A random access system is proposed for digital storage and retrieval of up to a Petabyte of user data. The system is comprised of stacked memory modules using laser heads writing to an optical medium, in a new shirt-pocket-sized optical storage device called the Opticel. The Opticel described is a completely sealed 'black box' in which an optical medium is accelerated and driven at very high rates to accommodate the desired transfer rates, yet in such a manner that wear is virtually eliminated. It essentially emulates a disk, but with storage area up to several orders of magnitude higher. Access time to the first bit can range from a few milliseconds to a fraction of a second, with time to the last bit within a fraction of a second to a few seconds. The actual times are dependent on the capacity of each Opticel, which ranges from 72 Gigabytes to 1.25 Terabytes. Data transfer rate is limited strictly by the head and electronics, and is 15 Megabits per second in the first version. Independent parallel write/read access to each Opticel is provided using dedicated drives and heads. A Petabyte based on the present Opticel and drive design would occupy 120 cubic feet on a footprint of 45 square feet; with further development, it could occupy as little as 9 cubic feet

Newell, Chester W.

English

NASA Technical Reports Server

"" "'"ii'-i'
N95- 24119
Petabyte Mass Memory System Using
the Newell Opticel*
Chester W. Newell
Primelink Technologies Inc.
#208, Advanced Technology Centre
9650 - 20 Avenue
Edmonton, Alberta, Canada T6N 1G1
Phone: + 1-403-440-0111; FAX: + 1-403-440-0110
Email: evergreen @maugham. ate.edmonton, ab. ca
S/i-Do
p-
Abstract
A random access system is proposed for digital storage and retrieval of up to a Petabyte
of user data. The system is comprised of stacked memory modules using laser heads
writing to an optical medium, in a new shirt-pocket-sized optical storage device called the
Opticel °. The Opticel described is a completely sealed "black box" in which an optical
medium is accelerated and driven at very high rates to accommodate the desired transfer
rates, yet in such a manner that wear is virtually eliminated. It essentially emulates a
disk, but with storage area up to several orders of magnitude higher.
Access time to the first bit can range from a few milliseconds to a fraction of a second,
with time to the last bit within a fraction of a second to a few seconds. The actual times
are dependent on the capacity of each Opticel, which ranges from 72 Gigabytes to 1.35
Terabytes. Data transfer rate is limited strictly by the head and electronics, and is 15
Megabits per second in the first version.
Independent parallel write/read access to each Opticel is provided using dedicated drives
and heads. A Petabyte based on the present Opticel and drive design would occupy 120
cubic feet on a footprint of 45 square feet; with further development, it could occupy as
little as 9 cubic feet.
Introduction
The Compact Disc digital audio player dramatically illustrated the classic criteria for a
successful new market entry: it produced a significantly higher-quality product in a
smaller size, with important new features yet at a competitive price, in a marketplace
which had stagnated.
The Newell Opticel promises the equivalent for video bandwidths: a digital recorder-
player module which, by meeting the same criteria, would bring about an even more far-
reaching revolution in the computer and home-entertainment markets.
Trademark
123
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The Opticel drive combines novel cartridge concepts with three other discrete
components: optical heads, optical media, and signal and control electronics. It is
packaged in a standard 3-1/2-inch form factor, one-half the volume of the highest density
5-1/4-inch CD ROM drive, with over ten times its capacity, yet with access times
comparable to single-disk systems, and transfer rates limited only by the digital
electronics.
There are many development efforts under way seeking such an objective. Those known
all suffer critical shortcomings: disk-based systems are bulky and have limited transfer
rates; tape-based systems have poor access times. The Opticel retains the advantages of
both with none of the fundamental disadvantages.
The Optical Head
Primelink is developing two heads:
(a) An IR-laser head, on a conventional 2-axis fine actuator movement (tracking and
focus) and a stepper-motor/ball-screw carriage assembly for coarse tracking, is
being designed.
