity of 2.2 GB per platter and data transfer rates of up to 180 Mb/s, advanced inductive torrodial heads may soon achieve capacities of up to 4.5 GB per platter and data transfer rates that exceed 300 Mb/s."
Back in the Feb. 1997 issue of Data Storage, they featured an article on torrodial heads, written by Uri Cohen, that stated it "will be particularly suitable for variable reluctance recording", which is just a fancy technical name for recording on "keepered media".
This was all important enough for the Editor-in-chief of Data Storage, Ernest Raia, refering to Uri's editorial, to state "...I can recall only one instance where a drive maker dutifully noted whether the areal density of its MR drive was a maximum or an average density. (IBM lists the maximum density - 2.64 Gbit/inch squared - of its latest Travelstar drive. The average density of the drive? IBM wasn't saying, though by Cohen's calculations, it's around half of the maximum density.)"
I compare this to stereo amplifier manufacturer's specifications for output power based on "peak" power output rather than the root mean square (RMS) at a specific total harmonic distortion level (THD), ususally well below .10%. In this case, they realize consumers are looking for the most power for the buck, and the uneducated are easily fooled into buying higher power and not comparing apples to apples. The high-end audio manufacturers are not usually guilty of this, but mostly I see it with mobile car audio (i.e. 35 watts/channel advertised is usually about half that power, at a respectable distortion level and using RMS power output).
|
