WM. 3 No. a
`.
`$2.85 in USA
`'
`1.: al£2.1D In 0.K.
`Puhllcntlon
`
`MASS STORAGE
`
`Apple Exhibit 4208
`Apple v. SightSound Technologies
`CBM2013-00020
`
`Page 00001
`
`Apple Exhibit 4208
`Apple v. SightSound Technologies
`CBM2013-00020
`Page 00001
`
`

`

`Managing Editor
`Mark Haas
`Technical Editors
`Gregg Williams. Senior Editor;
`RichardS. Shuford. Curtis P. Feigel.
`Arthur Little. Stanley Wszola.
`Pamela Clark. Richard Malloy;
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`Ciarcia, Mark Dahmke. Consulting Editors;
`Jon Swanson. Drafting Editor
`Copy Editors
`Beverly Cronin. Chief;
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`Assistants
`Faith Kluntz. Beverly Jackson. Lisa Jo Steiner
`
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`Advertising
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`Marketing Communications
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`Michele P. Verville. Research Manager
`
`Controller's Office
`Kenneth A. King. Asst. Controller;
`Mary E. Fluhr. Acct. & DIP Mgr.; Karen
`Burgess. Jeanne Cilley. Linda Fluhr. Vicki
`Bennett. L. Bradley Browne. Vern Rockwell
`Business Manager
`Daniel Rodrigues
`Traffic
`N . Scott Gagnon. Manager;
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`Receptionist
`Jearyann Waters
`Publishers
`Virginia Londoner. Gordon R. Williamson;
`John E. Hayes. Associate Publisher;
`Cheryl A. Hurd. Publisher's Assistant
`
`Officers of McGraw-Hill Publications Com(cid:173)
`pany: Paul F. McPherson. President; Executive
`Vice President: Gene W. Simpson; Senior Vice
`President-Editorial : Ralph R. Schulz; Vice
`Presidents: Kemp Anderson. Business Systems
`Development; Shel F. Asen. Manufacturing;
`Harry .L. Brown. Special Markets; James E.
`Hackett. Contrqller; Eric B. Herr. Planning and
`Development H. John Sweger. Jr .. Marketing.
`Officers of the Corporation: Harold W.
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`Officer; Joseph L. Dionne. President and Chief
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`Treasurer.
`
`4 March 1983 © BYTE Publications Inc
`
`In This Issue
`
`Sophisticated new operating systems and multitasking software promise
`alter significantly the way we use personal computers. Because of the
`memory requirements of the new software, we're sure to see changes for
`better in the nature of external storage devices. New technologies for
`storage will become even more critical as the software revolution continues
`escalate. As Robert Tinney's cover suggests, personal computers will
`large quantity of high-speed mass storage to hold all the software and
`data that we'll generate. Our theme articles address the latest de'"~II:Jorn~r1tt~
`in mass storage. Clark E. Johnson Jr. discusses "The Promise of p.,,.n .. nr1lir•
`Magnetic Recording.'' Tom Moran looks at "New Developments in
`Disks;· Edward Rothchild writes about "Optical-Memory Media,"
`Sarisky explores the question "Will Removable Hard Disks Replace the
`py?" Jim Toreson concentrates on "The Winchester Odyssey," and in
`of a three-part series Andrew C. Cruce and Scott A. Alexander
`"Building a Hard-Disk Interface for an S-100 Bus System." Plus we have
`of "NAPLPS, A New Standard for Text and Graphics," the second in~t~lll rrJt ... nt
`in the VIC-20 series, "Adding a 3K-Byte Memory Board," a review of
`from Digital Research, and BYTE's Game Grid. Steve Ciarcia tells you
`"Build the ECM-103, an Originate/Answer Modem.'' and more.
`
`BYTE is published monthly by McGraw-Hill. Inc.. with offices at 70 Main St. Peterborough
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`•h<·rriootirm<
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`for lost manuscripts or
`copyright © 1983
`photos. Opinions expressed by the authors are not necessarily those
`the copyright owner for
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`base fee of 5 I .00 per copy of the article or item plus 25 cents per page.
`should be sent directly to the
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`bulk orders should be addressed to
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`Page 00002
`
`

`

`"II
`Volume 8, Number 3
`Features
`26 Build the ECM-103, an Originate/Answer
`Modem by Steve G:iarcia I The Texas Instruments
`TMS99532 forms the heart of a Bel!- I 03-compatible
`modem.
