HANDBOOK OF RECOMMENDED ENVIRONMENTAL CONDITIONS AND HANDLING PROCEDURES FOR MAGNETIC TAPE

• Document Type: CREST
• Collection: General CIA Records
• Document Number (FOIA) /ESDN (CREST): CIA-RDP75-00163R000100050006-7
• Release Decision: RIFPUB
• Original Classification: K
• Document Page Count: 22
• Document Creation Date: December 12, 2016
• Document Release Date: March 20, 2002
• Sequence Number: 6
• Publication Date: July 1, 1972
• Content Type: PAPER

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RECOMMENDED ENVIRONMENTAL
CONDITIONS AND HANDLING
PROCEDURES FOR MAGNETIC TAPE
.TSPu!u!;SS10N HAFT
Written by Data Archives Branch
National Archives F, Records Service'
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1. 13a.cl. ;round
Federal Records Centers are accessioning magnetic tapes in ever larger
numbers and the volume is increasing continuously. Until recently,
technical information was not available on how magnetic tape reacted
to its physical environment, and the transportation, storage and
maintenance problems attendant therein. This information has recently
become available and these recommendations are based on it.
Agencies which are major users of magnetic tapes have independently
developed internal policies and procedures for tape storage, maintenance,
and protection. A number of agencies and government contractors have
separately contracted for research and development in various aspects
of magnetic tape storage, maintenance, and transportation. These
activities have not been coordinated; information acquired by one agency
is not necessarily made known to others, and the general scarcity of
standards has resulted in widely varying methods of storage, maintenance,
and transportation of magnetic tape throughout the Federal Government.
For example, surveys have indicated costs for storing magnetic tape
range from 20 cents to as high as ten dollars per reel. per year among
different users. In most cases these costs are no longer justified;
particularly since magnetic tape has constantly changing,technical
characteristics.
Magnetic tape records of all types such as Computer, Instrumentation,
Video and Audio recording tapes, fall under the provi.sior)s of Title 44
USC, and regulations issued thereunder. Hence NARS has the broad
responsibility for providing policy and procedural guidance on the
maintenance, retirement, and disposition of magnetic tape records,
just as it does for all other records of the Federal Government.
These recommendations provide procedural guidance to ADP' installations
which use magnetic tape records and particularly those which must retain
records in storage for periods in excess of one year. Adherance to these
recommendations. will result in the following benefits:
1. Less lost time due to tape read and write errors in
re.gular operations. Each read or write error costs
approximately 5 cents in main fra;,e time for each usage
of the tape. 'this means that defective tape with ten
or more errors will incur its replacement cost to a
user through extra computer time charges in about twenty
uses of the reel. Tape maintenance procedures are presented
here for minimizing total operating costs.
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2, Better recovery procedures when tape initially proves unreadable.
Surveys of computer installations over a wide range of library
sizes indicates that loss time three to ten percent due to had
tape is typical. Technical evidence shows that most users give
up too soon in attempting to read bad tape and resort to expensive
rerun procedures. More effective recovery procedures depending
on the cause of-read failure are presented here.
3. More reliable preservation of the record contents when preparing
magnetic tape for off site storage. Magnetic.tape libraries have
been growing in most installations at an annual rate of approxi-
mately fifteen percent. Just as with paper records, not all need
to be kept in the library vault at high cost. In many cases,
libraries have run out of room and installations have resorted to
using unsuitable storage space for magnetic tape records. This
has resulted in excessive costs when the tapes are used later and
the user finds that much of the data is either unreadable or readable
only with excessive error rates. The cost of proper tape preparation
and storage is minimal compared to the cost of recovery of that
information. In general, optimal preparation and storage costs
$1.77 a reel while recovery costs range from $10 to $50 a reel in
most instances.
In preparing this handbook, an extensive literature search, consultation
with magnetic tape manufacturers, engineers and experts, and visits to
over two hundred computer installations were performed. The guidelines
in this handbook are a consensus of all this experience. They have proven
effective and economical in practice at a variety of installations.
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1. PURPOSE AND SCOPE
These guidelines describe the optimal recommended physical, environmental,
and electronic standards for users of magnetic tape. They furnish pro-
cedural guidelines for. ADP installations in the handling of tape in the
domputer room environment, preparation of tapes for shipment and storage,
optimum maintenance of a magnetic tape library, and data recovery pro-
cedures.
2. APPLICABILITY
These guidelines are recommended to all Federal agencies which record or
originate magnetic tape data records as defined in 44 USC, 3301 and
regulations issued under that act,,and which either store such records
at Federal records centers or offex-such records for accessioning by the
National Archives of the United States.
Procedures contained herein will be followed by'the National Archives
and Records Service (NARS) when tapes are accessioned by the National
Archives of the United States.
