Terence O’Kelly

Micro Hard Drives
From cave walls to stone tablets to papyrus tophotographic film to laser devices, storage technology
has always come up with new ways to hold and preserve
information. We often overlook the fact that sometimes older
methods coexist with the latest innovations simply because theolder methods have advantages that cannot be ignored. In the electronic age, paper is ingreater use than ever before in human history. For digital storage, magnetic recording—considered by many to be dying with tape—still leads the way in the greatest advances instorage capacity. The new Memorex Mega TravelDrive takes advantage of these latest
advances to offer capacities beyond flash drives in a more affordable package.
PIONEERS OF MAGNETIC RECORDING
Thomas Edison was the first to record sound, using wax cylinders and a recorderpatented in 1877. Oberlin Smith, a mechanical engineer from New Jersey, visited Edison
the following year and that same year proposed the first methods of magnetic recording
on undefined media. Valdemar Poulsen of Denmark actually produced a magnetic audio
recorder in 1893 using steel wire as the medium, and in 1934 German engineers began
making magnetic tape, the most commonly recognized form of magnetic media. Edison’s
wax cylinders waned in the face of Emil Berliner’s flat platters, the shape copied by vinyl
records, CDs, and DVDs. This platter shape was also used for magnetic media; but thesemedia were hidden from view in vinyl jackets (diskettes), plastic cases (micro diskettes),and sealed cases (hard drives and disk packs). Optical discs have now replaced
diskettes and tape in common use. In time they, too, will yield to new challengers fromthe future—holographic storage for optical storage, solid-state for electronic storage, andadvanced hard discs for magnetic storage using the same principles proposed by Oberlin
Smith.
PRINCIPLES OF MAGNETIC RECORDING
The basic principles behind magnetic recording are simple: all magnets have two poles-one with a positive charge and one with a negative charge. 1 The charges are best
defined when the poles are separated from each other as far as possible, as in a long, thinbar. When the “bar” is a microscopic crystal with a single magnetic domain, it isimpossible to eliminate or reduce the magnetic charge on the crystal. It is magnetic
forever. It is possible, however, to reverse the charge so that the negative pole of thecrystal becomes the positive pole and the positive pole becomes negative. A powerful
1

The ancient Greeks rubbed amber, fossilized sap, to put a static charge on it. Small rods ofstatically charged amber floating on water worked as magnets in early compasses. The Greek
word for amber is electrum, and the association between magnetism and static charges led to ourword “electricity.”magnetic field can force or coerce the poles to switch. The stronger the charge on thecrystal, the harder it is to coerce the change in polarity; and the measurement of thestrength required to switch the poles is the crystal’s “coercivity.” Oberlin Smith realized hecould draw magnetic patterns in material coated with millions of tiny magnetic particles by
arranging their poles under a coercive force. A magnetic “writer” creating varying
magnetic fields will leave a record of those variations in magnetic material pulled past thewriter, just as a moving pen writes on paper pulled under it in a lie detector. This remains
the basic design used today.
The writers are electromagnet heads that have a gap between their poles. As varying
amounts of current run through the head, a varying magnetic field spreads from the gap.
When blank magnetic tape is pulled across the head during recording, the billions of
microscopic magnetic particles that make up the pigment coating 2 magnetically rearrange
themselves to match the magnetic field above them as they pass below the gap in thehead (Figure 1). The particles do not move physically; they are frozen in position within
the coating. They merely rearrange the polarity of their magnetic poles to simulate thefield under the gap as they passed below as if the head were “magnetically

Magnetic “Printing”

Figure 1
printing” a pattern in the pigment. When recorded tape is pulled across the head, themagnetic pattern on the tape passing below the gap creates a small varying current in thehead that matches the original current that made the recording. The head now “reads” thepattern on the magnetic coating. The pattern can be rewritten by recording over thecoating again. Erasing the pattern is easy: the head creates magnetic fields that change
2The term “pigment” is used for tape-based media because the coating on the plastic film substrateacts as “magnetic paint.” Magnetic particles make up 40-50% of the coating thickness and the rest
is resins, dispersing agents, and other chemicals. Gamma ferric oxide crystals were the firstcommon magnetic particles, and they gave the tape a distinctive color. The same type of oxide isalso used as the pigment in inexpensive, stable paint used for barns and railroad boxcars. That’s
why both are often a brownish red.