`34 The Enhanced VIC-20, Part 2: Adding a
`3K-Byte Memory Board by Joel Swank I Supplement the
`VIC-20's standard SK bytes of RAM and eliminate those
`annoying "out-of-memory" messages.
`44 A User's VIew of COMDEX by Jerry Pournelle I ·
`impressionistic report of one of the largest gatherings of
`dealers and manufacturers.
`6 The Promise of Perpendicular Magnetic
`by Clark E. Johnson Jr. I As the Japanese
`to have realized already, PMR represents the next
`of recording technology.
`68 New Developments In Floppy Disks by Tom
`n I New advances in floppy-disk-drive technology
`rs intense competition.
`86 Optical-Memory Media by Edward Rothchild I
`background on how optical disks work, who makes
`and how much data they can hold.
`1 0 Will Removable Hard Disks Replace the
`Larry Sarisky I Improved data-storage
`•dr·nn,()rr'n"'< may eventually eliminate floppy disks.
`1 2 2 The Winchester Odyssey, From Manufacturer
`User by Jim Toreson I A look at drives, OEMs, and the
`of doing business.
`·
`Building a Hard-Disk Interface for an S-100
`System, Part 1 : Introduction by Andrew C. Cruce
`Scott A. Alexander I The first in a series of articles on
`;~ .... ,.~•nn"' a Winchester disk drive to an S- I 00 bus CP/M
`
`User's Column: Sage In Bloom, Zeke II, CBIOS
`L .. , •• u,, .. L,., Debate Continues by Jerry Pournelle I
`computer user tackles his new writing
`
`Faster Binary Search by Dr. L. E. Larson I An
`ue results in faster-running applications
`shorter response times.
`Collection with a Microcomputer by Dr.
`I Using a TRS-80 Model I for environ(cid:173)
`time and money.
`Memory, Part 1: How to Construct
`M.,,m,.,rv with 4116 Memory Devices by
`advantage of the low price of the
`
`March 1983
`
`3 _Jt1 A Peek Into the IBM PC by Tim Field I An
`assembly-language program enables an Epson printer to
`display all 256 characters used by the IBM PC.
`389 Keywords In a Fuzzy Context by Thomas A.
`Smith I CBASIC programs for bibliographic search tell you
`the degree to which various articles meet your
`requirements.
`418 ROTERP: An Interpretive Language for Robot
`Control by Gary Liming I High-level languages may help
`bridge the gap between artificial intelligence and the home
`experimenter's robot.
`436 Using SOUND Arguments for High-Precision
`RTTY by Scott Persson I How to generate radioteletype
`audio frequencies from an Atari 800.
`453 Binary-Format Number Storage on the Apple II
`Disk by David Eyes I A machine-language routine to read
`and write binary data to a text file .
`
`Reviews
`190 MP/M II by Stephen Schmitt
`247, 248, 251 BYTE Game Grid: Project Nebula by
`Keith Carlson; Legionnaire by Gregg Williams; Omega
`Race for the VIC-20 by Stanley J . Wszola
`2 56 Ouickcode by Adam B. Green
`282 Hayes's Stack Smartmodem by Norman C. McEntire
`
`Nucleus
`
`6 Editorial: The Software Revolution: Where Will We
`·Store All Those Programs?
`14 Letters
`22 BYTE's Bugs
`307, 450 Programming Quickies: Add Dimensions to Your
`BASIC; Computing Telescope Parameters with the
`OSI Superboard II
`380, 462 System Notes: Circles and Ellipses on the Apple
`II; Adding a Trace to North Star BASIC
`474 EventOueue
`478, 486 BYTE's Bits
`484 Software Received
`487 Ask BYTE
`490 Books Received
`491 Clubs and Newsletters
`492 BYTELINES
`497 What's New?
`557 Unclassified Ads
`558 BOMB, BOMB Results
`559 Reader Service
`
`Page I 52
`
`Page 247
`
`Page 00003
`
`

`

`Will Removable Hard Disks
`Replace the Floppy?
`Improved data-storage technologies may eventually
`eliminate floppy disks.
`
`Larry Sarisky
`Syquest Technology
`47923 Warm Springs Blvd.
`Fremont, CA 94539
`
`The floppy-disk drive has been the
`method of choice for data storage for
`several years now. But like all de
`facto standards, its dominance is be(cid:173)
`ing challenged, in this case by the
`development of a new storage
`medium-the removable hard-disk
`cartridge.