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3. ENVIRONMENTAL CONDITIONS FOR TAPE STORAGE-ROOMS AND BUILDINGS
This section provides `current recommendations for environmental
conditions of tape storage facilities both in active and in-
active data storage areas. The effects of failing to meet
these requirements are discussed in Section 7, below.
3.1 Tape storage vaults and rooms shall be temperature and humidity
controlled. A positive internal air pressure is desirable to
prevent any dust intrusion.
3.1.1 Temperature range shall be. 650 - 750 + 5? (vaults), 600 - 80? F
+ 100 F (in computer rooms). Wet bulb temperature shall not
Exceed 800 F.
3.1.2 Humidity range shall be 45% 55% relative humidity, (R.I-l.)
0
5a
.
3.1.3 Dust and dirt controls shall, keep dust particles to 50 microns.
3.2 Areas used to store or condition magnetic tape should have in
operation continuous temperature and humidity recording equipment.
3.3 Magnetic tape, particularly analog. recordings of all kinds should
be protected from high intensity magnetic or electrical fields.
These include power generation facilities and transmission lines,
radar installations, bulk degaussers, and magnetic check sorters.
3.4 Metal tape storage racks should be electrically grounded and at
least a 2-foot separation should be maintained between all electri-
cal fixtures and power lines and the storage racks.
3.5 .Tape racks must be strong enough to safely bear the high weight
of the boxes of magnetic tapes.
3.6 Tapes must be stored in an upright position, not flat on their sides.
3.7 , For any storage in excess of I year, plastic cannisters which
support the reel at the hub are strongly recommended. These provide
an additional level of protection against dust, handling, environ-
mental changes and water and smoke effects when automatic fire
extinguishing equipment is triggered.
3.8 'Buildings housing tape should be protected by lightning arrestors.
3.9 Magnetic tapes containing classified data must be retained in
security areas meeting the appropriate agency record protection
requirements regarding access.
3.10 Fire protection requirements for computer rooms, storage buildings
and vaults used to house magnetic tape are described in Section 9
of these guidelines.
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4. PREPARATION OF MAGNETIC TAPES FOR LONG TERM STORAGE AND SHIPMENT
The following procedures should be followed when it is known that a reel
of magnetic tape will be stored in excess of one year. For shorter
periods, it is assumed that backup copies, either duplicates or previous
processing generations have been retained.
While it would be desirable to use most of the recommended procedures for
all tapes created during normal operations, in practice the cost is too..,
high relative to the benefits achieved for any other purpose than long-
term storage.
4.1 Quality criteria of tape selected for storage. 1
4.1.1 Pretested and certified for usage at the storage density.
4.1.2 Certified within six months before entry into storage.
4.1.3 Maximum of five write skips allowed on the tape prior to storage
entrance; none within the first 100 feet or last 200 feet.
Tapes of this quality are normally acceptable for operational use
until about ten write skips accumulate. At that time, they may be
cleaned and tested or sent out to be rehabilitated.
4.1.4 Previous tape life: less than fifty but more than four full length
tape passes.
Like many other devices, magnetic tape also needs a "break-in"
period to eliminate slight imperfections in the manufacturing process.
4.2 Processing before storage techniques.
4.2.1 Verify that an error free tape has been written by a read only pass.
4.2.2 Rewind the'tape under constant tension.
Note: For full reel recordings to the EOT marker, a backward read
will suffice for both verification and constant tension rewinding.
However, this is possible only with cline-track tapes.. For seven-
track tapes, use either a tape cleaner rewinder or precision magnetic
tape rewinder with constant low tension wind of between 6-8 ounces force.
4.2.3 Fasten leader securely with either vinyl or sponge rubber strips or
both to prevent unwinding of the tape pack. (Note: vinyl must not
be stretched).
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4.2.4 Remove write enable ring from tape-after dismounting from
the drive that wrote the file.
4.2.5 Use self-adhesive labels with minimum residue to label
tape. Write labels with any indelible medium. DO NOT USE
water soluble felt tip pens or graphite pencils.
4.3 Storage container recommendations. '
4.3.1 Container should be nonmagnetic and transparent so that
labels can be read without opening.
4.3.2 Container should be thoroughly cleaned,.dustproof, and
they should have a positive action latch mechanism. Tape
must be supported'at the hub and.not the rim.
Most cannisters on the market meet these requirements. No
.seal ring type devices meet these criteria.
4.4 Shipping container requirements.
4.4.1 Designed to resist heat, ingress of moisture and dirt and to
withstand shock.
4.4.2 Tape reel proper should be no less than three inches from
outside of case.
This will, guarantee protection against even strong magnetic
fields. Other techniques are (1) lining the inside of the
transport case with foil or (2) using special anti-magnetic
containers. The latter procedures are recommended primarily
for analog tape recordings.
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5. RECEIVING AND ACCEPTANCE PROCEDURES FOR MAGNETIC TAPE RECORDS
This section describes the recommended procedures to be followed upon
receipt of a shipment of magnetic tape records for storage and sub-
sequent reading.
