An Adaptive Partial Response Data Channel for Hard Disk Magnetic Recording

An adaptive data channel is proposed which is better able to deal with the variations in performance typically found in the recording components of a hard disk drive. Three such categories of variation were investigated in order to gain an understanding of their relative and absolute significance; variations over radius, along the track length, and between different head / media pairs. The variations were characterised in terms of their effects on the step-response pulse width and signal-to-noise ratio. It was found that in each of the categories investigated, significant variations could be found in both longitudinal and perpendicular recording systems which, with the exception of radial variations, were nondeterministic over different head / media pairs but were deterministic for any particular head / media pair characterised. Conventional data channel design assumes such variations are non-deterministic and is therefore designed to provide the minimum error rate performance for the worst case expected recording performance within the range of accepted manufacturing tolerance. The proposed adaptive channel works on the principle that once a particular set of recording components are assembled into the disk drive, such variations become deterministic if they are able to be characterised. Such ability is facilitated by the recent introduction of partial response signalling to hard disk magnetic recording which brings with it the discrete-time sampler and the ability of the microprocessor to analyse signals digitally much more easily than analogue domain alternatives. Simple methods of measuring the step-response pulse width and signal to noise ratio with the partial response channel's electronic components are presented. The expected error rate as a function of recording density and signal to noise ratio is derived experimentally for the PR4 and EPR4 classes of partial response. On the basis of this information and the recording performance it has measured, the adaptive channel is able to implement either PR4 or EPR4 signalling and at any data rate. The capacity advantage over the non-adaptive approach is investigated for the variables previously identified. It is concluded on the basis of this investigation that the proposed adaptive channel could provide significant manufacturing yield and capacity advantages over the non-adaptive approach for a modest increase in electronic complexity

A coding approach for detection of tampering in write-once optical disks

We present coding methods for protecting against tampering of write-once optical disks, which turns them into a secure digital medium for applications where critical information must be stored in a way that prevents or allows detection of an attempt at falsification. Our method involves adding a small amount of redundancy to a modulated sector of data. This extra redundancy is not used for normal operation, but can be used for determining, say, as a testimony in court, that a disk has not been tampered with

Ultra-high density recording technologies

The Engineering Research Center in Data Storage Systems at Carnegie Mellon University in cooperation with the National Storage Industry Consortium has selected goals of achieving 10 Gbit/sq in. recording density in magnetic and magneto-optic disk recording and 1 terabyte/cubic in. magnetic tape recording technologies. This talk describes the approaches being taken and the status of research leading to these goals

Metal evaporated tape: state of the art and prospects

Thin metallic films are the first choice for media in advanced rigid disk systems. For helical scan tape recorders thin metal films have become more important. The high signal-to-noise ratio per unit of track width allows very high densities. The preparation techniques and materials properties of the thin-film coating of metal evaporated (ME) are described. Important aspects are the size of the grains, the geometry of the columnar structure and the associated anisotropy. The consequences for the recording process are explained. Tribological and corrosion properties also help to determine the usefulness of a recording tape. Corrosion, wear, protection layers and lubricating organic films are briefly discussed

Approaching the event horizon: 1.3mm VLBI of SgrA*

Advances in VLBI instrumentation now allow wideband recording that significantly increases the sensitivity of short wavelength VLBI observations. Observations of the super-massive black hole candidate at the center of the Milky Way, SgrA*, with short wavelength VLBI reduces the scattering effects of the intervening interstellar medium, allowing observations with angular resolution comparable to the apparent size of the event horizon of the putative black hole. Observations in April 2007 at a wavelength of 1.3mm on a three station VLBI array have now confirmed structure in SgrA* on scales of just a few Schwarzschild radii. When modeled as a circular Gaussian, the fitted diameter of SgrA* is 37 micro arcsec (+16,-10; 3-sigma), which is smaller than the expected apparent size of the event horizon of the Galactic Center black hole. These observations demonstrate that mm/sub-mm VLBI is poised to open a new window onto the study of black hole physics via high angular resolution observations of the Galactic Center.Comment: 6 pages, 4 figures, Proceedings for "The Universe under the Microscope" (AHAR 2008), held in Bad Honnef (Germany) in April 2008, to be published in Journal of Physics: Conference Series by Institute of Physics Publishing, R. Schoedel, A. Eckart, S. Pfalzner, and E. Ros (eds.

Shift multiplexing with spherical reference waves

Shift multiplexing is a holographic storage method particularly suitable for the implementation of holographic disks. We characterize the performance of shift-multiplexed memories by using a spherical wave as the reference beam. We derive the shift selectivity, the cross talk, the exposure schedule, and the storage density of the method. We give experimental results to verify the theoretical predictions

Alignment sensitivity of holographic three-dimensional disks

We describe the rotational alignment sensitivity of three-dimensional holographic disks. It is shown that the reconstructed image always rotates by the angle by which the disk rotates; however, the center and the radius of rotation change as the recording geometry changes. A comparison among image plane, Fourier plane, and Fresnel holograms is given, and an optimum configuration (in terms of alignment sensitivity) in which the radius of rotation is zero is derived. We present experimental results and also discuss how the rotation alignment sensitivity affects the storage density and the readout–recording speed of the three-dimensional disk. A brief summary of other sources of misalignment is given

Magnetic disk

Magnetic disk recording was invented in 1953 and has undergone intensive development ever since. As a result of this 38 years of development, the cost per byte and the areal density have halved and doubled respectively every 2-2 1/2 years. Today, the cost per byte is lower than 10(exp -6) dollars per byte and area densities exceed 100 10(exp 6) bits per square inch. In this talk, the recent achievements in magnetic disk recording are first surveyed briefly. Then, the principal areas of current technical development are outlined. Finally, some comments are made about the future of magnetic disk recording