`The cartridge appears to offer all
`the advantages of the floppy disk as
`well as increased storage capacity and
`access speed. But before describing
`this new method of data storage, let's
`take a look at how and why floppy
`disks were developed;
`the
`When
`IBM
`introduced
`System/360 computers,
`their low(cid:173)
`level microcode programs were
`
`About the Author
`Larry Sarisky is the vice-president of sales and
`marketing for Syquest Technology. He has
`more than 12 years' experience in marketing
`data-storage products.
`
`110 March 1983 © BYTE Publications Inc
`
`stored in read-only memory (ROM).
`By
`the
`time
`the IBM 370 was
`developed, however, semiconductor
`technology had advanced so far that
`microcode storage could be
`im(cid:173)
`plemented
`in . semiconductor
`.memory. This memory was volatile,
`
`Newer microprocessors
`can make use of
`virtual storage only
`with the faster access
`speeds offered by hard
`disks.
`
`so a · microcode loading-and-storage
`device was necessary. Magnetic tape
`was considered, but the need for
`loading diagnostic programs as well
`as microcode presented a problem. So
`in 1973, IBM developed a cheap disk
`
`and drive that provided the random(cid:173)
`access speed needed for diagnostic(cid:173)
`program loading. This low-cost, flex(cid:173)
`ible disk gave IBM an economical
`random-access program-loa
`device. And once such a device
`available, it was easy to add a wriit .. ·t•
`capability for data storage. :::ie1mcon-1
`ductor technology and the IBM
`had set the stage for the floppy
`the data-storage medium that
`launch the small-computer
`tion.
`revolution, however,
`The
`spearheaded not by IBM but by in•
`dependent manufacturers of floppy
`· disks such as Shugart Associates and
`Memorex, who saw the value of low·
`cost,
`random-access . storage for
`smaller computers; By 1975, 27 in•
`dependent suppliers were
`8-inch floppy~disk drives.
`The new medium
`.for
`offered potent advantages.
`
`Page 00004
`
`

`

`The Winchester Disk
`. While. lower-cost 5 1/4-inch floppy
`disks gamed most of the attention in
`1976, Memorex saw another IBM.
`developed storage technology that
`could be used in small computers. Its
`Model 601 hard disk was the first
`. small Winchester system
`to be
`_ ~.:"available from a source other than
`IBM. By protecting the read/write
`heads and disk platters in a sealed en(cid:173)
`vironment,
`the Winchester could
`deliver higher data-storage capacities
`faster access, and greater reliability a~
`a lower cost per byte. While the 601's
`disk diameter was a hefty 14 inches
`successive Winchester-technolog;
`disk drives redu~:ed it to 8 inches and
`then 5%. inches.
`The history of disk storage has
`been a tale of increasins compactness.
`The first 14-inch Winchester-type
`drives paralleled established storage(cid:173)
`module devices. The 8-inch Win(cid:173)
`chester followed the 8-inch floppy
`disk. The 5%-inch drive was com(cid:173)
`patible in size with its corresponding
`
`Photo 1: A size comparison of the 3.9-inch removable hard-disk cartridge drive with
`standard 5¥4 - and 8-inch floppy-disk drives. The cartridge drive is 1.625 by 4.8 by 8
`inches.
`
`Business Week reported in a May 17,
`1976, article, "Each standard disk
`(floppy) has the data-storage capacity
`of 3000 punched cards. The disks are
`also reusable, easier to store and
`mail, and inexpensive." The article
`also predicted that "a new market
`segment is opening up thanks to the
`development of the cheapest of com(cid:173)
`puters-the microprocessor or com(cid:173)
`puter-on-a-chip."
`As
`these prophetic words were
`
`written, Shugart Associates was
`developing a
`lower-cost 5:Y4-inch
`flexible-disk drive . It was this drive
`that signaled the decline of cassette
`·tape. The 5%-inch floppy-disk drives
`and media cost less than comparable
`cassette-based .storage. They offered
`an average access time of about half a
`second compared to the cassette's 20
`seconds. And their error rate was two
`orders of magnitude better than that
`of cassettes.
`
`Page 00005
`
`

`

`the
`finally,
`flopPY disk. And,
`(see
`3.9-inch hard-disk cartridge
`hoto 1) parallels
`the newer
`p
`fl
`.
