SEEMANT INSTITUTE OF TECHNOLOGY, PITHORAGARH A Constituent Institute of Uttarakhand Technical University A Seminar Report On “HOLOGRAPHIC DATA STORAGE” Submitted to- Submitted By- Mr. Jaydeep Kishore Brijesh Kanyal Mr. Satendra Kumar 111190101009 ACKNOWLEDGEMENT I thank GOD almighty for guiding me throughout the seminar. I would like to thank all those who have contributed to the completion of the seminar and helped me with valuable suggestions for improvement. I am extremely grateful to Mr. Jaydeep Kishore, for providing me with best facilities and atmosphere for the creative work guidance and encouragement. I would like to thank my coordinator and guide, Mr. Satendra Kumar, for all help and support extend to me. I thank all Staff members of my college and friends for extending their cooperation during my seminar. Above all I would like to thank my parents without whose blessings; I would not have been able to accomplish my goal. INDEX 1. Abstract 2. Introduction 3. Different types of data storage systems 3.1. Magnetic data storage system 3.1.1. Magnetic disk 3.1.2. Floppy disk 3.2. Optical data storage system 3.2.1 CD technology 3.2.2 DVD technology 4. Holographic data storage systems 4.1. Theory behind holographic data storage systems 4.2. Advantages of holographic data storage systems 4.3. Working 4.3.1. Spatial Light Modular (SLM) 4.3.2 The components involved 4.3.3. Writing 4.3.4. Reading 4.3.5. Multiplexing 4.3.6. Errors 4.4. Holographic Versatile Disk 4.4.1. Some features 4.4.2. Disk structure 4.4.3. Limitations of HVD 4.4.4. Comparison of HVD 5. Future development and challenges 6. Conclusion 7. References ABSTRACT This paper provides a description of different type of data storage systems along with examples. Later it introduces the concept holographic data storage system (HDSS), a three dimensional data storage system which has a fundamental advantage over previously mentioned conventional read/write memory systems. The theory behind HDSS and working is seen, which is followed by some advantages of HDSS with respect to other systems are discussed. Later the working is seen which discusses reading, writing and some multiplexing techniques. Then Holographic Versatile Disk (HVD) is discussed. The future development and challenges of holographic memory is then presented, followed by conclusion. 2. INTRODUCTION It is estimated that until now people have produced more than 5 exabytes (5 billion gigabytes) of data, the majority of which is in digital form. Since this figure is always growing and analogue media is constantly being converted to digital, new methods of storing this data are needed. Currently the two main storage methods i.e. magnetic and optical are just about keeping ahead of these needs; unfortunately this is not always going to be the case. Holographic data storage is a potential replacement technology in the area of high capacity data storage currently dominated by magnetic and conventional optical data storage. 3. Different types of Data storage systems They are • Magnetic Data storage • Optical data storage 3.1. Magnetic data storage Magnetic storage and magnetic recording are terms from engineering referring to the storage of data on a magnetized medium. Magnetic storage uses different patterns of magnetization in a magnetizable material to store data and is a form of non-volatile memory. Some of the major storage devices that comes under magnetic data storage systems are • Magnetic disk • & Floppy disk 3.1.1 Magnetic Disk: Hard disks were invented in the 1950s. They started as large disks up to 20 inches in diameter holding just a few megabytes. Magnetic disk is a plastic disk coated with magnetic material and used for storing computer programs and data as a series of magnetic spots. Most computers contain a hard disk unit for general storage. Hard magnetic disks can store larger amounts of data and come in cartridges that slot into a special drive unit. Structure and working On a hard disk (magnetic disk), data is stored in the magnetic coating of the disk‟s platters. The platter is a flat disk of either alloy or glass, with a spindle at the centre. Modern platters generally have a diameter of 3.5” in desktops or 2.5” in laptops, although smaller drives are available for devices that require a micro-drive. The spindle is rotated by an electric motor, and this cause the platter to spin. The speed at which the platter spins is measured in RPM and a higher speed is usually reflective of a higher performance, disk, in terms of data writing and reading. The magnetic media holds the binary data as with tapes and floppy disks. The data is read from the surface of the platter by a set of „heads‟ which are fixed so that they can only move between the