By Hugh M. Sierra

ISBN-10: 0126425809

ISBN-13: 9780126425802

This booklet offers an exposition of the know-how, 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 evaluate 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 by means of reliability issues also are incorporated. The presentation assumes a minimal wisdom of magnetic recording, servomechanism layout, and coding.

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In the frequency domain, it is possible to say that the narrower pulse out of the network contains largely increased high frequencies compared with the wider input pulse. This implies a certain "boost" of the high frequencies, leading some people to believe that this process of attenuat­ ing some frequencies and boosting others implied an "optimum" fre­ quency spectrum for the readback signal (thus the term "equalizer," although in reality, there is nothing to "equalize"). In reality, this is quite an optimistic exaggeration because quite different frequency spectra (not a unique one) are successful in narrowing the readback pulses.

Q Fig. 22. Components of the pulse slimming filter output signal. 46 MAGNETIC RECORDING FOR DIRECT ACCESS STORAGE DEVICES |F,0)| = V5"exp(-^) ^ο(τω)| = — e x p ( - - - 2 ) Fig. 23. Curves of the magnitude function, (a) For the input and output pulses, (b) For the desired network. 6572801 ± ;Ό. 22474487 + ;Ό) Φ \ (0± ιΌ. 70710678) Poles -koi/1) Zeros H(s)H(—s). ±(±1+/0) Φ Approximations to Table 2 . 2 . 48 MAGNETIC RECORDING FOR DIRECT ACCESS STORAGE DEVICES construct a rational approximation (ratio of polynomials) to H(s), thus making sure that the resulting filter is realizable.

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. Other implementations included active elements and a tapped delay line with three operational amplifiers.

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