1、ANSI INCITS 157-1987 (R2003)(formerly ANSI X3.157-1987 (R1998)for Information Systems Recorded Magnetic Tape forInformation Interchange 3200 cpi (126 cpmm),Phase EncodedANSI X3.157-1987 American National Standard for Information Systems - Recorded Magnetic Tape for Information Interchange - 3200 cpi
2、 (126 cpmm), Phase Encoded Secretariat Computer and Business Equipment Mapufacturers Association Approved June 15, 1987 American National Standards Institute, I nc AmericanNationalStandardApproval of an American National Standard requires review by ANSI that therequirements for due process, consensu
3、s, and other criteria for approval havebeen met by the standards developer.Consensus is established when, in the judgment of the ANSI Board of StandardsReview, substantial agreement has been reached by directly and materiallyaffected interests. Substantial agreement means much more than a simplemajo
4、rity, but not necessarily unanimity. Consensus requires that all views andobjections be considered, and that a concerted effort be made toward theirresolution.The use of American National Standards is completely voluntary; their existencedoes not in any respect preclude anyone, whether he has approv
5、ed the standardsor not, from manufacturing, marketing, purchasing, or using products, processes,or procedures not conforming to the standards.The American National Standards Institute does not develop standards and will inno circumstances give an interpretation of any American National Standard.More
6、over, no person shall have the right or authority to issue an interpretation ofan American National Standard in the name of the American National StandardsInstitute. Requests for interpretations should be addressed to the secretariat orsponsor whose name appears on the title page of this standard.CA
7、UTION NOTICE: This American National Standard may be revised orwithdrawn at any time. The procedures of the American National StandardsInstitute require that action be taken periodically to reaffirm, revise, or withdrawthis standard. Purchasers of American National Standards may receive currentinfor
8、mation on all standards by calling or writing the American National StandardsInstitute.Published byAmerican National Standards Institute11 West 42nd Street, New York, New York 10036Copyright 1987 by Information Technology Industry Council (ITI)All rights reserved.No part of this publication may be r
9、eproduced in anyform, in an electronic retrieval system or otherwise,without prior written permission of ITI, 1250 Eye Street NW,Washington, DC 20005.Printed in the United States of AmericaForeword (This Foreword is not part of American National Standard X3.157-1987.) This standard presents the mini
10、mum requirements for the physical and magnetic inter- changeability of 1/24nch (12.7-mm) -wide digital magnetic computer tape recorded at 3200 cpi (126 cpmm) on 9 tracks using phase encoding (PE) recording techniques. The tape is to be used for information processing systems, communication systems,
11、and asso- ciated equipment utilizing a standard code for information interchange. This standard evolved from a need to pack more data on a standard 1/24nch (12.7-mm) computer tape reel with a minimum impact on system architecture. This was accom- plished by adopting the existing recording format 160
12、0 cpi (63 cpmm), PE, as described in American National Standard for Information Systems - Recorded Magnetic Tape for Information Interchange (1600 CPI, Phase Encoded), ANSI X3.39-1986, and modifying the recording density and ID burst location to achieve twice the recorded flux transition density. Th
13、e result is a new standard recording format providing about a 95percent increase in data packing density, while maintaining integrity of the widely adopted 1600cpi (63cpmm), PE, data flow. Although this standard doesnt deal with the machines that record and reproduce this data, it should be noted th
14、at some computer tape drive suppliers are providing features in their products to write and read the new 3200-cpi (126-cpmm) recorded tapes over the same interface used for preexisting 1600-cpi (63-cpmm) tape drives. The Technical Committee on Digital Magnetic Tape, which developed this standard, co
15、n- sists of a number of experienced and qualified specialists on the recording of digital infor- mation on magnetic tape. In the development of this standard, careful consideration was given to current practices, existing equipment and supplies, and the broadest possible ac- ceptance, and to providi
16、ng a basis for future improvement in the use of the medium. This standard was approved as an American National Standard on June 1.5, 1987. Suggestions for improvement of this standard will be welcome. They should be sent to the Computer and Business Equipment Manufacturers Association, 3 11 First St
17、reet, NW, Suite 500, Washington, DC 20001. This standard was processed and approved for submittal to ANSI by the Accredited Stan- dards Committee on Information Processing Systems, X3. Committee approval of this standard does not necessarily imply that all committee members voted for its approval. A
