A millenium or a microsecond - recording the extremes.
THE SQUIRREL MENTALITY
People, like squirrels, like to save stuff. The squirrel generally has an excuse; he needs those nuts he's buried to survive the winter. Mankind would also like to tuck away every word written in every book or magazine, every picture or drawing whether produced on Earth or sent back from the outer limits of the galaxy, every financial transaction and every fleeting assembly of digital data residing, even temporarily, on the Internet and on and on. This "stuff" is archived on big storage systems and is not the subject of this article (however, if your interest is in "big," see Linda Kempster's "Where Storage Will Be in 2000," JED, August 1996, p. 44).
And the proprietors of these archives would like to store their treasures for a long time. For example, the Norwegian Legal Deposit Act of June 9, 1989, established the Norwegian National Library as the responsible agency for acquisition, registration and longtime archiving of various documents in electronic form. The aim of the library is to store electronic journals, newsgroups and other open conference systems, electronic book manuscripts, documents available through the World Wide Web or Gopher and other electronic texts which are openly distributed on CD-ROM or via data networks. In addition, the collection will house on-line or off-line databases which are publicly available as text, statistics, reference data, images and, in practice, anything which is retrievable from an on- or off-line database system. And finally, it must capture publicly available audiovisual material, i.e., television and radio broadcasts, films, musical records and more.
Ambitious, yes...but here comes the kicker. The library would like to preserve the information for at least 1,000 years. It is conceded that even if the digital storage media could hold the data for a 1,000 years, one would have to face the problem of finding a computer able to understand the electrical interface of the storage device, the physical format of the storage media and the semantic format of the data itself.
MAGNETICS STILL THE WAY TO GO
While most phenomena are analog in nature, the resulting data may be registered in analog or digital form. Analog recording is embodied by the familiar audio tape recorder and a host of photographic techniques used to capture visual data. The recording of analog data in digital form, however, often simplifies data processing, manipulation, error correction and storage. The binary recording process begins with analog-to-digital (A/D) data conversion. The resulting digital data can be stored in many ways, including as magnetic domains on disks or tapes, as electrons and "holes" (the absence of electrons) in solid-state memories and as changes of surface reflectivity on optical media.
By far, the most mature medium is magnetic storage. Magnetic recording is divided into two principal classes - those using rigid disks and those employing flexible tapes usually pre-loaded into removable cassettes or cartridges. The first commercially available videotape, an open-reel format, was introduced in 1957 by the 3M Co. This was replaced by the much more convenient Beta format, 0.5-in.-wide tape in a hard plastic cassette. In the infancy of video cassette recorders, Beta was the popular, and basically the only, tape format available. Later VHS arrived on the market; the two formats coexisted for a time, but finally the VHS format evolved as the standard. However, the simplistic days of two tape formats are over.
THIS YEAR'S WUNDERKIND
Flexible tapes, in general, record data by drawing the tape over fixed read/write (R/W) heads. There may be multiple R/W gaps in a fixed head, but basically all tape systems record and access data in a serial manner. The IBM 3490E, introduced in 1991, writes 36 tracks on a 0.5-in. tape. Helical scan technology, introduced by Ampex Systems Corp. (Redwood City, CA) in 1961, decoupled the tape track density from the number of heads in the drive by mounting the R/W heads on a drum, called a scanner, that rotates at high speed. The tape is moved very slowly across the scanner, which is mounted at a slight angle to the tape path. This causes the data to be recorded on diagonal stripes across the tape.
Over the last few years, a new tape technology has arrived on the scene. The new "kid on the block" is digital linear tape (DLT). Starting as a proprietary technology belonging to Digital Equipment Corp. (Maynard, MA), DLT provides high-capacity, high data-transfer speeds and highly reliable recording. Converts are being drawn to DLT because of the volume of data it can handle. With a capacity of up to 20 GB, or 40 GB compressed, and a data-transfer rate of 1.5 MB/sec, DLT provides as much as four times the capacity and three times the speed of traditional tape products.(*)
DLT technology segments the tape into parallel horizontal tracks and records data by streaming the tape medium across a single stationary head at 100 to 150 in./sec during read/write operations. This approach is a dramatic contrast to the diagonal striping and rotating drum head of traditional helical-scan technology. DLT technology results in a more durable drive and a more robust medium. DLT drive heads have a minimum life expectancy of 15,000 hr under worst-case temperature and humidity conditions, and the tapes have a life expectancy of 500,000 passes.
