White 1Jesse WhiteMrs. MaxwellBritish Literature30 October 2011 The Turing Machine and Data Storage So just to make sure that everyone is clear on this: computers are everywhere. Let therebe an extra emphasis on everywhere. In your clock, in your phone, in your car, in your coffeemaker, in your television, in your thermostat, and in your oh so precious iPod are computers.There is almost no place with human habitation that you cannot find some form of computer.These machines are fantastic. They are all unbelievable, and they are all based off of one simpleidea: an idea of a machine and an infinite tape. But before anything else is discussed, the issue ofwhat exactly a computer is should be settled. Well the term computer is not new at the very least. It was actually used as early as 1613to describe someone that performs calculations. The meaning grew as machines were developedthat performed simple calculations and eventually was only applied to such machines. Obviously,this is not the current usage of the term. What computer now generally refers to is any devicethat is considered a “universal Turing machine”, which is any machine that mimics the “TuringMachine”. This term, coined by one Alan Turing, is an idea, one of an imaginary machine thatmanipulates a chain of symbols off of an infinite tape, storing only one symbol at a time, withthis symbol adjusting the behavior of the machine. The machine is also able to move itself alongthe tape freely in order perform its functions. While such a strange machine seems a far cry fromour modern digital computing, they are truly one and the same. Machine language ismanipulated on magnetic disks and the language is stored in Random Access Memory, thus
White 2modifying the function of the Central Processing Unit which adjusts the language that is storedon the magnetic disks. The process is identical, but the names are different. This is our digitalcomputer. The next item up for examination, extrapolation, and general discussion is data storage,that wonderful “infinite tape” of the Turing Machine. It is arguable that this is the most importantcomponent of the machine, but most importantly about it, is the wide variety of types of datastorage. There are four main categories of methods of data storage: primary data storage,secondary data storage, tertiary data storage, and off-line data storage. Primary data storage is thefastest type of data storage, as it should be, seeing as how it being what it is means that it isdirectly accessible by the CPU. Secondary data storage is any media that is not directlyaccessible by the CPU, but it is still able to be accessed typically through input/output channels.Tertiary storage media that requires the media be physically loaded into a drive, but is donewithout human interference. The final method of data storage is off-line data storage. This typeof storage is when data is stored in a typical secondary or tertiary storage device, but a human isrequired to physically load the device or media. Modern primary data storage is fast. It is fast, but it is volatile; volatile meaning thatwhen the machine is powered off, all data stored on the device is lost. As of now, there are threelocations where primary storage is on in a machine. The first is inside the CPU itself, which iscalled the processor register. There are typically multiple processor registers and each one’s datastorage capacity is ridiculously small. Despite their size however, the processor registers are theabsolute fastest methods of data storage, and are used to hold commands that the CPU usesdirectly in order to have instructions on how manipulate other data. After the processor registersare the processor caches. There are typically three caches nowadays, with caches one two and
White 3three successively larger and slower than the last, just as the entire data storage hierarchy does.While not quite as fast as the effectively instant processor registers, the processor caches areblazingly fast. The final type of primary data storage is consistently called the “main memory”.This storage is nowhere near as fast as the other forms of primary storage (meaning the measureof time is now in milliseconds instead of nanoseconds). However, despite its relatively slowspeed, main memory is also ridiculously large when compared to the others. After the mainmemory comes an entirely different type of data storage, the secondary storage, at which point,humans are actually capable of realizing that the transfer of data is not instant. Of the types of secondary data storage, there are actual tapes that are magnetized, opticalmedia, flash memory, and disks that are magnetized. And each of these has their own uses. Thefirst up to plate is the magnetized tape. Now used primarily in things such as credit cards, thismethod of data storage has been used in floppy disks and cassette tapes. It was the first methodthat was used to store data in a digital format being followed by the magnetized disk which isknown as the hard disk drive or HDD. The HDD consists of multiple spinning platters and iscurrently the method capable of storing the most data per device. A relatively fast method of datastorage, the HDD is bested only by the flash memory in the category of read/write speeds. Flashmemory is a magical device that manages to hold an electrical charge in floating-gate transistors.It is really incredibly confusing, so Mr. Clarke’s third law of “any sufficiently advancedtechnology is indistinguishable from magic” is most definitely applicable in this situation. But itis basically a bunch of metallic cells that are insulated by resistors giving them the ability to holda charge for years. As with any emerging technology, the cost of this method of data storage ishigh. However it is the method that offers the absolute best performance when it comes to speed.Along with being incredibly fast, it also is essentially unaffected by environment conditions,
White 4makes no sound, consumes one half to one third of the power of the average HDD, is unaffectedby magnetic interference, is able to read and write to multiple flash chips simultaneously, and issmaller and lighter than the HDD. The most significant drawbacks of flash memory being that ithas a limited number of read/write cycles, its performance degrades as cells are used, and thatdata already written to flash memory is incredibly difficult to truly delete due to the algorithmsthat are implemented to combat the dilemma of possessing a limited number of read/write cycles.The final type of secondary data storage is optical media. Optical Medias are forms of secondarydata storage that utilize lasers to read data that is typically stored on a disc. CDs, DVDs, and BDsall contain pits (depressions) and lands (flat areas) in a metallic layer. When a disc is read, alaser detects the sequence of pits and lands in that metallic layer which are understood by thedevice as true and false, zero and one, binary code. Optical Medias are an incredibly reliableform of data storage as they will continue to be able to be read until someone with a less thanaverage intelligence decides that it would be a good idea to put it in the microwave or write allover the protective polycarbonate layer, or be an even bigger moron and break the disc in halfaltogether. Point is, the disc should be readable indefinitely. This reliability is great forarchiving purposes. Another high point of the media is its affordability. Due to the media’s highaffordability, it has for quite a while been used as the primary mode of secondary data storage forthe entertainment world. However due to recent advancements in data transfer via the Internet,the media has begun to die out for its uses in data transfer, and is now primarily used for reliabledata archival. Tertiary storage is technically a type of data storage, but it is really only used for archivalpurposes, such as in the library of a university or in a jukebox or something. All it means is thatwhile the processor technically has access to the data, a device must be physically mounted by
White 5some kind of robotics before it can be accessed. This is very similar to off-line storage, which isthe final type of data storage. The only differences between tertiary and off-line storage is that ahuman must mount the device instead of the CPU using a robotic device to mount the storagedevice. Also of note about tertiary and off-line storage devices is that despite its inclusion insecondary data storage, optical storage is typically used in a manner that would have it fall undertertiary or off-line data storage. All four types of storage can be considered to be the “infinite tape” of Turing’s machine.Turing’s machine is the basis for every digital device that exists today, and every single one ofthose devices uses one type of data storage device or another. So the gist of everything isessentially that there is a lot of data in this world, that data needs to be held somewhere,somehow, and that the universal Turing machine and all of the forms of data storage manage tohold the majority of humanity’s information.
White 6 Works CitedJacobson, Carol. (1998) Fundamentals of Data Storage NCGIA Core Curriculum in GIScience, 6 Oct. 1998. Web. 30 Oct. 2011 <http://www.ncgia.ucsb.edu/giscc/units/u037/u037.html>.Lyons, Bob. Introduction to Turing Machines, Unidex Inc, 4 Oct. 2008. Web. 30 Oct. 2011 <www.unidex.com/turing/tm_intro.htm>.Copeland, Jack. Bio of Turing, The Turing Archive for the History of Computing, Jul. 2003. Web. 30 Oct. 2011 <www.alanturing.net/index.htm>.