centre of the platter and the outside edge. The heads are held just above the magnetic media by actuator arms that facilitate this movement across the disk‟s platter surface. The heads are not designed to touch the platter surface as physical contact can cause damage to the magnetic media. Each platter has a top side and an underside, and there is usually a head for both. Therefore, a hard disk drive with 5 platters would have 10 heads. When the disk is not in use, the heads are „parked‟, usually at the outside edge of the platter. Data in the magnetic media is organized into cylinders - concentric tracks on the media that are further divided into sectors. A sector is the smallest allocatable logical unit on a drive and usually, but not always, is 512 bytes in size. Next, the drive moves the heads over the appropriate track on a platter. The time it takes to move the heads is called the seek time. Once over the correct track, the drive waits while the platters rotate the desired sector under the head. The amount of time that takes is called the drive's latency. The shorter the seek time and latency, the faster the drive can do its work. When the drive electronics determine that a head is over the correct sector to write the data, the drive sends electrical pulses to that head. The pulses produce a magnetic field that alters the magnetic surface of the platter. The variations recorded there now represent the data. Reading data complements the recording process. The drive positions the read portion of the head over the correct track, and then waits for the correct sector to orbit around. When the particular magnetic specks that represent your data in the right sector and track pass under the read head, the drive's electronics detect the small magnetic changes and convert them back into bits. Once the drive checks the bits for errors and fixes any it sees, it sends the data back to the operating system. Below is the diagram of the hard disk with platters, spindle and the head. 3.1.2 Floppy disks Floppy disks are smaller, simpler, and cheaper disk units that consist of flexible, removable, plastic, diskette coated with the magnetic material. The diskette is enclosed in plastic jacket, which has an opening where the read/write head makes contacts with diskette. A hole in the centre allows a spindle mechanism in the disk drive to position and rotate the diskette. Information recorded on floppy disks by combining the clock and data information along each track using Manchester encoding. Disks encoded in this way are said to have single destiny. The main features of floppy disks are small physical size and low cost. But this is offset by smaller storage capacity longer access time and higher failure than hard disk. The floppy disks have been superseded by the emergence of rewritable compact disks having higher capacities. 3.2. Optical data storage Today's meaning of optical data storage refers to storage systems that use light for recording and retrieval of information. Optical recording systems potentially have much greater reliability than magnetic recording systems since there is a much larger distance between the read/write element and the moving media. Therefore, there is no wear associated with repeated use of the optical systems. Another advantage of the optical recording systems over the best performing magnetic recording systems - hard drives - is their removability. The main disadvantage of optical storage when compared to magnetic is slower random data access. This partially comes from the design of the relatively large (and heavy) optical heads. Optical drives of all kinds operate on the same principle of detecting variations in the optical properties of the media surface. CD and DVD drives detect changes in the light intensity, MO drives - changes in the light polarization. All optical storage systems work with reflected light. Some of the major optical data storage technologies are • CD Technology. • DVD Technology. • Blue ray disk Technology. • Holographic data storage technology. 3.2.1 CD Technology: The first generation of CD was developed by sony and Philips corporations, for audio systems. To provide high quality audio production and reproduction, 16-bit samples Of the analog signals are taken at 44100 samples per second. The CDs were required to hold at least an hour of music. Structure of a CD A CD is a fairly simple piece of plastic, about four one-hundredths (4/100) of an inch (1.2 mm) thick. During manufacturing, this material is impressed with microscopic bumps arranged as a single, continuous, extremely long spiral track of data. Latera thin, reflective aluminium layer is sputtered onto the disc, covering the bumps. The CD can store up to 600Mbs of data.