With the addition of DLT, the selection of recording formats grows still larger. A very brief overview of some of these options includes:
* Cassettes: Based upon widely used audio cassettes, this 0.125-in.-wide tape is available in native (unformatted, uncompressed) capacities of 60 MB to 600 MB.
* 4-mm: This tape format, developed for digital audio tape (DAT) cassettes, has storage capacities in the 1.2- to 5-GB range and can transfer data at about 180 kB/sec.
* Quarter-Inch Cartridges (QIC): The 0.25-in. minicartridge is a popular choice for high-volume PC backups. The 3.5-in. form factor cartridge can have multiple recording tracks with capacities up to 13 GB. Travan (3M[TM]), produced by Imation (Oakdale, MN), uses a novel design and QIC technology to produce a family of cartridges with uncompressed capacities ranging from 400 MB (TR-1) to 10 GB in the TR-5.
* 8-mm: Storage products based upon helical-scan 8-mm video camera technology were first introduced by Exabyte (Boulder, CO) in 1987. The initial offering, the EXB-8200, had a capacity of 2.3 GB. Exabyte is currently shipping its new Mammoth drive that stores 20 GB native.
* 3480/3490: Introduced by IBM in 1985, the 3480 tape cartridge and drives retained the 0.5-in. format but increased capacity to 200 MB by writing data in 18 parallel tracks. Data compression was introduced on 3480 drives as an option, increasing the effective cartridge capacity from two to five times, depending upon the nature of the data. The 3490, offered in 1989, made data compression standard on the product. The 3490E, appearing in 1991, doubled the 3490 cartridge capacity by writing 36 tracks on the tape, 18 in a forward direction and 18 in reverse. By increasing the tape length using a thinner tape, a base capacity of 800 MB per cartridge was achieved without data compression.
* VHS 0.5-in.: The first product to use, the 0.5-in. T-120 cassette was Honeywell's Very Large Data Storage (VLDS) system. This format was used in a helical-scan instrumentation recorder which could store up to 5.2 GB per channel. Either one or two channels were available. This tape format is now used by Metrum Information Storage in the improved ST-120 cassettes with 10.4-GB capacity and ST-160 at 18 GB.
* 19-mm: Packaged in three sizes of cartridge shells, the DST line systems introduced by Ampex Systems Corp. have capacities ranging from 25 GB on a small cartridge to 165 GB on the large. When used with the high-speed helical scanner of the DST 600 tape drive, two sets of R/W heads produce a sustained transfer rate of 15 MB/sec.
The native capacities and data transfer rates of several of these formats are found in Figure 1.
WHAT'S OUT THERE TODAY?
With the multitude of tape formats available today and the even greater selection of data recorders that use these tapes, the selection of a recorder is challenging, to say the least. Not only are storage capacities and writing speeds of concern, but the operational environment, preservation requirements and the availability of compatible playback units in the future must come into the procurement equation.
Precision Echo, Inc. (Santa Clara, CA), a subsidiary of Diagnostic/Retrieval Systems, Inc., is the source of recorders designed to meet the rigid requirements of systems in the field. The AN/USH-42 Mission Recorder/Reproducer Set is a two-channel system that is Mil-E-5400 qualified. Suitable for the US Navy's A-6E, S-3, F-14 and F/A- 18 tactical aircraft, this unit features an 111-min recording duration on VHS cassettes. A pair of compact airborne video tape recorders, the WRR -812 and WRR-818 are offered for airborne and ground imagery recording. The WRR-812, a small, 0.22-[ft.sup.3], 8-lb package, and the WRR-818, a 0.1-[ft.sup.3], 6-lb unit, are designed to meet Mil-Std-810E requirements. The units are able to record for 150 min on the 8-mm Sony P6-150 cassette and are particularly attractive for cockpit or unmanned air vehicle (UAV) recording operations.
The CY-8000, a product of Cybernetics (Yorktown, VA), also uses an 8-mm tape in the compact 3.5-in. form factor cassette. The unit's standard capacity is 25 GB on a single tape at 3 MB/sec. Optional data compression can boost capacity up to 125 GB.