`"
`"micro opp1es .
`
`The Need for Better Disks
`The development of 16-bit pro(cid:173)
`cessors, more complex operating
`systems, and multiuser, multitasking
`configurations has increased the need
`for hard-disk capacity, reliability,
`and speed. Newer processors can
`make use of virtual storage only with(cid:173)
`the faster access speeds of hard disks.
`Operating systems such as Unix
`have a large assortment of utilities
`that won't fit on a floppy . To perform
`multiple
`tasks for multiple users,
`systems required the capacity and ac(cid:173)
`cess speed available only from hard
`disks.
`Microcomputer applications are
`becoming far more sophisticated. A
`business accounting system can re(cid:173)
`quire a box of 10 floppy disks. A
`high-resolution digitizing camera
`may need more than a megabyte of
`data storage for a single picture.
`
`Database-management systems, com(cid:173)
`puter graphics, English-language(cid:173)
`based programming, extensive menus,
`and broad-based application packages
`all require faster access to a larger
`amount of data than a single floppy
`disk can hold .
`
`If a fixed disk crashes,
`it can be replaced only
`by a factory technician.
`
`The Limitations of Fixed Disks
`While fixed-disk Winchester drives
`are suitable for many applications,
`they present severe integration prob(cid:173)
`lems for smaller computer systems
`that now use one or two 5%-inch
`floppy-disk drives. The 14-inch drive
`is simply too big and too heavy to be
`integrated
`into many existing
`systems. It also requires a more
`sophisticated interface and both AC
`and DC power-supply voltages.
`The smaller 5%- and 8-inch Win-
`
`chester drives have proved to be more
`practical for small systems, but they
`are no panacea. Although they're
`smaller than the 14-inch drives, they
`still may be
`too large for some
`systems. Why? Because most ~ystems
`have required both removable and
`fixed media. If the current system has
`been designed for one or two 5%-inch
`floppy disks, there may not be room
`to add a fixed-disk drive.
`The user must also worry about the
`possibility of a fixed-disk failure . If
`the fixed disk crashes,
`it can be
`replaced only by a trained technician.
`Even worse, data may be lost forever.
`For this reason, most users back up
`important programs and files on flop(cid:173)
`py disks or tape. Unfortunately, the
`floppy disk is often inadequate for
`backup. Small Winchester drives
`have capacities that range from 5 to
`80 megabytes. Backing up that much
`storage on floppy disks is inconve(cid:173)
`nient and slow. And although tape
`can be used for backup, it lacks the
`random access, reliability, and ser(cid:173)
`viceability of disk storage.
`
`W.A. Brown Instruments, Inc.
`Fort Lauderdale, Fl
`(305) 776-4800
`W.A. Brown Instruments, Inc.
`Melbourne, FL
`(305) 723-0766
`W.A. Brown Instruments, Inc.
`Tampa, FL
`(813) 985-0394
`Cain I Bultman, Inc.
`Jacksonville, FL
`(904) 356-4812
`Halt·Mark Electronics Corp.
`Fort Lauderdale, FL
`(305) 971-9280
`Hall-Mark Elactronlcs Corp.
`Orlando, FL
`(305) 855-4020
`Hall-Mark Electronics Corp.
`St. Petersburg, FL
`(813) 576-8691
`
`OEOROIA
`W.A. Brown Instruments, Inc.
`Atlanta, GA
`(404) 455-1035
`Dlgllal Solutions, Inc.
`Marlena, GA
`(404) 955-4488
`Hall-Mark Electronics torp.
`Norcross, GA
`(404) 447-8000
`
`HAWAII
`Gray Associates
`Kailua, HI
`(808) 261-3751
`
`ILLINOIS
`Oytec/Central, Inc.
`Arlington Heights, IL
`(312) 394-3380
`Hall-Mark Elactronlcs Corp.
`Bensenville, IL
`(3t2) 860-3800
`
`Leasametrlc
`Culver City, CA
`(213) 670-0461
`Micro Business World
`Tarzana, CA
`(213) 996-2252
`RC Data, Inc.
`San Jose, CA
`(408) 946-3800
`Renaissance Tech. Corp.
`Concord, CA
`(415) 676-5757
`Terminal Rentals, Inc.
`Tustin, CA
`(714) 832-2414
`Terminal Rentals, Inc.