Initial action upon receipt.
5.1 Remove tapes from packing box and check reel numbers against
packing list to verify shipment.
5.2 Place reels of tape in either the storage or computer room
environment for a minimum of 24 hQ.urs. This allows the tape
to come into equilibrium with its new environment. If no
visible damage is noted, the tapes'may now be used in the local
installation.
5.3 'Tapes may be subject to various environmental extremes in shipment.
Aircraft baggage holds may be subject to temperatures of minus 600 F.
Loading dock surfaces in bright sunshine may be over 1500 F. These
environmental extremes may occasionally damage tape in long distance
shipments. If damage or reading trouble occurs, see Section 6.4
for recovery procedures, particularly if a replacement reel cannot
be readily obtained.
5.4 If tapes are to be put in storage, check reading and'donstant
tension rewinding are recommended only if shipment was for a long
distance. For short. (less than 2-day transit times) distance
shipments, reels may be transferred to 'storage area immediately.
5.5 Documentation - The shipment of recorded magnetic tapes implies an
interchange of information. Two types of info:rmation.are required
for proper interpretation of the records. These are (1) Technical
information regarding density, character code, parity, operating
system labels, etc. (GSA Form 7091 may be used to record this
information) and (2) Record layouts, location of control totals,
the meaning of coded data elements, etc. A variety of forms and
documents may accompany the records. In general, the exact content
of this documentation should.be agreed upon between the sender and
recipient. Federal Information Processing Standard (FIPS)
Publication 20 contains guidelines for describing information inter-
change formats. It is available from the Government Printing Office
under catalog number C 13.52.20.
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6. S'1T7i .CSl PF1ZTO.C-S, MAIIt'1TNANCE ISM) .E:COVERY Plt(?C;I-})U('.t;S
6.1 Shelf Life - Magnetic tape is rri~ now considered an archival medium.
While isnpravements in both,. the medium and devices for reading tape have
been substantial and frequent over the years, the great majority of computer
users have at least some tapes over five years old. Studies conducted
by NAI,S show that approximately 20 percent of a given population of tape is
scrapped each. year. This is primarily due to operating problems such as
dropped reels, defect accumulation with usage clue to stretching of the tape
and dust or oxide becomning embedded in the medium, etc. Additional
scrapping of tape is clue to technological obsolescence. Most tape certified
for 556 1?PI and seven track recording has not proved suitable for nine track
3,200 PC;I recording.
In addition, there are actual effects of deterioration in storage due to
time alone even when magnetic tape is stored in optimal environments. For
these reasons, the present shelf life of magnetic tape is estimated at
about twelve years. Magnetic tapes being produced in 1971 (particularly the
premium tapes) appear to have a shelf life which may approach twenty years.
All studies of magnetic tape stored for extended periods of time show that
errors, both temporary and permanent, tend to increase with Vhi,- in storage.
The buildup rate of errors in storage is approximately an exponential
function.. That is, tape errors double with each year in storage. These
error rates start at less than one temporary error per reel in,the first
year for tapes manufactured prior to 1967 to less than one error per four
reels in current production tapes.
The mechanism by which magnetic tape deteriorates in storage is as follows:
(1) Minor defects become permanent errors clue to plastic cold
flow from nonuniform and excessive stress build-up in the
tape when the tape is subjected to changes in temperature
and humidity. These defects are commonly referred to as
lipped edges, hard bands and defect embossments (dimples).
(2) Different rates of expansion in the length and thickness
directions of the tape clue to temperature and humidity
changes produce stresses which permanently deform the
tape. These defects are commonly referred to as
cinching or windowing.
I pperimenta.l evidence s!-r;,isthat current production magnetic tapes are less
sensitive to these environmental changes than earlier tapes. Proper periodic
maintenance of magnetic tape In storage will keep the development of errors
on magnetic tape recordings down to a negligible level. alld detect trouble
in time to recover all of the recorded information. The following sub-
section describes these procedures:
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6.2 Periodic Rewinding and Physical Inspection - The buildup of errors
can be largely eliminated as long as the medium has not deteriorated.
This is accomplished by periodic rewinding under constant or prograiied
tension. Precision winders are manufactured by several manufacturers
which will unwind and rewind a 10-1/2 inch reel in approximately five
minutes. This operation will redistribute the stresses in the tape and tend
to eliminate some imperfections that have been formed during storage. The
recommended period between such operations is one year. At the same time,
any physical deterioration can be noted by the operator and further testing
of suspect tapes initiated. See Section 6.4 for criteria to be used in
visual inspection of magnetic tapes.
6.3 Periodic Test Reading of Sample Tapes from Inventory of Stored Files -
Magnetic tapes do not fail suddenly. Rather, deterioration is noticed by a
gradual accumulation of read errors both of the temporary and permanent type.