Introduced in October 1996 by Metrum (Littleton, CO), the Model 32HE [ILLUSTRATION FOR FIGURE 2 OMITTED] is the latest in a line of digital recording products based on the Inter-Range Instrumentation Group (IRIG) standard 0.5-in. tape format. Conforming to Mil-Std-5400T vibration standards, this flight-qualified, hostile environment recorder uses a helical-scan mechanism. Features of this unit include a 0- to 32-Mb/sec variable data rate and a 57-min recording time at the maximum stream rate. Weighing less than 40 lb, the 32HE is expected to find use in a variety of test applications on fixed-wing, rotary-wing, UAV, tank and commercial aircraft. While Metrum's cassette tape-based digital data recorders have been used in a variety of military flight data acquisition applications for almost a decade; Perry Moss, Metrum's marketing manager, stated, "This is the first time we've designed and manufactured a fully ruggedized version of our recording technology."
The fully ruggedized AE5800, a wideband analog data recorder produced by Avalon Electronics Ltd. (Dawsonville, GA), records 8-MHz data for up to 1 hr on a standard ST-120 S-VHS cassette. Housed in an ATR-size enclosure, the self-contained 7.4 x 10.2 x 18.4-in., 23-lb unit can be mounted in a customized ARINC 404 tray for mil-spec applications. When appropriately mounted, the AE5800 operates at full Mil-Std-810E vibration specifications. Physically similar to the AE5800, the AE5720 records up to eight asynchronous digital data streams. Optional features include a 6-hr "extended mission" capability and a 0.5- to 4-times time-base compression/expansion capability.
Designed for on-board and ground-based EW, radar and communications monitoring applications, Avalon's AE3120HW extends the analog bandwidth of S-VHS recording to 12 MHz. The extensive use of surface-mount technology results in a size reduction of 65% compared to previous systems, allowing two units to be mounted side by side in a standard rack. To satisfy multichannel intelligence-gathering requirements, a technique for synchronizing several AE3120HW units to better than 50 nsec has been developed. A typical four-unit installation [ILLUSTRATION FOR FIGURE 3 OMITTED] occupying only 20% of the volume of a conventional IRIG system can capture up to 24 separate wideband channels continuously for several hours.
The GEMINI, an S-VHS unit for rugged analog and digital applications, is a product of Penny & Giles Data Systems (Wookey Hole, England). The recorder's 8-MHz analog bandwidth covers a wide range of telemetry, EW, communications intelligence and signals intelligence applications. Remote-control connectivity is provided via RS-422, IEEE-488 and TTL ports in the 0.6-[ft.sup.3], 21-lb unit [ILLUSTRATION FOR FIGURE 4 OMITTED].
A new entry, the DIR-1000H, has joined the Sony Electronics Inc. (Montvale, NJ) DIR-1000 product line. Using a 19-mm tape format, the 1000H succeeds in doubling the 256-Mb/sec data rate of the DIR-1000. To achieve 512 Mb/sec, the 1000H doubles, to 32, the number of number of record and playback heads placed on the rotating drum. Recording capacity is 770 Gb on a large cassette and 330 Gb on the medium-sized cassette.
In a 0.5-in. tape format, Sony's ADI-1150 uses smoother tape surfaces and advanced lubricants to provide a 15-Mb/sec transfer rate (20 Mb/sec in bursts). When used with large, 52-Gb cassettes, the unit is capable of recording more than 58 min of data at maximum transfer rates.
Travan format is used in the latest Hewlett-Packard (Pale Alto, CA) tape backup units. The HP Colorado T4000s (internal) and T4000es (external) models combine Travan minicartridge technology and SCSI-2 performance [ILLUSTRATION FOR FIGURE 5 OMITTED]. The units have a 4.0-GB native capacity and burst transfer rates of up to 514 kB/sec.
An ATR enclosed data acquisition and recording system is offered by Racal-Heim GmbH in Germany (US contact in Irvine, CA). The DATaRec D4 uses DAT media to record 4 Mb/sec for two hours. The unit, housed in a compact and rugged 1/2 ATR enclosure, has been used for a number of aerospace and defense applications. Built-in vibration isolaters provide error-free operation in harsh environments up to Mil-Std-810C specifications. The D4 supports multiple digital and analog inputs and outputs for Mil-Std-1553 buses, ARINC 429 buses, serial and pulse code modulation (PCM) data and up to 40 channels of analog signals.
