By Hugh M. Sierra
This publication provides an exposition of the expertise, layout, association, and constitution of direct entry garage units (disk drives). It encompasses a dialogue of the evolution of the know-how (magnetic recording) and an evaluation of different garage applied sciences, together with optical recording. Examples of codes utilized in prior implementations of disk drives in addition to an software of disk force utilization dictated through reliability concerns also are integrated. The presentation assumes a minimal wisdom of magnetic recording, servomechanism layout, and coding.
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Extra info for An Introduction to Direct Access Storage Devices
T t3 Fig. 16. Approximation to the read pulse, (a) Graph of erf(/) vs. t. (b) Graph of exp(—t2) vs. /. pulse could be converted into a narrower pulse, as shown in Fig. 18. When this is done, Fig. 17. will be converted to Fig. 19. It is seen that in Fig. , due to the lack of neighboring pulse interference, the undesirable bit shift has been eliminated. As an added bonus, if this slimming down is done by a great amount (more than needed just to eliminate bit shift), the magnetic recording density could even be increased.
The effect of this bit shift is an out-of-step condition with the clock signal, which in turn may cause reading errors. It was stated before that the readback process can be considered linear. Therefore, if each individual readback pulse can be narrowed down (or slimmed) to the point where its effect upon neighboring pulses is negligible, then the bit shift λ could be eliminated. 4. 2 i J -1 1 0 T= Wj 2| -I Γε i. t t3 Fig. 16. Approximation to the read pulse, (a) Graph of erf(/) vs. t. (b) Graph of exp(—t2) vs.
17. Sequence of written transitions and corresponding readback pulses. Compos ite signal. Fig. 18. Wide read pulse and desired narrow pulse. Fig. 19. Sequence of readback signals with narrowed pulses. 4. Equalization «ffl Λ Pulse compressing network w, Fig. 20. Pulse compressing (or slimming) filter. " A long time ago, a method was used to increase the recording density on a magnetic surface, by means of two R - C sections between the terminals of the readback head (Gabor, 1959). The signal received from the magnetic head was thus slightly com pressed (slimmed down) before entering the read amplifier.
An Introduction to Direct Access Storage Devices by Hugh M. Sierra