Therefore, annual read checks of a sample of tape records is sufficient to
spot deterioration of recordings and to allow for corrective action and
recopying to occur.
At least one tape from every file should be test read on an annual basis.
This should be clone prior to annual rewinding. If the reel proves to
have more than temporary read errors, the entire file should be test read
and, if necessary, recopied on a reel for reel basis for any reel which
shows permanent read errors. Temporary errors on a reel can be usually
eliminated by a cleaning and rewinding operation. Such reels can then
be check read again to see if the errors are eliminated. If they have
been eliminated, the tape can be passed and returned to the inventory.
If not, data recovery procedures may be instituted as described in
Section 6.4 for recreating a new copy.
If a tape has even one permanent read arrcr (i.e. the tape drive hangs up on
a particular block, data recovery procedures should be immediately instituted
and a new copy created.
For very large files, no more than a five percent sample of the reels need
be test read. This five percent recommendation should also he followed in
such cases where files are cumulative and augmented periodically. Examples
"would be. any data recording activity which generates in excess of twenty
reels annually. The entire series of tapes for a given year can be treated
as one file for inspection purposes.
6.4 Visual Inspection Criteria - Causes and Recovery Procedures - This
section describes the types of conditions which can definately generate
unrecoverable read errors in a -~ubscquent operation. Some of these conditions
can be seen while the tape is being pulled out from its cannister while others
can be seen only when the tape is mounted and has hung up during a read
operation
6.4.1 Defects visible while tape is removed from cannister but
has not been mounted on a tape drvie -
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6.4.1.]. Poor wind.- This is manifested in two ways. Cinching is
a separation of adjacent layers of tape in the wrap with,
a corresponding crosswise wrinkle in the tape. This
condition will lead to errors in the section of tape
around the defect. It is most common in files shorter
than a full reel. This trouble is also located mostly
near the end of the file. In full reel recordings,
the condition is caused by excessive temperature and
humidity variation during shipment.
The second visible symptom of a poor wind is protruding
layers of tape from the pack. This will;cause edge
damage and is more severe in nine track than seven track
recordings. The tape pack should also be equidistant between
the reel. flanges. If it is not, there is a strong possibility
that the reel was mishandled in shipment such as,dropping or
left lying on its side in a high vibration shipping mode.
Both of these symptoms, if seen, require an immediate pass of the
file on a cleaner rewinder followed by a day in dead storage for
stress relief and a subsequent rewind pass. After the second
rewind pass, the reel may be check read to see if any data loss
occurs.
6.4.1.2 Broken flange, hub, or cannister - All are indications of ex-
cessively rough handling and shipping or shelving operations. If
the reel is broken, the tape pack should he immediately transferred
to a new reel before any testing and recovery procedures are
attempted. After. the file'is mounted on a new reel, perform the
corrective procedures of 6.4.1.1, above.
6.4.1.3 Color changes or spots in the tape pack as seen from the side -
his is almost invariably a sign of a chemical reaction between
the oxide binder and whatever may have been packed with the reel.
Chemicals may he in any of the following items: adhesive on labels,
inks, felt tip pens, paper and the rubber or vinyl stoppers which
hold the tape leader down.
Atone time or another, almost all of these substances have been
known to generate gases which have reacted with the binder
composition and resulted in oxide pull-out. No recovery pro-'
cedures can salvage data lost in this manner. The only recourse
is to recreate the tape from backup copies. For this reason, the
only extraneous items which should be packed with a tame reel in
a cannister are new stoppers and self adhesive labels designed
specifically for computer"tapes.
6.4.2 Defects visible at point where tape proves unreadable - Causes and
Recovery Procedures .- Some visible defects are curable to the extent
that a good copy of a file may be made. Others by their vary nature
indicate a total loss of recording at the point of trouble. Under
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flTese conditions, if only one or a few blocks of data are lost,
some file or record reconstruction may be possible by printing
the defective block(s) out and determining if any significant
data was lost. Reconstructing lost records at best is a tedious
job^and should only be attempted if for some reason no backup
file exists.
6.4.2.1 Oxide pull-out - No recovery possible. The visual symptom
is a spot on the tape with missing binder which may have
been transferred to an adjacent layer of tape. Clean the
tape drive after removing the reel.
6.4.2.2 Surface contamination and dimples - Dirt wrapped into a
reel will usually create d_iq)les over time in adjacent layers
of tape. Remove the tape from the tape drive and exercise
it by two to five cleaning passes followed by a one-day
stress relief storage period. Following this period exercise
the tape for up to twenty passes on the drive which is to
read it.
6.4.2.3 Creases and scratches - iJse.same procedure as in 6.4.2.2, above.
Creases are usually caused by poor wrap in the tape pack.
Iliese are aggravated by poor handling and environmental
conditions.