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too fast for the particles to react uniformly. Half the particles in any area are magnetized
one way while the other half are magnetized the other way in a completely random way.
No pattern exists, and the coating is “blank.”
THE INTRODUCTION OF THE HARD DRIVE
Tape is an excellent magnetic medium for recording, but it has twoweaknesses: 1) it is a contact medium that must rub against themagnetic head for the transfer of the magnetic field to and from thehead, and 2) it is a longitudinal medium—it takes a much longer timeto access a spot on the tape. The first weakness results in both tapeand head wear over time. The second makes it difficult to retrieve
information quickly--it’s easier and faster to find a track on an LP
record than it is on a cassette. IBM engineers in the early 1950s
decided to combine the advantages of magnetic recording with theadvantages of the vinyl record. In 1956 they introduced the IBM 305
RAMAC (Random Access Method of Accounting and Control). It
stored a mere 4.4 megabytes of information—about the same dataamount as one song on an iPod--spread over 50 discs, each of which
was 2 feet (0.6 meters) in diameter.

RAMAC’s 50 platters

The innovative part of the design was that the head did not contact thediscs but sat in a robotic access arm that positioned itself just above the discs in order to avoid
touching them and to prolong the life of both discs and head. By 1962 IBM had designed heads
that literally flew over hard discs by riding a cushion of air according to Bernoulli’s Principle.
When a computer “crashed,” it usually described exactly what the magnetic head physically did.
Figure 2 shows relative sizes of the types of debris that can cause head crashes.

Figure 2
Design goals for magnetic recording have always included increasing the density ofmagnetic recording and shrinking the size of the media and the recorders. The huge discarrays and disc packs of the 1950s have given way to small, then mini, and now micro
hard drives that hold a thousand times more data in a form factor not much larger than acontrol button on the earliest drives. Thin glass platters have replaced aluminum platters
because the glass is more rigid than aluminum as the thickness decreases. The size,3speed, and materials have changed; but the principles behind even the most advanced
micro hard drives are those Oberlin Smith outlined over a hundred years ago.
MICRO DRIVES: TECHNOLOGY GOES TINY
Figure 3 is a picture of a micro hard drive. The aerodynamic electromagnetic head lies atthe end of a lightweight access arm that can position the head anywhere on the hard discplatter in thousands of a second. Instead of multiple 2-foot (0.6-meter) platters, the micro
hard drive discs measure a mere 0.85, 1, or 1.8 inches (38.8, 45.7, or 25.4 mm) indiameter. 3 The disc spins at speeds of 3,200 to 4,200 rpm; and in some large-capacity
versions of these tiny drives, there are two discs in each drive. A very thin coating ofcobalt/chromium/platinum alloy deposited on a thin glass platter gives the disc its
magnetic properties. The design of the micro drives is nearly identical to that of standard
hard drives used in all computers today except that all the parts are smaller and thespeeds are somewhat slower. These drives lack the IDE or SATA cable connectors of
their larger brothers because they are often designed to transfer data through otherinterfaces such as Compact Flash or USB connections. In many cases, the drives arepermanently embedded in a device and as in the Apple iPods. Figure 3 is an example ofsuch an embedded drive with its ribbon cable connector.

Hard disc platter

Figure 3

Flying head

Access arm

Although the design of micro hard drives is amazingly miniaturized, the concept ofmagnetic recording in the laser age seems rather crude. Laser light does not wear out themedium any more than flying heads would, and lasers are so much more “high-tech” thanmodifications to devices dating from the 1950s. The laws of physics, however, are
immune to fashion. The fact is that thousands of magnetic particles laid end to end can fit
in a wavelength of light—even blue laser light. That means there is much greater storage
density potential in magnetic materials than in optical discs.

3Common diameters of hard drives and their upper limits: 1-inch/12GB; 1.8-inch/60GB;
2.5-inch/160GB; and 3.5-inch/1TB.

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One problem has been that when these tiny particles, each of which is a single magnetic
domain, lie end to end, there is some cancellation of magnetic flux (energy) where positivepoles lie directly next to negative poles. That cancellation can lead to self-erasure whenthe magnetic material cannot sustain the smallest magnetic patterns that a record head iscapable of producing.
PERPENDICULAR RECORDING—AN OLD THEORY BECOMES REALITY
One solution to the problem of self-erasure has been to align the particles vertically in thecoating rather than end to end so that more magnetic domains can be packed in thecoating. Poles of opposite polarity attract each other, so positive poles next to negativepoles can reinforce each other. Since the morphology (shape) of the domain isperpendicular rather than horizontal, there is less self-erasure and sharper delineation of
the flux patterns that can be recorded on the vertical tips of the magnetic particles than on
their ends. See Figure 4.
This new arrangement of magnetic domains allows “perpendicular recording,” a goal ofmagnetic media manufacturers for some time because of the dramatic increase in flux
density allowed by magnetic domains standing head to toe instead of lying end to end.
Hard drive manufacturers are just now moving to perpendicular recording as a means toincrease storage capacity without increasing the size of the drives or media. Optical
recording will only see such a dramatic leap in density when it moves to holographic
recording instead of using single wavelengths of light in molded pits. 4

Greater Flux Density ofPerpendicular Recording

End to end distribution of single magnetic domains

Greater flux density with perpendicular alignment
Less self-erasure of magnetic domains
Figure 4

MAGNETIC RECORDING VERSUS SOLID STATE
There are factors other than recording density that determine which medium is best suited
for storage. Two of the most significant factors are cost and reliability. Cost is generally

4Critics of optical recording can liken today’s methods of using light patterns bounced off moldedpits as a “more advanced method of IBM’s old punch-card technology.”