(b) A red-laser-based, integrated, solid-state, multi-channel head system is being
researched, with no tracking movements (i.e. no moving parts).
The first head will go to production in mid-1995; the second is scheduled for release in a
second-generation product (probably around the year 2000).
The Optical Recording Media
Primelink has working agreements with two U.S. companies for archival or WORM
optical tape, and for non-archival, erasable tape. Both are compatible with the optical
head lasers.
The Data Encoding/Decoding Method
Background - The encode/decode technique normally used in today's WORM disks is to
ablate a pit using an IR laser. The data are encoded by phase-modulating the position of
the pit-edge along the track.
If the wavelength of the laser is _,, the numerical aperture of the lens N, and ablation is set
to occur at the 50% level on the Gaussian energy curve, then the pit diameter becomes
dpit = 2"--ff (1)
9412-16 124
A commerciallyavailablehead1 employs,for example,_, = 785 nm, NA = .53. This
gives a spot sizeof 0.74 micron. To allow for inter-trackgroovesand tracking servo
error,a trackpitchof 1.6micronis employed.Thisyieldsa rawarealdensityof
106
Draw = 0.74 x 1.6
= 0.84 x 106 cells/mm 2 (2)
A 5-1/4-inch CD-ROM provides 8 x 10 3 square millimeters of usable recording area. The
capacity of the ROM is thus
Cra w = 0.84 x 8 x 10 9
= 6.72x 10 9 cells (3)
For digital data, run-length-limited (RLL) encoding can be used, giving 1.5 bits/cell.
Formatting and error correction to a bit-error rate (BER) of a 1 x 10 -15 requires an
overhead of about 50%. The number of bits/cell is thus
N = 1.5x0.5
= 0.75 bits/cell (4)
The net user capacity is thus
C u_d_r
6.72 x 10 9 x0.75
8X10 6
= 630 MB (5)
High Densit3, Encoding
Two state-of-the-art techniques have been evaluated for the encoding/decoding circuitry:
(a) Light Intensity Modulation (LIM) - Asahi 2 has demonstrated that it is feasible to
reduce the spot diameter by as much as one-sixth that previously realizable for an
IR laser, and the track pitch to 0.87 micron, thus theoretically increasing the raw
storage capacity of a 5-1/4-inch CD-ROM to as much as 10 Gigabytes. This was
accomplished by modulating the light intensity of the laser, using feedback to
allow operation higher up on the Gaussian curve. To achieve this density in
9412-16 125
practice, however, would require a shorter-wavelengthreading laser and
extremelyhigh mechanicaltolerances.
Solid-stateblue lasersareunderdevelopmentby severalcompanies;3 however,
they arenot expectedto becommerciallyavailablefor severalyears. However,
greenlasersarebecomingavailableandshouldbe ableto resolvecell lengthsin
theorderof 0.47micron. This is alsomorepracticalmechanically.
Assuminga greenlaser,and assumingthe bits/cell of equation(4), the userbit
lengthusingLIM wouldbe:
0.47
d LIM
0.75
= 0.63 g (6)
Using Asahi's track spacing of 0.87 microns, this would give an areal density of
1
D-
.63 x 0.87
= 1.8 Mb/mm 2 (7)
(b) Mark Edge Recording - SOCS Research 4, Los Gatos, California, and Sony 5 have
demonstrated the ability to write three bits on both the leading and trailing edges
of the cell (see Fig. 1). Primelink has taken a license under this patent. Using an
IR laser, Primelink has demonstrated:
a track width of 0.87 microns
a cell with 6 bits on 1.67-micron centers gives an average bit length of
1.67
Dry, -
6
= 0.28 t (8)
Using the Sample Servo method for tracking in place of grooves, a track pitch of
1.2 microns was achieved. This gives a raw areal density of
10 6
Draw _"
0.28 x 1.2
= 3.0 Mb/mm 2 (9)
9412-16 126
The Cartridge/Drive System
As described above, the raw areal densities achievable using production heads and state-
of-the-art encoding techniques on 5-1/4-inch disks, have been demonstrated to be
between 1.5 to 3.0 Megabits per square millimeter.