6.4.2.4 Embossments in tape wrap - Under high pressure generated by
both high temperature and hlnnidity and cycling, the end-of
tape marker can generate embossments and irregularities in
the last few wraps of tape in a reel. To recover data, use
procedure specified in 6.4.2.2, above.
6.4.2.5 Torn tape in middle of pack - This is a sure sign'that the tape-
has been subject to temperature and humidity extremes either
in storage or transit. The block of data at that point is lost
and only record reconstruction can be instituted after splicing
temporarily and using the procedures of 6.4.2.2 to salvage the
rest of the tape.
6.4.2.6 Adhesion and blocking - Adhesion of adjacent tape layers is due
to static buildup on tape surfaces and storage of tapes in
extremely dry conditions. Low humidity conditions in much office
space and computer rooms is due to not procuring humidifiers in
conjunction with air conditioning equipment. ?ecent desif'ns of
both tape drives and tapes have greatly reduced this phenomenom,
but it is still occurring with tape drive designs of most second
generation computing equipment and with magnetic tapes procured
prior to 1967-8.
Blocking has no recovery procedure. Excessive humidity and
temperature will cause the ruler half inch of a tape pack to
become a solid mass of rrrylar.'and binder. It can only be pre-
vented by proper environmental conditions.
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6.4.3 Unreadable or excessive error rate on tape with no visible
defects - There are,two'possible causes of this. One is
the presence of strong magnetic fields in the tape storage
environment. The two primary sources of magnetic fields
strong enough to affect recorded tape are magnetic ink
check sorters and tape degaussors.
Magnetic. ink. check sorters have very powerful magnets used
__.to e~ tract staples and paper clips from checks entering the
sorting mechanisin. These can damage recordings on tapes
brought to within six inches of the magnet. 1agnetic tape
bulk degaussers are designed to generate very large external
magnetic fields to erase tape and will damage recordings
within a distance of six inches. No other magnetic fields
commonly found anywhere are strong enough to damage magnetic
tape recordings.
The same sylllptcns are manifest when a tape has become skewed.
T'liat is, there is some curvature in the tape Which results in
misaligned bits in particular frames while the tape is under
the read head of the drive.
Differentiating between these two causes requires the aid of a
field engineer servicing, the equipment. - Oscilliscopes can
determine whether the trouble is due to either reduced -Unplitude
of the recording or misaligned bits. Once the cause of the
reacting trouble has been determined the recovery procedure is
different in each case.
Data recovery on partially erased reels requires an adjustment
of the tape drive electronics. in general, only the local
field engineer can perform this adjustment.
Read trouble with skewed 'tapes is most prevalent at 300 BPI
recording densities. The recovery procedures are the same as those
given for the visible defects in Section 0.4.2; namely, several
cleaning passes, each followed, by a stress relief period of one
day and up to twenty passes of the tape on the drive which is to
'read it. These operations tend to straighten out the tape.
6.S' Othet-'recOver procedures Some tape drives have. the capability
cif~xcacfzn? Frnc,~7:ards. ff this is so, it is frequently possible .
to read c 1 a 1' OT's rot.:,. bl.y in this rode t-hall in the 1_or1',r' Cl. diu coon
It has also been observed that tape which may be unreadable on one
type of drive may read perfectly on another type or model.. For
example, the dynamic stress on 'tape differs considerably depending
on the acceleration and speed of the drive mechanism. Recordings
that marginally meet specification limits may not be readable on
.another drive which is itself marginal in ad jusuient. If repeated
exercising of the tape gives unreliable reading of the file, it
is possible to adjust the drive to read a particular recorded tape.
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In general, only the field engineer can diagnose these conditions and
make the necessary adjustment. It is obvious that these procedures
are costly and should be undertaken only if the data recovery costs
are less than recreating the file from backup copies.
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7. EFFECT OF POOR FNVIRONNTNTAL CONDITIONS ON MAGNETIC TAPE AND RECORDINGS
Most tape manufacturer reconnnendations for storing magnetic tape cite a
temperature range of, between 60 to 90 degrees Fahrenheit and a humidity
range of between 20 and 80 percent. Typical published tolerances are
plus or minus ten degrees on temperature and plus or minus ten percent
on humidity. These envirorunental conditions are similar to those specified
for the computers themselves.
Experimental evidence shows that the environmental conditions listed below
usually cause tape reading trouble in a matter of weeks.
7.1. Temperature and humidity cycling in warehouse-grade space -
Magnetic tape has a relatively high coefficient of expansion with
respect to both temperature Wild hi.miidity. This means that very
large stresses are built up in the tape pack when it is subjected
to temperature and' himiidity changes. This is true even though
the actual temperature and himdi,dity values may he within the limits
specified for the tape. typical conditions almost guaranteed to
cause trouble are cycling between 55 and 95 degrees Fahrenheit
during a six-month storage period or between fifty. and ten percent
hu.miidity. A warehouse may have temperature controls but does not
usually have provision for adding humidity in the winter. Under
these conditions, tape will shrink. 'T'his shrinking causes increased
pressure inside the pack and tends to set dimples in the tape in layers
adjacent to imbedded dirt. The result on subsequent read attempts is
individual frame parity errors.