`San Jose, CA
`(408) 292-9915
`United States Data Systems
`San Mateo, CA
`(415) 572-6600
`VItek
`San Marcos, CA
`(114) 744-8305
`Waybern Corp.
`Garden Grove, CA
`(714) 554-4520
`Western Mlcrolechnology
`Cupertino, CA
`(408) 725-1662-
`
`COLORADO
`Acorn Data Products
`Englewood, CO
`(303) 779-6644
`Data Design I Development
`(303) 296-3807
`lfaii·Mark Electronics Corp.
`(303) 934-3111
`Oenver, CO
`
`FLORIDA
`W.A. Brown Instruments, Inc.
`Orlando, FL
`(305) 425-5505
`
`CALIFORNIA
`Bvte Industries
`(4'15) 783-8272
`ComputerLand Corp.
`(415) 487-5000
`Hayward, CA
`Consolidated Data Terminals
`Oakland, CA
`(415) 638-1222
`Dala Systems Marketing
`San Diego, CA
`(619) 560-9222
`Eakins Associates, Inc.
`Mountain View, CA
`(415) 969-4533
`Electronic Mktg. Specialists
`Tustin, CA
`(714) 832-9920
`Electronic Mktg. Speclatlsls
`Sunnyvale, CA
`(408) 245-9291
`Electronic Mktg. Specialists
`Reseda, CA .
`(213) 708-2055
`Electronic Mktg. Specialists
`San Diego, CA
`(619) 560-5133
`Emerson Enterprises
`San Ramon, CA
`(415) 837-8728
`Hall-Mark Electronics Corp.
`Sunnyvale, CA
`(408) 773-9990
`Hall-Mark Electronics Corp.
`San Diego, CA
`(619) 268-1201
`Leasametrlc
`Foster City, CA
`(415) 5744441
`
`ALABAMA
`W.A. Brown lnslrumenls, Inc.
`(205) 883-8660
`flail-Mark Electronics Corp.
`(205) 837-8700
`Huntsville, AL
`ALASKA
`Transalaska Data Sys. , Inc.
`Anchorage, AK
`(907) 276-5616
`ARIZONA
`Haii·Mark Electronics Corp.
`f602) 243-6601
`nternatlonal Data Systems
`(602) 231-0888
`Phoenix, AZ
`The Phoenix Group, Inc.
`Tempe, AZ
`(602) 894-9247
`Spirit Electronics
`ScoHsdale, AZ
`(602) 998-1533
`
`Page 00006
`
`

`

`and media. The drive costs only
`slightly more
`than a floppy-disk
`drive. The cost of a cartridge is com(cid:173)
`parable to the cost of a box of 10 flop-
`PY disks.
`.
`.
`This companson 1s even more
`favorable in terms of cost per byte
`because the hard-disk cartridge sup(cid:173)
`plies far more capacity per unit.
`While floppy disks can hold up to 1
`megabyte of storage before format(cid:173)
`ting, the 3. 9-inch hard disk has an un(cid:173)
`formatted capacity of 6.38 mega(cid:173)
`bytes. Not only does it carry from 6
`to 15 times more data than a floppy
`disk, it carries it more safely, sealed
`in a protective cartridge.
`While floppy-disk technology has
`matured and offers few opportunities
`for enhancement, small hard disks are
`at the beginning of their product(cid:173)
`technology cycle and will have their
`data storage capacity increased again
`and again. The cost per megabyte of
`storage is dropping rapidly.
`Like audio- and video-tape cas(cid:173)
`settes, hard-disk cartridges will be
`available in a variety of capacities.
`
`for example,
`Syquest,
`is already ·
`developing a cartridge, compatible in
`size with existing cartridges, that will
`double capacity to 12.76 megabytes.
`Regardless of capacity, these car(cid:173)
`tridges deliver better performance
`than floppy disks. Their average ac(cid:173)
`cess time is 75 milliseconds,.~<;>r from
`1.5 to 3 times faster that( floppy
`disks. The data-transfer rate is even
`·more impressive. In one second, the
`cartridge drive can
`transfer 5
`megabits, compared to the 5%-inch
`disk's% of a megabit. That's 20 times
`faster.
`Cartridge models provide better in(cid:173)
`terchangeability between drives than
`floppy dfsks. The cartridge is de(cid:173)
`signed to provide for a minimum of
`10,000 insertion/removal cycles (see
`figure 1). A closed-loop embedded
`digital servomechanism ensures car(cid:173)
`tridge interchangeability while allow(cid:173)
`ing variable sectoring. The embedded
`servo information is recorded on the
`disk and provides the sector-mark
`signals and timing information for all ·
`read/write operations.