Primelink has developed a digital video optical recorder using the Mark Edge Encoding
method on phase change (reversible) and ablative (archival) media. To provide "high
fidelity" video graphics to the PC market, it was assumed that at least VGA resolutions of
640 x 512 pixels/frame are needed. To upgrade NTSC and VGA to SVGA resolution and
provide for HDTV quality for ultimate home entertainment systems, two proprietary
DSP algorithms were used to quadruple the pixels to 1280 x 1024. 8 bits/pel were used
for luminance, 4 bits/pel for each of the chrominance pixels. From subjective tests using
a simple, proprietary, lossy compression algorithm, it was determined that compression
ratios of 10:1 would yield decompressed images subjectively virtually indistinguishable
from the original.
Using the above parameters, the required user capacity/frame during transmission and
storage is
Cu_e_! frame =
640x512(8 + 4 + 4)
10
= 0.52 Mb/frame (10)
For full motion, 30 frames/sec, are required. The average bit transfer rate is thus:
BTR = 0.52x 10 6 x30
= 15.7 Mb/s (11)
C_=/hr. =
15.7 x 106 x 3600
8 X 10 9
= 7.1 GB/hr. (12)
Combining equations (7), (8), and (12), and allowing 50% overhead for error correction
and formatting, the recording surface area required, depending on the laser/media
required, is:
A/hr. =
7.1 x 109 x 8
(3.0 to 1.8) x 106 X 0,5
= (3.8to6.3) X 104 mm2/hr. (13)
9412-16 127
Background
Using 5-1/4-inch CD-ROM disks with a useful area of 1 x 10 4 square millimeters, from
equation (13), the number of disks required would be:
N = 3.8 to 6.3 disks/hr. (14)
This is not an attractive solution for digital video, for the following reasons:
l° To be a next-generation (full bandwidth digital) version of SVHS (analog)
recorders, the capacity should provide for at least 5 hours. 20 and 40 CD-ROM
disks or two disks, requiring a stackloader, 15 to 20 inches in diameter would be
needed.
. Even the 5-1/4-inch drive form factor is too large for lap-top computers and hand-
held camcorders. A single standard for universal application would not be
possible. This is a requirement for the Primelink system.
For 15.7 megabits per second transfer rate, 50% overhead, from equations (6) and (8), the
required beam writing velocity is:
V = 15.7 (0.28 to 0.63) x 2
= 10 to 20 m/s (15)
and the total capacity required is:
C_, = 7.1 x5 = 35.5GB (use36GB) (16)
While this writing velocity is not difficult to achieve with rotating disks and stepped
laser-optical heads, disks have been shown above to be impractical for our purposes
because of their limited capacity. To achieve the required storage area, especially in a 3-
l/2-inch form factor, a tape system became mandatory.
Known attempts to achieve such optical beam writing velocities using conventional tape
drives have all employed scanning devices of one type or another:
(1) Rotating scanners:
Many historical attempts have been made using rotating prisms, lasers on head-
wheels, etc. They have invariably failed to reach the market in small, modest-cost
systems because of the problem of tracking to the tolerances of laser writing.
9412-16 128
(2) Solid-statescanners
LaserTapeand others have attempteduse of solid-state scannerswithout
commercialsuccess,becauseof difficulty in achievingthe requiredscananglein
compact-geometrysystems,aswell asin trackinglateraltapeskew.
(3) Linear-motorscanners
CREO is the only companywhich hasachievedsubstantialsaleswith an optical
taperecorder. Using a linearmotor-drivenplatform on which 16writing and 32
readinglasersare arrayed,a stationaryfield of 35-mm. tape is scanned,after
which the tape is incrementedto the next field. The systemis mechanically
massive,and sellsfor about$250,000CDN. This approachofferedno solution
for thePrimelinkproject.