18、t the time it approved this standard, the X3 Committee had the following members. Richard Gibson, Chair Donald C. Loughry, Vice-Chair Catherine A. Kachurik, Administrative Secretary Organization Represented Name of Representative American Library Association. . American Nuclear Society AMP Incorpora
19、ted Association of the Institute for Certification of Computer Professionals. AT 1600 CPI, PE; and 6250 CPI, GCR) ANSI X3.40-1983. In that related standard, the following sections are dealt with in detail. general requirements, definitions, tape physical and magnetic requirements, tape reel, and wri
20、te-enable ring. Compliance with ANSI X3.40-1 983 is a require- ment for information interchange. 1.2 Purpose 1.2.1 This standard defines the requirements and supporting test methods necessary to ensure interchange at acceptable performance levels. It is distinct from a specification in that it delin
21、eates a minimum of restric- tions consistent with compatibility in interchange transactions. 1.2.2 The performance levels contained in this stan- dard represent the minimum acceptable levels of per- formance for interchange purposes. They therefore represent the performance levels that the interchan
22、ged items should meet or surpass during their useful lives and thus define end-of-life criteria for interchange pur- poses. The performance levels in this standard are not intended to be employed as substitutes for purchase specification. 1.2.3 Wherever feasible, quantitative performance levels that
23、 shall be met or exceeded in order to comply with this standard are given. In all cases, including those in which quantitative limits for requirements falling within the scope of this standard are not stated but left to agreement between interchange parties, test methods and measurement procedures s
24、hall be used to determine such limits. 1.2.4 U.S. engineering units are the original dimen- sions in this standard. Conversions of toleranced dimen- sions from customary U.S. engineering units (similar to British Imperial Units) to SI units have been incorpo- rated in this standard in accordance wit
25、h Method A as described in American National Standard Metric Prac- tice, ANSI/IEEE 268-1982 and in International Stan- dard for Tolerance Dimensions - Conversion from Inches into Millimetres and Vice Versa, IS0 370-1975. Method A, as described in ANSI/IEEE 268-1982, should be used to achieve economy
26、 unless a require- ment for absolute assurance of fit justifies use of Meth- od B. In the national standards of IS0 member bodies, additional rounding may be done to produce “pre- ferred” values. These values should lie within or close to the original tolerance. 1.2.5 Except as indicated in 1.2.3, i
27、nterchange parties complying with the applicable standards should be able to achieve compatibility without need for addi- tional exchange of technical idformation. 2. Referenced and Related Standards 2.1 Referenced American National Standard. This standard is intended for use in conjunction with Ame
28、r- ican National Standard for Information Systems - Coded Character Sets - 7-Bit American National Stan- dard Code for Information Interchange (7-Bit ASCII), ANSI X3.4-1986. When this referenced standard is superseded by a revision approved by the American National Standards Institute, Inc, the revi
29、sion shall apply. 7 AMERICAN NATIONAL STANDARD X3.157-1987 2.2 Related Standards. The standards listed here are for information only and are not essential for comple- tion of the requirements of this standard. ANSI X3.40-1983, Information Systems - Unrecorded Magnetic Tape for Information Interchang
30、e (9-Track 800 CPI, NRZI; 1600 CPI, PE; and 6250 CPI, GCR) ANSI/IEEE 268-1982, Metric Practice IS0 370-1975, Toleranced Dimensions - Conversion from Inches into Millimetres and Vice Versa 3. Definitions 3.1 Master Standard Amplitude Reference Tape. An amplitude reference tape that has been selected
31、by the National Bureau of Standards (NBS) to establish the reference level for average peak-to-peak signal ampli- tude output when recorded at a specific physical re- cording density on a master measurement system. 3.2 Secondary Standard Aplitude Reference Tape. An amplitude reference tape that has
32、been calibrated by the NBS with respect to the reference level of the master standard amplitude reference tape. 3.3 Standard Reference Current. For the physical re- cording density of 6400 ftpi (252 ftpmm), the stan- dard reference current (r,) is the minimum record current that, when applied to an
33、amplitude reference tape, causes an average peak-to-peak signal amplitude output equal to 95 percent of the maximum average amplitude. 3.4 Standard Measurement Current. For the physical recording density of 6400 ftpi (252 ftpmm), the stan- dard measurement current (Im) is 1.39 to 1.41 times the valu