`
`The digital servo system locks the
`read/write heads over the centerline
`of the appropriate recording track.
`More practical
`than conventional
`track-following systems, the digital
`servo leaves both surfaces free for
`data and provides flexibility in sector
`formatting. This enables system
`builders to define the number of bytes
`per sector to match any format re(cid:173)
`quirement.
`The digital servo, helped by on(cid:173)
`board microprocessor control and a
`microstepping head positioner, also
`speeds data access and improves ac(cid:173)
`curacy. The microstepping positioner
`steps in increments of 0. 9 degrees
`rather
`than
`the conventional 1.8
`degrees. The drive's microprocessor
`reads servo information, corrects for
`track alignment, and adjusts the step.(cid:173)
`per within 100 microinches, all at 60
`times a second.
`The 3. 9-inch disk drives mount
`almost anywhere-under a keyboard
`or in a
`terminal. Two hard-disk
`drives can occupy one conventional
`5%-inch floppy space. The drives are
`
`Page 00007
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`GRAPHITE , 4 JLin.
`
`MAGNETIC FILM, 3 JLin.
`
`ELECTROLESS NICKEL,
`800 JL in.
`
`ALUMINUM SUBSTRATE
`
`•
`
`HEADS RETRACT
`TO TRACK 000 FOR
`CARTRIDGE INSERTION
`
`DISK CROSS SECTION
`
`CHANNEL
`
`DOOR SLIDES TO LEFT
`FOR HEAD ACCESS
`
`MAGNETIC HUB
`
`DRIVE DOOR
`
`REGISTRATION DIAMETER
`
`Figure 1: As a cartridge is inserted into the hard-disk drive, the cartridge door slides
`open to allow access to the read/ write heads, which were previously retracted to track
`000. The disk is seated onto the drive spindle by a meta/scroll on the cartridge (not visi(cid:173)
`ble in the figure) ·and then secured by a magnetic hub. Tabs on the drive base ensure that
`the cartridge is inserted correctly and that the cartridge door is ·open. A cross section of
`the hard disk illustrates the layers of materials on the disk (not drawn to scale).
`
`only 1.625 inches high, 4.8 inches
`wide, and 8 inches deep. Their rugged
`design enables them to be used in
`portable systems.
`
`Easy Integration
`The 3.9-inch cartridge has the same
`pinouts, timing, data-transfer rates,
`and
`track/ sector
`formatting as
`industry-standard 5%-irich fixed-disk
`Winchester drives. This compatibility
`allows the use of standard Winchester
`interfacing pro(cid:173)
`controllers and
`cedures, as well as standard 5%-inch
`floppy-disk DC power supplies.
`
`Convenience
`Convenience of use is an important
`factor in the success of the cartridge.
`The 3.9-inch cartridge is a more con(cid:173)
`venient size than 8-inch floppy disks
`or larger cartridges. Just under 4
`inches in length and width and less
`than 1fz inch high, it fits in a coat
`pocket, purse, or briefcase.
`Its
`
`116 March 1983 © BYTE Publications Inc
`
`"unbendable" case is easy to handle
`and safer to mail.
`Perhaps more important is the con(cid:173)
`venience of direct access to more
`data. The user can retrieve data from
`a larger online database without in-
`
`The thin-film-plating
`technique used on
`3.9-inch hard disks
`eliminates the ·need for
`an initial purge cycle,
`which with
`conventional disks can
`take several minutes.
`
`serting and removing many floppy
`disks. This is especially important in
`such applications as accounting, in(cid:173)
`ventory control, database searches, ·
`and so on.
`
`Thin-Film Plating
`The 3. 9-inch hard-disk cartridge
`can store more data more reliably and
`in less room because it uses thin-fillll
`plating
`for
`the magnetic data.
`recording layer. While conventional
`Winchester technology must seal the
`disks away from dust, smoke, and
`other contaminan~s, the cartridge's
`graphite-coated
`thin-film metallic
`alloy needs less protection. This thin.
`film plating, with a
`lubricating
`coating
`that shields against dirt
`allows denser packing of data and
`protects the disk from "head crashes."
`This plating also eliminates the
`need for an initializing purge cycle.