The Newell II (NII*) Tape Cartridge 6 can easily achieve the required writing velocities
without use of an intermediate scanner, and could have been used for this application.
The author demonstrated such a cartridge at Newell Research Corp., using 100 meters of
8-millimeter ICI optical tape on 25-micron basefilm, thus providing 8 x l0 s square
millimeters of surface area at tape speeds to 1000 inches per second. This would
potentially provide raw capacities of
CNIt
(1.8 to 3) x 106 x 8 x l05
8
= 180 to 300 GB (17)
for video recording times of
180 to 300
T =
7.1
= 25 to 42 hours (18)
Such a system was an "overkill" for the proposed Primelink project, however, and would
be more expensive than desired because the cartridge must be reversed at beginning and
end of tape. The pulse-power of the motor-drive system required to reverse the system
within a time interval that could be economically buffered for continuous video, would be
high.
"Trademark
9412-16 129
The Newell Opticel 7
The low tape consumption required for the Primelink project suggested the use of an
endless tape loop in a "scramble bin." Such a loop in concept is much simpler than the
NII cartridge, in that no tape drive belts or tape reels are required within the cartridge (see
Figs. 2,3).
While endless loop systems are well known in magnetic tape systems, the unique
problems of an optical tape system using a loop were not trivial, due to the following
factors:
* The loop must revolve at high speeds, thousands of times during each record/play
cycle.
• The optical recording surface must not be fogged during the life of the cartridge
(hundreds of thousands of passes).
• Due to the sub-micron dimensions of the bit cell, debris must not be allowed to
accumulate on recorded surfaces from wear or environmental contamination.
• The film must be coupled to the drive and tensioned precisely in the longitudinal
direction (X-axis control).
• The film must be edge-guided with very low edge pressure to avoid edge fatigue (Y-
axis control).
• The film must be stable in the axis of the laser optics due to very shallow focal depth
of the optics (Z-axis control).
Each of these problems, and the method for dealing with it, is disclosed in several patents
pending, available on request under a suitable Confidential Disclosure Agreement.
To achieve five hours of high-definition digital video, 16-millimeter tape was used, and
two loop lengths were provided for the two encoding methods:
L = 5(3.8 to 6.3) x 10 -2
16 x 10 .3
= 12 to 20 m (19)
To achieve long life, bending stresses in the tape were kept within 35% of elastic limits,
and no optical surfaces or tape edges touched any other surface. The Opticel case was
hermetically sealed and back-filled with one atmosphere of a suitable dry gas. 12.5-
micron tape was used.
9412-16 130
TheaboveparametersrequiredOpticelcasesizesof:
Height: 18.5mm
Width: 90mm
Length: 95mm and 140mm
ThestandardOpticel is on thefootprint of a 3-l/3-inch floppy disk.
Thedrive usedexactlythesameelementsasaWORM diskdrive:
• Laser head (with Y-Z axis control)
• Drive motor (brushless)
• Control and DSP electronics (ASICs)
3-1/2-inch standard drive dimensions were employed:
Height: 41.3 mm
Width: 101.6 mm
Length: 152.4 mm
An Interchanzeable Opticel Usinz the Nil Principle
To achieve much higher capacities, the same cartridge/drive interface geometry of the
Opticel scramble-bin cartridge can be employed in an NII-type cartridge (see Fig. 3).
This allows a high-performance drive system to be developed that would be downward
compatible in writing and reading the Opticel.
The NII development is not within the scope of the present Primelink project. However,
this development would be a logical follow-on to the Newell Opticel.
Summary
• The Opticel drive uses the 3-1/2-inch standard form factor for both standard and
"stretch Opticels.
• The time to the first bit is less than 5 milliseconds; to the last bit is 1 second for the
standard Opticel, 2 seconds for the "stretch" Opticel
• The parts count in the drive is lower than that in a typical 5-1/4-inch WORM optical
disk drive.