34、e of I,. 3.5 Standard Reference Amplitude. The theoretical average peak-to-peak signal amplitude output from the NBS master standard amplitude reference tape when it is recorded with Im on the NBS measurement system at the physical recording density of 6400 ftpi (252 ftpmm). NOTE: The NBS master and
35、 secondary standard amplitude reference tapes (SRM 6250) are certified by NBS solely at the ohvsical recording densitv of 9042 ftni (356 ftnmm). Theie Is no standard ieferenc-e amplitude-reference-level main- tained by NBS for the physical recording density of 6400 ftpi (252 ftpmm). The average peak
36、-to-peak signal amplitude output for the physical recording density of 6400 ftpi (252 ftpmm) can be defined as a percent level of a theoreti- cal standard reference amplitude by finding the average peak-to-peak signal amplitude output at 1, for the physical recording density of 6400 ftpi (252 ftpmm)
37、 on an SRM 6250 tape and assigning to that output the same percentage of output that has been certified by NBS for the physical recording density of 9042 ftpi (356 ftpmm) on that tape. 3.6 Beginning-of-Tape (BOT) Marker. (See Figure 1.) A photo-reflective marker placed on the tape for the purpose of
38、 indicating the beginning of the usable recording area. 3.7 Block. A group of contiguously recorded charac- ters considered and transported as a unit containing one or more logical records. Blocks are separated by an interblock gap. 3.8 Data Density. The number of data characters stored per unit len
39、gth of tape, e.g., characters per inch (cpi), characters per millimeter (cpmm). 3.9 Physical Recording Density. The number of re- corded flux transitions per unit length of track, e.g., flux transitions per inch (ftpi) or flux transitions per millimeter (ftpmm). 3.10 Flux Transition Position. A poin
40、t on the mag- netic tape that exhibits maximum free space flux den- sity normal to the tape surface. 3.11 Flux Transition Spacing. The distance on the magnetic tape between flux transitions. 3.12 Interblock Gap. A DC-erased section of tape separating blocks of information. 3.13 Postamble. A group of
41、 special signals recorded at the end of each block for the purpose of electronic synchronization. 3.14 Preamble. A group of special signals recorded at the beginning of each block for the purpose of elec- tronic synchronization. 3.15 Skew. The deviation of bits within a tape charac- ter from the int
42、ended or ideal placement, which is per- pendicular to the reference edge. 3.16 Tape Mark. A special control block recorded on magnetic tape to serve as a separator between sequences of recorded blocks treated as a unit. A master standard amplitude reference tape has been estab- lished at NBS for the
43、 physical recording density of 9042 ftpi (356 ftpmm). Second- width, 0.19 inch f 0.02 inch (4.8 mm f 0.51 mm); thick- ness, 0.0008 inch (0.02 mm) maximum. (2) Tape is not attached to the hub. Figure 1 Usable Recording Area 9 AMERICAN NATIONAL STANDARD X3.157-1987 3.17 Total Character Skew. The devia
44、tion, during reading, from time coincidence (converted to apparent length) of the bits within a recorded character. 3.18 Character. A unit of information consisting of one byte plus a parity bit recorded as a unit. 3.19 Byte. A contiguous set of 8 bits that are acted on as a unit. 4. Recording 4.1 M
45、ethod. The recording method shall be phase en- coding, as described in 4.1.1 through 4.1.3. 4.1 .l A “ONE” data bit is defined as a flux transi- tion to the polarity (see 4.5.1) of the interblock gap, when reading in the forward direction. 4.1.2 A “ZERO” data bit is defined as flux transi- tion to t
46、he polarity opposite to that of the interblock gap, when reading in the forward direction. 4.1.3 A flux transition shall be written at the nomi- nal midpoint between successive “ONE” bits or be- tween successive “ZERO” bits, to establish proper polarity. This flux transition shall be called a phase
47、flux transition. 4.2 Density of Recording. The recording density shall be 3200 cpi (126 cpmm) nominal. The nominal charac- ter spacing, exclusive of phase flux transitions, shall be 312.5 microinches (7.94 micrometers), subject to the variations specified in 4.2.1 and 4.2.2. 4.2.1 Long-term average
48、(static) character spacing shall be within ?4% of nominal spacing. This average shall be measured over a minimum of 240 000 succes- sive characters. 4.2.2 Short-term (dynamic) character spacing, ex- cluding the effects of 4.3, shall be within +lO% of the long-term average character spacing. The shor
49、t-term character spacing shall change at a rate not to exceed 0.5% per character averaged over the three preceding characters. 4.3 Flux Transition Spacing. To determine the instan- taneous spacing between any two flux transitions, 4.3.1 and 4.3.2 shall be taken together. 4.3.1 Spacing 4.3.1 .l The spacing between successive data bits without an intervening phase flux transition shall be between 85% and 108% of the short-term character spacing. 4.3.1.2 The spacing between successive data bits with an intervening phase flux transition shall be be- tween 93% and 112% of the short-term