The inherent ruggedness of the DLT technology and its ability to perform well in harsh environments has signaled the start of a migration in the direction of this 0.5-in. tape media. The Racal-Heim DATaRec-D12, a derivative of the company's D4 system, uses DLT cartridges and is housed in a 3/4 ATR enclosure. The 0.5-in. tape, contained in a 4.1 x 4.1 x 1-in. cassette, can record for 220 min at a 12-Mb/sec data rate. The longitudinal DLT recordings are stored on 128 serpentine tracks (64 pairs).
In the second half of 1996, Datatape Inc. (Monrovia, CA) released its MARS-II and MARS-II-L DLT-based recorder/reproducer systems. The MARS-II has a two-unit configuration [ILLUSTRATION FOR FIGURE 6 OMITTED]. The mission-programmable electronic unit and the actual recorder weigh less than 50 lb and are both packed into 1,442 [in..sup.3] The system can record eight completely asynchronous, electronically configurable channels of PCM or Mil-Std-1553B data, in addition to one channel for IRIG time code data and one channel for voice annotation. The MARS-II-L is a laboratory version of the MARS-II. The -L combines the functionality of the MARS-II into a single unit with an optional second drive for data duplication.
The DLT format is also used in the Hewlett-Packard SureStore DLT30e and DLT40e backup units. These drives are capable of storing 15 and 20 GB native, respectively, with sustained transfer rates of up to 1.5 MB/sec for the 40e unit.
WHERE IS TECHNOLOGY GOING?
In this article and its sidebars, we have discussed the more traditional storage medium (magnetic), as well as some emerging technologies. We will doubtless be revisiting many of these approaches in the foreseeable future. But some of the more exotic (bizarre?) recording media discussed at the Fifth NASA Goddard Conference on Mass Storage Systems and Technology held in 1996 at the University of Maryland may require a bit more development before we will be writing about them on these pages. Included in this group might be storage in protein bacteriorhodopsin, the living scum (Halobacterium halobium) found off San Francisco Bay, and multiwavelength storage using strands of human DNA molecules.
* A lower case b is used to indicate a bit of data, either a "one" or a "zero." Data rates are often indicated as bits per second, b/sec. The capital letter B is used as an abbreviation of "byte," which is usually taken to represent an eight-bit word. Memory capacities are customarily given in bytes. In computer and storage usage, the prefixes k for kilo, M for mega, etc., are often used as abbreviations for binary power rather than powers of 10; thus k, rather than representing 1,000, usually refers to [2.sup.10] or 1,028; while M, rather than being 1,000,000 represents [2.sup.20] or 1,048,576.
1. C. Bucholtz, "DLT: Tape's Future," LAN Times, December 8, 1995.
RELATED ARTICLE: Data Storage in Crystals
In November 1995, IBM started a $32 million holographic data storage project with a group of partners including GTE, Kodak, Rockwell, Stanford University and Carnegie-Mellon University. Termed the Holographic Data Storage System (HDSS), the technology calls for data to be stored holographically as "pages" of bits within an optical medium such as a crystal.
The holographic memory consists of a myriad of optical interference images recorded in a light-sensitive, usually erasable medium. To achieve high storage density, the images are multiplexed - that is, more than one image occupies the same volume within the crystal. To differentiate these images, subtle recording differences are used. These differences might include changing the reference angle of the optical components employed to produce the hologram, changing the wavelength of the laser light used or several other optical stratagems. Later, the inverse optical conditions will be used to reconstruct the hologram so that data can be optically or photographically read out.
Early results from experiments portend that holographic technology could be used to store 12 times as much data at the same cost as magnetic disk storage. Another goal of HDSS is a capacity of at least a terabit ([10.sup.12] bits) in the volume of a small coin Furthermore, because holographic storage promises input/output rates 10 times faster than its magnetic counterpart, data rates of 1 Gb/sec are within the realm of possibility.
But it is the technology's ability to perform searches in totally new ways that makes holographic storage so compelling. A search could be conducted by multiplexing all the stored pages into a single volume and simultaneously viewing all the material and determining which page most closely matches your search criteria. With rotating media such as magnetic tape storage, you're basically constrained to a serial type of reading.