Two other effects of such cycling; are a result of storing tapes removed
directly from tape drives. If the recording is less than a full reel.,
there is a winding tension difference between adjacent layers of tare
at the end of the last recording made. The environmental cycling
causes a shift of the entire pack at this Point generating wrinkled
tape near the end of the file.' ,1"hi.s phenomeni.nn is known as cinching.
The uzforti.mate effect of this condition is that the trouble does not
manifest itself until near the end of the program subsequently using
the file.
The. second effect of cycling is on tapes with protruding layers of
tape in the middle of the pack. Nine track tapes are particularly
sensitive to edge damage from handling but in addition, these changes
in environmental conditions cause unequal compression of these layers.
This results in. such defects as tape creases and l:ilm,ed edges. In
general, several. feet of 'tape can be damaged this way making recovery
of information very difficult.
7.2 Excessive temperature and himia.dity - This combination of conditions
occurs in non-air-conditioned.space. The effect is to cause blocking
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of the tape and layer to layer adhesion. The newest tapes are less
sensitive to these conditions than older tapes, particularly those
purchased prior to 1967. The effect on a subsequent read attempt
is for the tape to. tear about halfway through the reel. This occurs
because the layers of tape adhere with more force than the vacuum
coltmins on typical tape drives can generate. This occurs both in
warehouses in winter and some computer rooms without proper environ-
mental controls.
7.3 Very dry conditions - This causes adhesion of adjacent layers of tape
clue to - static ' nuii dup on the tape backing surface. The symptoms
are the same as discussed in the i.nunediately preceding paragraph.
One additional trouble this kind of tape will generate is an attrac-
tiveness for dust. Initial read attempts may be satisfactory but a
second usage of the tape will reveal parity errors of a temporary
kind. The tape may read successfully but only at the expense of excessive
reread attempts.
drive will have various unequal stress and strains wound into it while on
the drive. in storage, these will tend to equalize themselves by stret~.h-
ing of the tape in unequal amounts These chancres are reversible up to a
point and can be virtually eliminated with periodic rewi.ncing at one-year
intervals. If this is not done, the most characteristic defect will be' a
curvature in the tape leading; to misal.i.;.nmcnt of the tape when going under
the read heads or actual skew (misali(,,nment of the individual recording
tracks in time while under the read head). The symptoms are parity trouble
occuring in bunches in the middle of the tape.
of cold flow over time. flagnetic tapie taken. directly from a computer tti.pe
Effect of time - Since macnetic tape is a plastic, it exhibits the pher_-.)menun
7.5 Strong magnetic fields - Tapes must be stared. to avoid very close nroximi.ty
ausse
to stray, highly powered magnetic fields , such as fi )U11-7
produces a highly concentrated field of 1500 oersteds. Laboratory tests
have been conducted to detennine what would constitute adequate protection.
It was found that field strengths of more than 1500 oersteds would not
be encountered in ordinary storage or shipping situations. A;agnetic
field. intensity decreases rapidly with distance ,from the source. It was
found that the degree of erasure at a distance of (3) three inches was
almost immeasurable and that a 1500 oersted 00 cycle clectro-r.nagnetic
source is reduced to the 50 oersted point. To obtain this data the magnetic
tape was first exposed to an electromagnetic field at varying distances
and erasing effects measured. It was found that it was extremely hard
to obtain any meanin?ful measurements at more than (3) three inches from
the magnetic source. All tests have indicated that magnetic field strengths
within the tape of 50 oersteds or less cause no measurable erasure and the
conclusion was reached that there is a very high probability that magnetic
tape is unaffected by stray magnetic fields. To obtain accidental erasure
protection during shipment or during storage of mnv-a?netic tapes, simple
physical spacing, of 3 inches or more from any electro-magnetic source
is the easiest and least costly method suggested.
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8. EFFECTS OF RECORDING DENSITIES AND 1` N'1iFACfIIRING TTCILNIQUES ON MAGNETIC TAPE
Magnetic tape drives and reels are components of a total recording system.
Although their external appearances have not changed significantly since
1955, there have been, in fact, dramatic changes in the reliability and
performance capabilities of this information recording technique. This
section describes factors useful to magnetic tape users regarding the
changes that have taken. place in tape characteristics and recording
techniques over the years.
8.1 Density effects - The earlier tapes were recorded at densities of
100 to 250 bits per inch using the NRZI (Non return to zero) recording
technique. These densities are now obsolete and are seldom used in
new equipment, although many drives exist which will read them.
