Computer hard discs

Another recent discovery is that of collosal magnetoresistance (CMR), in which the electrical resistance of a material changes dramatically in the presence of a magnetic field. This property is important in the devices which read data on magnetic storage devices, such as computer hard discs. 

Magnetic hard discs are used in computers to store information in the form of magnetic bits on a ferromagnetic alloy film. To protect the magnetic medium, a hard carbon coating about... 

Is this an Uncorrelated Hard-Disc Fluid In order to answer this question we compute a 2D CLD and test, whether the function is positive everywhere. In this case the equatorial streak can be considered pure particle scattering. 

In general, it is most efficient for the microprocessor to access and store in the semiconductor main memory (DRAM) alone because the DRAM access time is < 100 ns. However, DRAM is volatile and any information in the DRAM is lost once the computer is turned off. Thus, lower level of information storage devices is essential. The latter may include magnetic hard disc, magnetic floppy drives, etc. As a rule, the higher-level storage media are... 

A variation of the TCSPC technique does not build up photon distributions but stores information about each individual photon. This is called time tag , time stamp , list , or FIFO mode. The memory is configured as a FIFO buffer. For each photon, this method stores the time in the signal period ( micro time ), the time from the start of the experiment ( macro time ), and the data word at the channel input. During the measurement, the FIFO is continuously read, and the photon data are transferred into the main memory or to the hard disc of a computer. Advanced TCSPC devices often can be configured either to build up a multidimensional photon distribution or to store the individual photons. The FIFO mode is described in Sect. 3.6, page 43. 

The time-tag mode in conjunction with multidetector capability and MFIz counting capability was introduced in 1996 with the SPC-431 and SPC-432 modules of Becker Flickl. Its large potential in single molecule spectroscopy began to attract attention when sufficiently fast computers with large memories and hard discs became available. 

The single-photon pulses of the detectors are fed into a router (see Sect. 3.1, page 29). Por each photon detected in any of the detectors, the router delivers a single-photon pulse and the number of the detector that detected the photon. The TCSPC module determines the time of the photon in the laser pulse sequence ( micro time ) and the time from the start of the experiment ( macro time ). The detector number, the micro time, and the macro time are written into a first-in-first-out (PlPO) buffer (see Sect. 3.6, page 43). The output of the PlPO is continuously read by the computer, and the photon data are written in the main memory of the computer or on the hard disc. 

Fig. 5.18. Write/read head for hard-disc computer systems. (Adapted from White, 1985.)...

Optical media is more durable than electromagnetic tape and is less vulnerable to environmental conditions. With the exception of Blu-ray Discs, the speed of data retrieval is considerably slower than that of a computer hard drive. The storage capacity of optical disks is significantly less than that of hard drives. Another, less common form of optical storage is optical tape, which consists of a long, narrow strip of plastic upon which patterns can be written and fi-om which the patterns can be read back. 

Machines, processes, people, and whole situations are stored in the brain and can be recalled at will, like files from the hard disc of a computer. This cuts down enormously on the amount of information about any scene which an individual needs to take in in order to perceive and understand it. But where the real world differs from the expectation, problems occur. This is roost often the case with situations which go against population stereotypes, for example a machine on which moving a lever downwards turns it off. Other population stereotypes are red for danger and stop, clockwise turns the volume up or shuts the valve. These examples are very widely shared, but in other cases stereotypes for one population may contradict those held by others, e.g. you turn the light on by putting the switch down in Britain but by pushing it up in the USA and parts of Europe. 

Letters that previously stood for words such as "disc," but now do not stand for three words. Taken together, they refer to a standard for digitally encoding music and video, and storing it in a CD-configured plastic medium. (Note that "disc" is spelled with a "c" when referring to music storage, but with a "k" if used for other purposes such as computer hard drive memories.)... 

Besides using computers to help in their research, what are the possible interests of physicists in computers and computational processes Even this question could lead to different routes. Researchers could, for instance, attack on the material science side, studying the physical properties of bulk semiconductor materials, the basic stuff from which chips are made of, or studying the magnetic materials, the basic stuff hard-discs are built from. One could take the route of the so-called nanoscience and nanotechnology and exploit the ultimate limits of miniaturization of computer components, down to the molecular size. Yet, we can take an entirely different route, and ask for very fundamental questions about computers and about computation. One could ask, for instance, what is the minimum amount of energy and time necessary to flip a bit of information, or whether it is possible to perform computation without any energy expenditure at all. Or still, what is the limit... 

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