The possibility of using "associate retrieval," a pattern-recognition type of approach for finding information, is also under consideration. For example, to locate information about a specific topic, a user could interrogate the holographic crystal to find the page with the digital pattern that most closely matched the pattern of the information being sought. Holographic data storage could lead to completely new ways of representing information.
RELATED ARTICLE: Solid, Solid State
An obvious approach to making high-reliability recorders for severe environmental applications is to have no moving parts. This is the approach used in solid-state memory recorders. In the past, high cost and limited memory capacity had restricted the use of this technology. But the situation is changing.
One embodiment of a solid-state recorder was recently demonstrated by the Fairchild Defense Division of the Orbital Sciences Corp. (Germantown, MD). The High-Speed Solid State Recorder (HSSR) culminated a two-year project to design and produce an all-solid-state recorder. In tests aboard a P-3C aircraft over Patuxent River Naval Air Station, MD, the HSSR was used to record and reproduce digital reconnaissance imagery. The unit is designed for an input rate of 240 Mb/sec and a capacity of 54 GB, with the ability to upgrade in the future as memory chip capacities increase.
An earlier version of the HSSR, the Solid-State Drive (SSD), with 240 MB of memory and an IDE interface, was initially deployed on F-14 aircraft equipped with the US Navy's Tactical Airborne Reconnaissance Pod System. The SSD served as an on-board memory cartridge.
RELATED ARTICLE: The Optical Scenario
Optical digital recording technology began in 1965 with a search for a better long-playing record by Battelle researcher James T. Russell. From Russell's ideas came 22 patents that contain the critical design elements of compact discs and CD-ROMs.
In this technology, information is recorded as a track of binary bits, or dots, each 1 [[micro]meter] in diameter. In comparison, a human hair is about 100 [[micro]meter] in diameter. The dots are recorded onto a flat photosensitive plate or card. In the playing mode, a laser light beam is scanned over the recorded media and a photodetector picks up the resulting patterns of light and dark, converting that binary information into an electronic signal. Computer circuits can now reconstruct the original signal to a form that can be played back through an ordinary television or stereo amplifier.
Currently, two types of optical recording media are commercially available - write-once-read-many (WORM) and rewritable magneto-optic (M-O), also known as CD-recordable (CD-R). WORM technology finds use in libraries and archives. Rewritable, or M-O, technology is used to record as well as play back digital data.
One company firmly committed to optical recorders is Mountain Optech, Inc. (MOI - Boulder, CO). MOI's ST-250 and ST-1000 lines of ruggedized multifunction optical drives have found application in several military systems. The ST-250 is a 3.5-in. disk able to store 230 MB at burst rates of up to 5 Mb/sec. The ST-1000, a 5.25-in. drive, has a data storage capacity of 1.3 GB.
Hewlett-Packard recently announced a family of CD-recorders, Its SureStore 6020 series: the 6020i, for internal computer use; the 6020es, a SCSI version; and the 6020ep, a parallel-port version. Data capacity on the larger 120-mm disk (5.25-in. form factor) is 680 MB native and 193 MB on the smaller 80-mm (3.5-in. form factor) disk. Transfer rates are up to 900 kB/sec reading and 300 kB/sec writing.
Meanwhile, Rome Laboratory (Rome, NY) is managing a $12 million Technology Reinvestment Project (TRP) designed to substantially increase the storage capacity of optical disks. The Short Wavelength Optical Storage Consortium, consisting of four industry leaders in the field of computers and optical storage technology - the 3M Co., IBM, Philips Netherlands and Philips North America (Tarrytown, NY) - are in a partnership to advance the state of the art of optical storage capacity. Under the Short Wavelength Optical Storage TRP, costs are split evenly among the government and participating partners. The purpose of the research is to develop a short-wavelength laser optical disk system using a blue-green laser diode. Such a system should produce about a 16-times increase in the storage capacity currently available on optical disks.
The program's goal is the ability to store 20 GB of data on a standard 5.25-in., dual-sided, rewritable optical disk. In addition to current military uses of 5.25-in. optical-disk systems, such as the F-16's and other large database requirements, the technology is expected to have extensive value to commercial users of optical storage such as insurance companies, banks and other financial enterprises and medical institutions.
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|Title Annotation:||Information Storage; includes related articles|
|Publication:||Journal of Electronic Defense|
|Date:||Feb 1, 1997|
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