Troubles occurring at these densities are the result of old tapes.;
The problems of older tapes will be discussed in 8.2, below. With new
tapes, these densities have not been a problem. Quite successful
results are on record of tapes recorded in 1960 and read error free
in 1.970 with no more precaution than storing the tape in a computer
room environment.
At 556 BPI (bits per inch) which began to be used in the late 1950's
and early 1960's, no problems have been noticed after even eight to
nine years if the tape used was the best available At that time.
Trouble free recordings have been observed in those installations
that were able to buy premium instead of standard grade computer
tape. The recording technique is also the NRZI technique and recent
recordings made at this density appear to be effectively readable
for the life of the physical tape as long as tape drives are available
to read them.
Almost all trouble reports center around 800 BPI NRZI recordings.
This is true for both 7 and 9-track tapes. As explained by magnetic
tape and tape drive engineers, the primary cause of reading trouble
even after a few months is the fact that for the NRZI recording
technique, 800 BPI represents the upper limit of the technology.
The best current tapes have a dynamic skew of one microsecond at
112 inches per second reading speed. This is a significant fraction
of a wave length and means that very little, stretching or shifting
of tape is needed to generate. a good deal of reading trouble. For
this reason, 800 BPI is not recommended as the density of choice for
either long term storage or information interchange.
y4 At present (1971) good results are being achieved with 1,000 BPI phase-
encoded tape. In' fact, better results are being achieved at 1,600 BPI
even in dual density tape drives whore both 800 and 1,600 BPI density
recordings can be-made. Sixteen hundred BPI recordings are far less
sensitive to tape degradation such as skew and dirt for the following
reasons:
- The tape drive read mechanism contains a skew register
specifically designed to, compensate for dynamic skew.
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In effect, phase encoding has a potential upper density
recording limit of ten thousand BPI. The net result is
a more reliable recording technique and medium combination
than NP.ZI is at present.
This recording technique is also less susceptable to
dropouts. For example, in testing and certifying magnetic
tape for NIRZI recording, a 50 percent loss of signal is
marginal for any recorded bit. In phase encoding, an
80 percent loss of signal is marginal. This means a
reduced sensitivity to dirt and other handling damage.
In summary, the optimal densities at which to store magnetic tape,
records are either 556 or 1,600 BPI depending upon the particular
computer. On the basis of cost involved in maintaining tapes in
storage, the large advantage in space that high density offers
over lower densities makes it a better practive to follow.
8.2 Magentic tape quality over the years - Magnetic tape has been
improved greatly in the last fifteen years. Even the lowest grades
of current production computer tape is superior to the premium
tapes of even eight years ago. The following paragraphs describe
the changes in magnetic tape quality factors during the 1960's.
8.2.1 Oxide shed - Early tapes generated many dropouts due to
shedding of particles of oxide from the surface coating.
These particles were rubbed off at the read-write head
and would periodically drop off in clumps and get wound
into the tape wrap. Newer tapes have almost eliminated this
problem'by being much smoother. Current tapes have a surface
roughness of one to six micro-inches compared to double that,
in the early 1960's. Formulation, of the binder and oxide
grain itself is also much better,resulting in less trouble
and wear from this source.
8.2.2 Deterioration of oxide coating - Some.tapes manufactured
between 1962 and 1964 had fungicides in their formulation.
Many of these tapes have deteriorated in storage since the
y mgicide was not a stable compound. The symptom here was
for the entire coating to peel off in chunks. This manufacturing
practice was eliminated in all post 1964 production tapes.
8.2.3 Skew and hacking stability - Current premium production tapes
have a dynamic skew of one microsecond at 112 inches per second
tape speed. Standard tapes have a dynamic skew of 2 micro-
seconds. Earlier tapes had much higher skew values. It is
this dynamic skew specification which makes tapes interchangeable
between installations or stable in storage and is a function of
the quality control and process stability in manufacturing
mylar backing.
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8.2.4 Sensitivity to environmental changes in temperature and
humidity - Cycling tests show that both temporary and
permanent errors have been reduced by 75 percent between
1965 and 1968 production tapes. Even if some dirt is
embedded in current tape, only one or two wrap layers
will show'dimpling. Also fewer cleaning and exercising passes
are required to restore the surface of the tape for data
recovery to take place. Additional changes in the coefficient
of friction between the backing and oxide surfaces result in
less defects showing up after poor environmental storage;
.particularly cinching and tearing.
$.2.5 Sensitivity to dryness - Tapes.stored in low humidity have
often generated much static electricity on the tape surface.
Over the years, surface resisitance of both oxide and mylar
surfaces have been reduced. The result is a. bleed off of
the electrostatic charges and less attraction for atmospheric
dirt or adhesion of adjacent tape layers during a read operation.
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9. FII E PRUTE( ICN
9.1 Magnetic tape, tape reels, and containers are all extremely
susceptible to heat, steam, and fire and also are potential
contributors to fire. Tape reels and containers should be
made of fire resistant materials when possible. All rooms.
and areas in which tapes, reels, and containers are to be
used or stored must, therefore, provide for protection
against fire as one of the major considerations.