`Users do not have to suffer the in(cid:173)
`convenience . of long waits before
`beginning operation. (With conven(cid:173)
`tional hard disks, filtered air is first
`blown over the surface of the disk to
`remove any possible contaminants.
`This purge cycle can take several
`minutes.) The
`thin-film recording
`medium provides greater data densi(cid:173)
`ty, a more consistent recording sur(cid:173)
`face, better magnetic resolution, less
`susceptibility to contamination, and
`greater durability than the conven(cid:173)
`tional ferric-oxide recording medium.
`Let's take a closer look at these ad(cid:173)
`vantages. Thin-film technology in(cid:173)
`creases data density.
`It
`increases
`storage capacity beyond the current
`limitations of
`the standard Win(cid:173)
`chester or floppy disk. While the con(cid:173)
`ventional medium at 20 to 30 micro(cid:173)
`inches of thickness has a maximum
`density of only 8000 flux reversals per
`inch,
`thin film
`is an order of
`magnitude
`thinner and can store
`more than 20,000 flux reversals per
`inch. This means simply that thin film
`can increase data density by 2.5
`times. Thin film maintains a more
`consistent
`recording surface. The
`conventional medium is limited by its
`uneven thickness and a soft surface
`that can be damaged in the event of a
`head crash.
`Thin film offers higher .resolution
`Expressed as a percentage, the typical
`disk recording medium has a resolu·
`tion of 65 percent. In contrast, the
`metal-film medium has a resolution
`of 80 percent. (Resolution is defined
`as the read-back voltage ratio of a
`signal recorded at twice the normal
`
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`recording frequency versus the nor(cid:173)
`mal recording-frequency signal.)
`Thin
`film
`is more durable.
`Durability~ expressed in terms of sen(cid:173)
`sitivity to head impact, is another
`critical factor. Soft oxide coatings are
`no match for a read/write head.
`When a head crashes (contacts the
`disk's surface), oxide particles are
`dislodged. These parti~les can lead to
`still more crashes or surface damage.
`Although it's not as hard as a
`read/write head, metal film is 1000
`times harder than an oxide layer. This
`greater degree of hardness
`is
`measured by the Mohs test, which
`scales degrees of hardness from 1 to
`10. Each increasing degree on the
`scale
`represents an order of
`magnitude
`increase . A
`typical
`read/write head has· a Mohs number
`of 7. The conventional medium has a
`Mohs number of 2.0 to 2.5. Metal
`film has a hardness of 5.0 to 5.5.
`Thin film is less susceptible to con(cid:173)
`tamination. With · the conventional
`medit,1m, dust particles are attracted
`
`and captured by the fluid lubricant
`used over the ferric-oxide layer. This
`presents operating problems,
`especially for oxide media used in
`Winchester-type disk drives with
`low-flying heads .. In such drives, a
`purge cycle of one to two minutes is
`required.
`·
`Some manufacturers . Sf thin-film
`disks add a layer of graphite, quartz,
`or sapphire above the metal magnetic
`layer. Depending on the loading force
`of the heads used with the disk drive,
`the protective layer can range be(cid:173)
`tween 0.025 micron and 0.1 micron.
`(The heavier the loading force, the
`thicker
`the protective
`layer.)
`Microdisk of Fremont, California, a
`sister company to Syquest, adds a
`0.1-micron graphite overcoat. The
`dry lubricant affords extra protection
`against head crashes and seals the
`metal substrate to prevent corrosion.
`
`Summary
`Floppy disks and drives still cost
`less than their nonflexible cartridge
`
`counterparts, but the cost Per
`comparable. The
`tridge user gains online
`more data,
`faster access
`greater drive reliability, and
`data integrity. These ctu·v:n••~··­
`become even · more
`hard-disk · technology and
`production improve. Users
`a single cartridge rather than a
`floppy disks will get more
`money. They ·will have the
`both worlds-the high cap·aeit:v,
`formance, and reliability of a
`rigid disk as well as the
`and low cost of a floppy disk.
`The. 3.9-inch hard-disk
`with
`thin-film plating
`floppy-disk user a better
`medium at a competitive
`predict that just as the floppy
`placed the punched card
`cassette, so will the cartridge
`the floppy. The cartridge's
`cost/performance
`ratio and
`venience for the user will
`floppy disk obsolete. •
`
`Circle 438 on inquiry card.
`
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