• Capacity of each Opticel (formatted data with BER of 1 x 10 -'5) is 36 Gigabytes for
the standard Opticel, and 72 Gigabytes for the "stretch" Opticel.
9412-16 131
Two Proposed Petabyte Systems
Based on the loop Opticel
A "stretch" Opticel with MER encoding using 24 meters of tape gives 72 Gigabytes per
Opticel. This will fit in a &inch drive, with 1-1/2-inch overhang.
For a Petabyte, number of drive modules needed is:
10 Is
= 13,889
72 x 109
In a stack loader (see Fig. 4) use:
64 modules/column
8 columns/drawer
3 drawers/cabinet
9 cabinets
This would give dimensions of:
Height: 2.75 m
Depth: 0.813 m
Width: 0.572 m x 9 = 5.15 m
With additional R & D the size and access time can be reduced by using:
• Smaller cells:
Light intensity modulation, MER encoding
Short wavelength laser (green or blue)
Tighter track servoing
From Asahi predictions:
Minimum cell size: 0.2 I,t
0.20
Cell spacing: 1.67 x - 0.45t, t
0.74
Track pitch: 0.871,t
9412-16 132
Equation (9) becomes:
D •
raw
6 x l0 s
0.45 x 0.87
= 15 Mb/mm 2 (9")
Thinner tape:
The limiting factor is the shear strength between coating and basefilm; ie., the
capacity is inversely proportional to the basefilm thickness. By using 4-
micron basefilm, maximum length in the "stretch" version can be increased,
and equation (19) becomes
12.5
L = 24x_
4
= 75 m. (19')
Higher tape velocity:
Primelink has attained tape velocities of 25 meters per
difficulty, giving an access time of 3 seconds to 75 meters.
second with no
User capacity/Opticel with loop would thus increase to:
C u sel"
0.5 x75 x 15x 16x 10 9
= 1.125 TB
For the Petabyte, number of drive modules would be:
(20)
103
- 889
1.25
The stack loader would require only two drawers in one cabinet.
Based on the NII Opticel
The NII cartridge with 4 micron tape can store 450 meters of 16-millimeter tape in the
standard Opticel case size.
• Again, using proven MER encoding with IR lasers, the user capacity becomes
9412-16 133
0.5 x 450 x 3 x 16 x 10 9
C uselr
- 1.35 TB
Maximum access time would be 18 seconds.
would be
(21)
Number of drive modules for a Petabyte
103
= 741
1.35
Again, two drawers in one cabinet would be required.
Using LIM encoding with green lasers, the user capacity could be theoretically
increased fivefold to 6.75 Terabytes, reducing the number of modules to 148, thus
reducing cabinet dimensions to, say
Height: 1.60 m
Depth: 0.813 m
Width: 0.470 m
Its volume would thus be 9 cubic feet.
REFERENCES
,
2.
t
.
,
o
7.
Mitsubishi ME3H 1.
I. Morimoto et al., "Ultrahigh Density Recording Using Overwritable Phase
Change Optical Disk," SPIE Proceedings, Feb., 1992.
W.J. Kozlovsky et al., "Optical Recording in the Blue Using a Frequency-
Doubled Diode Laser," SPIE Proceedings, Feb. 1992.
U.S. Patent No. 4,736,258, "High Density Storage of Information on a Compact
Disc."
S. Kobayashi, J. P. de Kock, T. Harigome, H. Yamatsu, H. Ooki, "High Density
Optical Disk Recording by Pit Edge Modulation," Corporate Research
Laboratories, Sony Corporation.
U.S. Patent No. 4,172,569, "Tape Transport System With Peripheral Belt Drive."
U.S. Patent Pending, Primelink Technologies Inc.
9412-16 134
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136


Petabyte mass memory system using the Newell Opticel(TM)

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