9.1.1 No open flame (matches, cigarette lighters) or smoking
should. be allowed in tape handling areas. Smoke particles
deposited on the tape have been known to cause dropouts.
9.1.2 Tape vaults must be insulated to provide fire resistance
limits tip to 1500 F temperature and 85% relative hiunidity.
9.1.3 Combustibles such as wood, paper, volatile cleaning fluids,
etc. , must be kept to a mthii?uun in tape storage areas.
9.1.4 The use of CX)2 (Carbon Dioxide) extinguishers and 3-120 (water)
are reconaiended in fire; extinguishment. The use of water
requires that all tapes must be carefully dried within 24
hours to avoid "cupping and blocking."
9.1.5 Fire protection requirements shall be in accordance with
"Fire Protection for Essential. Electronic Equipment" ([P-1)
issued by the Federal Fire Council, (1969 revision).
1.0. EFFECTS OF NUCLEAR 3J\DTATTON
10.1 Physical Effects
Studies have indicated that the effects of gmmna and/or beta
dosage on the physical and magnetic properties of magnetic
tape causes little or no physical damage up to the 51)-magarep
level: Above the 50-megarep level. Polyester base materials begin
to show sonic physical deterioration. The tape backing and
coating will show significant cmbrittlement (easily broken,
cracked or snapped) and life of the tape could be reduced by
as much as 60%.
10.2 Magndtic Properties
It has been determined that magnetic tape will be unaffected by
nuclear radiation until the dosage approaches a level at least
100 megareps (Note: Megarep equals -1 million roentgen equivalent
physical). Radiation of the magnitude would oply increase the
layer-to-layer "print-through" bv anproximately 4 (11). This
print.-through effect is so slight that it is not considered
serious, and would not prevent retrieval of the information
stored on the tape.
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This amount of radiation, 100 megarep,.will also have some
effects on the tape coating. The effect of Neutron bombardment
on the coating (iron-oxide and binder) would no doubt be limited
to activation of the iron-oxide coating, which would produce a
radioactive isotope that itself might become another source of
radiation. It is theorized that such activation would not
produce a change in the overall magnetic properties of the
coating.
11. HANDLING TAPE IN ACTIVE AREAS
11.1 Tapes should not be touched with the fingers, (the use of
lint-free gloves is recommended where an unusual amount of
handling occurs).
11.2 Working areas should be devoid of all substances that can
adhere to the tape causing dust and lint to collect. Among
those substances are such common items as cigarette ashes,
food, drinks, floor and other types of waxes.
11.2.1 No eating or smoking in computer or tape storage areas.
Food particles can be just as harmful as-smoke particles.
11.3 Tapes should be handled in a careful manner, not pulled,
yanked, squeezed, or scratched, and they should be protected
against heat changes and fire hazard during all transportation
operations.
.11.4 Tapes, reels or containers should not be thrown or dropped,
when either empty or full.
11.4.1 Replace any old or damaged reels and inspect all take-up
reels on tape drives weekly.
11.5 The following page contains a check list for magnetic tape
users and custodians. It is a , su unary of critical factors
involved in. the long term preservation of magnetic tapes.
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SUGGESTED CHECK LIST
Active Tape Area
1. Fire proof building
1.
2. CO2 extinguishers
2.
3. No open flames
3.
4. No smoking
4.
5. Dust free conditions
S.
6. No paper chips
6.
k
(
eypunch and printers)
7. 'No food
7.
Temp. 700 F ? S?
10. Humidity 500 ? 5?
1.
11. No magnetic fields
2.
12. Positive internal
3.
i
a
r pressure
4.
Storage Cabinets or Racks
5.
1.
Shelves adequate in strength
2
D
f
.
ust
ree conditions
6.
3
2'
.
clearance to any
l
i
f
e
ectr
cal
ixture
7.
4.-
Electrically grounded
5.
Vertical stacking of tape
6.
No magnetic door latches
1.
Tape Containers
2.
3.
1.
Cleaned bebtieen use
4.
5.
2.
Flub supported
6.
7.
3.
Dust tight
8.
1.
2.
3.
Inactive Storage Areas
Fire proof and protected
No fire hazards
Dust free conditions
Temp. 700 F + 50
Humidity 500 5?
No close magnetic fields
Positive internal
air pressure
In Transit - short time period
Fire resistant packaging
Dust protected
Careful handling
No bumping
Temp. SO-90? F ? 10?
Humidity 40-60o ? 100
Inspected before and
after shipment -
Tape handling
No finger contact
Lint free gloves
Careful hmi.dling
Clean transports every shift
"Low-wind tension"
Rewound annually
Certified. product
Receiving inspection
Tape Reels
o sharp edges
Undistorted flanges and hub .~
Labeled; properly _
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