5calculated as the cost per gigabyte of capacity. Magnetic media, including tape products,
generally have held a significant advantage simply because the storage density of suchmedia is so large per unit. Despite their complexity, micro hard drives maintain that
advantage over less complex devices such flash media. The costs of flash media
continue to decrease as memory chips become less expensive and production
yield rates improve; but with the leap in density provided by perpendicular recording,micro drives are likely to keep their cost advantage for the rest of the decade. Figure 5 isan estimate of costs per gigabyte of NAND flash compared to the estimates for the 1-inch
HDD (hard disc drive) for the next few years. The trend in more capacity at lower cost for
both media continues as it has for years.

1” HDD Cost Versus Flash
Twice the Capacity for the Same Cost
100

Cost ($/GB)

Flash cost projected to exceed
Moore’s law in the short term.
Sustainable?

10Flash Cost Estimate
1.0” HDD Cost

1” HDD maintains 2X$$/GB advantage through
2009

10.1
2003

2004

2005

2006

20072008

2009

2010

Mini HDD Cost per GB will continue to be ½ of that for Flash Memory

Figure 56

The real advantage flash media have over most other storage media is that they are solidstate—no moving parts. There are no alignment problems; no motors to act up; nobearings that need lubrication. Flash media fall and withstand shocks up to 2,000 Gs offorce without damage. Micro drives can actually withstand the same shock forces lasting
as long as 1 millisecond—as long as they are not operating. They are far more delicate
when spinning their discs: the shock rating drops to 200 Gs for a period of 2 milliseconds.
Some new designs actually incorporate “drop sensors” that stop a drive, park the head,and lock the head arm within 140 milliseconds (the amount of time it takes for anything tofall about four inches) so that the “operating shock” rating is very close to that of the “nonoperating shock.” Shock absorbent materials cushion tiny hard drives further to reducethe damage from impacts. The fact that the devices are so small and the parts have suchlow mass is part of the reason why they can sustain much more abuse than their bigger
brothers.
A surprise threat for hard drives comes from an unsuspected source. Because the headis actually flying over a cushion of air, it needs air to maintain its flight properly. Harddrives have small, well-filtered vents in them to balance internal air pressure with theoutside air pressure. At altitudes greater than 10,000 feet or 200 feet below sea level in
unpressurized environments there is insufficient air pressure to maintain the head’s proper
flight characteristics. These are unusual circumstances for most people, but they do posea real threat to hard drives used in harsh environments.
WHAT’S NEXT FOR MICRO DRIVES
What were once electronic “gadgets” have fast become essential parts of modern lives.
Cell phones are becoming digital cameras, audio and video players, GPS devices, andeven TV sets. Video and photo storage is now commonplace in the most popular MP3
audio players. These changes in portable devices and demands for even better quality
photos and high definition video in advanced cameras require more storage capacity thanever before—capacity that must remain small, light, and portable for “digital on the go.”
These requirements are precisely the greatest strength of micro drives—lowest cost pergigabyte. New developments will make the drives even thinner than today’s whileboosting capacity to 15GB—3,500 times greater capacity than the enormous IBM RAMAC
disc array! Micro drives are the best solution to satisfy consumers’ inexorable desire forgreater functionality and better quality at reasonable cost.
CONCLUSION
There is no perfect storage medium yet. Stone lasts a long time, but it is heavy andexpensive with very limited capacity. The same could be said for paper—one DVD canhold as much as eight file cabinets full of paper. Flash memory is the latest advance instorage, but it is still expensive. Magnetic recording remains the biggest bang for thebuck, and perpendicular recording breathes new life into its inherent advantages. Regular
hard drives, though, are fragile; and tape is a contact medium that wears over use. Micro
hard drives, including the new Memorex Mega TravelDrive, use a sophisticatedcombination of methods to increase their durability to nearly that of flash memory and still
maintain a cost advantage for the near future. They are 125-year old technology wrappedin a 50-year old format with the latest innovations—and they are here to stay.

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Laptops and computers currently use the magneto-resistance effect to read hard-disk data.
Hard disks store bits magnetically; depending on the direction of a bit's magnetic field, it
can represent a bit 1 or 0. As the read head flies over the disk, the magnetic fields of thebits cause a corresponding resistance change in the read head's sensor. The resistance can't
be measured directly, so it's first converted into a voltage using a direct current. (Thevoltage is equal to the current multiplied by the resistance.) In order for the whole thing towork, a current must run continuously through the sensor.
The new sensor will not need this constant current because it uses the magneto-electric8