Requirements for removable media storage devices (RMSDs) used with personal computers have changed significantly since the introduction of the floppy disk in 1971. At one time, desktop computers depended on floppy disks for all of their storage requirements. Even with the advent of multigigabyte hard drives, floppy disks and other RMSDs are still an integral part of most computer systems, providing.
Transport between computers for data files and software
Backup to preserve data from the hard dive
A way to load the operating system software in the event of a hard failure.
Data storage devices currently come in a variety of different capacities, access time, data transfer rate and cost per Gigabyte. The best overall performance figures are currently achieved using hard disk drives (HDD), which can be integrated into RAID systems (reliable arrays of inexpensive drives) at costs of $10 per GByte (1999). Optical disc drives (ODD) and tapes can be configured in the form of jukeboxes and tape libraries, with cost of a few dollars per GByte for the removable media. However, the complex mechanical library mechanism serves to limit data access time to several seconds and affects the reliability adversely.
Most information is still stored in non-electronic form, with very slow access and excessive costs (e.g., text on paper, at a cost of $10 000 per GByte).
Some RMSD options available today are approaching the performance, capacity, and cost of hard-disk drives. Considerations for selecting an RMSD include capacity, speed, convenience, durability, data availability, and backward-compatibility. Technology options used to read and write data include.
Magnetic formats that use magnetic particles and magnetic fields.
Optical formats that use laser light and optical sensors.
Magneto-optical and magneto-optical hybrids that use a combination of magnetic and optical properties to increase storage capacity.
The introduction of the Fluorescent Multi-layer Disc (FMD) smashes the barriers of existing data storage formats. Depending on the application and the market requirements, the first generation of 120mm (CD Sized) FMD ROM discs will hold 20 - 100 GigaBytes of pre -recorded data on 12 — 30 data layers with a total thickness of under 2mm.In comparison, a standard DVD disc holds just 4.7 gigabytes. With C3D’s (Constellation 3D) proprietary parallel reading and writing technology, data transfer speeds can exceed 1 gigabit per second, again depending on the application and market need.
Technologies
During the writing process small magnetic domains are written, the magnetic fields of these domains are detected during the read process. The information can be overwritten indefinitely. The areal density of magnetic recording has grown by approximately 60% per year during the last decade. Devices with 10 Gbit/sqi are currently in production, 3OGbit/sqi have been demonstrated. However, there appears to be a limit - “the super paramagnetic limit where the magnetic domains become unstable, thus limiting further growth in the areal density achievable. In optical disc drives (ODD) such as CD, DVD and MO, light from a semiconductor laser is focused onto the storage layer to perform writing/reading. The storage layer is protected through the disc substrate or a thick overcoat, making this technology well suited for removable media. The achievable storage density is determined by the size of the recording spot, which in turn is determined by the wavelength of the laser light, resulting (with current 650 nm red lasers) in a maximum a real density of 5 bits/micrometer 2. Advances in laser technology leading to utilization of 480 nm blue lasers will increase this density four-fold. Advanced optical techniques using magneto-optic MSR,MAMMOS, HYBRID, near-field and super-RENS technologies are expected to achieve areal densities of approximately 50 bit/ sqi over the next ten years, making capacities of up to 100 GByte per disk possible on CD/DVD sized 120-mm diameter, 1.2-mm thick disks.These systems will need to use blue lasers, complex-structured media and extremely sophisticated optics and mechanics. Areal densities of various techniques are shown in Figure 2.
Volumetric Recording
As can be seen from the above, the storage density of media using current HDD and ODD technologies is limited due to the need to store data within a thin layer near the surface of the media.
Holographic Storage
With the advent of lasers in the 1960s, storage in 3D has been proposed by using holographic techniques. However, attempts at commercialisation have so far failed, primarily due to lack of suitable storage materials for media manufacturing.
Multi-layer Storage
In a multi-layer card or disc, several layers are integrated into the media, separated from each other by distances as small as 15 micrometers. A recording laser beam is focused onto one layer at a time writing and reading the layers separately.
Reflective Multi-layer
The concept of multilayer optical discs has been proposed by Philips and IBM, and has been demonstrated up to several layers. The DVD is an implementation of this concept with two layers. However, for many layers the coherent nature of the probing laser beam causes interference scatter and intra-layer cross talk—the combination of which results in a signal that is degraded to unacceptable levels. Following its research into the feasibility of producing a 6-layer optical disc, IBM announced that it would not proceed to production of such devices due to the many difficulties involved in its implementation and thus commercialisation.
Fluorescent multilayer
The concept of multi-layer, fluorescent cards/discs (FMD/C) is a unique breakthrough; solving the problems of signal degradation. Here the storage layer is coated with a fluorescent material. When the laser beam hits the layer, fluorescent light is emitted. This emitted light has a different wavelength from the incident laser light—slightly shifted towards the red end of the light spectrum—and is incoherent in nature, in contrast to the reflected light in current optical devices. The emitted light is not affected by data or other marks, and transverses adjacent layers undisturbed. In the read-out system of the drive the light is filtered, so that only the information-bearing fluorescent light is detected, thus reducing the effect of stray light and interference.
Theoretical studies, confirmed by experimental results, have shown that in conventional reflection systems the signal quality degrades rapidly with the number of layers .In fluorescent read out system, on the other hand the signal quality degrades much more slowly with each additional layer (see below). Research has shown that media containing up to a hundred layers are currently feasible, there by increasing the potential capacity of a single card or disk to hundreds of Gigabytes. Use of blue lasers would increase the capacities to over 1 Terabyte.
STATUS OF DEVELOPMENT
A principal obstacle to the development of small portable appliances with large data storage capacity is the lack of inexpensive small size memory carriers that can store Gigabytes of information in a media allowing fast data transfer rates. Constellation 3D’s fluorescent multi-layer technology enables the production, in a wide variety of form factors, of storage media satisfying these criteria.
Media
The FMD/C media consist of several plastic (polycar-bonate) substrates bonded together.The substrates contain surface structures (“pits”) that a re filled with a proprietary fluorescent storage material.
A major design goal in the development of CD/DVD replacements using this technology was to allow a simple and cost-effective upgrade for existing manufacturers of optical devices. FMD technology enables the use, with only relatively minor changes (such as impregnation with flourescent materials), of existing components and processes from high volume products such as CDs/DV D s, and avoids the need for new infrastructure for media and drive production. The number of process steps per layer is actually reduced, because a reflective metallic layer is not required. For the individual layer of a multilayer disc, metal stampers containing the digital content are produced in a mastering process that is similar to CD or DVD processes. For FMD/C, two replication processes have been developed:
1. Hot-embossing: In this process, thin sheets of polycarbonate are embossed on both sides with the metal stampers at elevated temperatures. The embossed pits are then filled with the fluorescent dye. After the dye is cured, the individual sheets are bonded together under pressure, resulting in a storage media having multiple layers. Figure 4 shows a 7-layer media.
2. Photo-polymerisation (2P) process: In this method, layers are replicated one after the other the formation of “thin replicas”. This technology has been demonstrated for up to ten layers.
Fluorescent Material
Perhaps the most critical component of the storage media is the fluorescent material that converts the incident (incoherent) laser light into incoherent fluorescent light. The materials and associated drives for read-only cards and discs (ROM) are currently the most mature FM technology. Recordable materials and associated drives have also been developed and demonstrated, and improvement of this FM technology continues. FMD/C write/read technology based on proprietary photochromic substances has been demonstrated in Constellation 3D’s laboratories during write! read / erase / re-write experiments.
