hesela.devTrack density
Track density is the number of recording tracks per unit distance measured across the tracks.
Tracks per inch (TPI) describes the cross-track dimension. For uniformly spaced track centers, TPI is the reciprocal of track pitch measured in inches. It is distinct from bits per inch along a track. [1]
Narrower pitch places more tracks in a given width. SMR uses overlapping writes to leave readable tracks narrower than the write head's footprint, so write-head width alone does not determine the final track pitch. [2]
Higher TPI at fixed BPI increases local areal density. At fixed disk radius and RPM it does not, by itself, increase the idealized bits passing a single head per revolution. Peak and average specifications must retain their original scope. [3] [4]
Reader width is not track spacing. Furrer et al.'s SrFe study combines a 29 nm reader with a calculated 56.2 nm track width, giving about 452 ktpi. Section V adds a positioning margin using 2 x sqrt(2) x 3 x sigma_PES + reader width, with sigma_PES rounded to 3.2 nm. Using 29 nm alone would imply about 1.94 times the track density. This is the authors' prototype design calculation, not a universal pitch rule. [5]
The recording test used an 8.7 micrometre writer, while servo tracking was evaluated separately. The 56.2 nm figure combines these results through a spacing model; it is not the written width of those experimental data tracks. [5]
Relations
- related
- Areal density, Linear recording density, Hard disk drive (HDD), Shingled magnetic recording (SMR)
Citations
- Furrer et al.: 201 Gb/in2 Recording Areal Density on Sputtered Magnetic Tape, IEEE Transactions on Magnetics (2018)
- Zoned Storage: Shingled Magnetic Recording Hard Disks, overview and interface implementations
- Hesela: Hard Disk Drive, density and transfer-rate interpretation
- Seagate: Enterprise Capacity 3.5 HDD v4 SAS Product Manual, 100726011 Rev. A, May 2014, sections 3.5 and 4.1
- Furrer et al.: 317 Gb/in2 Recording Areal Density on Strontium Ferrite Tape, author preprint v1, sections III, IV and V
Sources & caveats
- Furrer et al. (2018), IBM Research abstract, links 103 nm track width with 246.2 ktpi in a prototype tape experiment; no product-capacity extrapolation is made. [1]
- The author preprint was read beyond its abstract. Its 317.3 Gb/in2 result combines measured linear density with calculated cross-track spacing; section III.2 extrapolates the very low post-decoding error rate under an uncorrelated-byte-error assumption. [5]