Disclosure to Promote the Right To Information

Transcription

1 इ टरन ट म नक Disclosure Promote the Right To nformation Whereas the Parliament of ndia has set out provide a practical regime of right information for citizens secure access information under the control of public authorities, in order promote transparency and accountability in the working of every public authority, and whereas the attached publication of the Bureau of ndian Standards is of particular interest the public, particularly disadvantaged communities and those engaged in the pursuit of education and knowledge, the attached public safety standard is made available promote the timely dissemination of this information in an accurate manner the public. ज न1 क अ+धक र, ज 1 क अ+धक र Mazdoor Kisan Shakti Sangathan The Right nformation, The Right Live प0र 1 क छ ड न' 5 तरफ Jawaharlal Nehru Step Out From the Old the New S (1989): nformation Processing-Magnetic Tape Cassette and Cartridge Labelling and File Structure for nformation nterchange [LTD 16: Computer Hardware, Peripherals and dentification Cards]! न $ एक न' भ रत क +नम-ण Satyanarayan Gangaram Pitroda nvent a New ndia Using Knowledge! न एक ऐस खज न > ज कभ च0र य नहB ज सकत ह ह Bhartṛhari Nītiśatakam Knowledge is such a treasure which cannot be slen

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4 S12660:1989 S :1978 ndian Standard NFORMATON PROCESSNG-MAGNETC TAPE CASSETTE AN-D CARTRDGE LABELLNG AND FLE STRUCTURE FOR NFORMATON NTERCHANGE UDC BS 1990 BUREAU OF NDAN STANDARDS MANA! BHAVAN, 9 BAHADUR SHAH ZAFAR MARG NEW DELH December 1990 Price Group 7

5 ndian Standard S : 1969 S0 4341: 1976 NFORMATON PROCESSNG-MAGNETC TAPE CASS~El-TE AND CARTRDGE LABELLNG AN~D FLE STRlJCTtJRE FOR NFORMATON NTERCHANGE NATONAL FOREWORD This ~lndian Standard, which is identical with S : 1978 nformation processing-magnetic tape cassette and cartridge labelling and file structure for information interchange, issued by the nternational Organization for Standardization (SO), was adopted by the Bureau of ndian Standards on 6 February 1989 on the recommendation of the Computers, Business Machines and Calculars Sectional Committee (LTDC 24) and approval of the Electronic and Telecommunication Division Council. n the adopted standard certain terminology and conventions are not identical wiih those used in ndian Standards; attention is especially drawn the following: a) Wherever the words nternational Standard appear referring this standard, they should be read as ndian Standard. b) Comma (, 1 has been used as a decima~marker while in ndian Standards the current practice is use a point (. as the decimal marker. CROSS REFERENCES tn this ndian Standard, the following nternational Standards are referred. Read in their respective place the following: n terna tional Standard Corre2ponding ndian Standard Degree of Correspondence S0 646: bit coded character S : t bit coded character Technically equivalent se1 for information processing set for information interchange interchange S0 1001: l-979 nformation process- S : 1985 Magnetic tape dentical ing- Magnetic tape labelling and file labelling and file structures for structure for information interchange information processing The Computers, Business Machines and Calculars Sectional Committee has reviewed the provisions of following S0 Standards and has decided that these are acceptable for use in conjunction with this standard: S nformation processing-mplementation of the 7-bit coded character set and its 7-bit and 8-bit extensions on 3.81 mm magnetic tape cassette for data interchange S nformation processing-3.81 mm in) magnetic tape cassette for information interchange, 32 bpmm (800 bpi), phase encoded 3

6 As in the Original Standard, this Page is ntentionally Left Blank

7 S.12860: 1989 S : NTRODUCTON The aim of this nternational Standard is make possible the interchange of information recorded on magnetic tape cassettes and cartridges between different users and different data processing and data capture equipment. This is accomplished by the arrangement of magnetically recorded separars and labels, structure and identify the files. To provide for the wide range of equipment and applications using magnetic tape cassettes, three systems of increasing complexity are specified. t is possible distinguish between the three systems by reading the first block recorded on a particular volume. n order that a cassette which carries more sophisticated labelling may be copied on unsophisticated equipment, the terminating conditions for end of track and end of data within a cassette are identical in all three of these systems. Thus, support of the basic system is a necessary requirement ensure data interchangeability from simple data preparation devices more complex data processing systems. The third system is provided only for use in the most sophisticated environment, where S for magnetic tape labelling is already employed. Throughout the whole of this international Standard, the use of the 7-bit coded character set specified in S0 646 is implied. NOTE -Whenever the word cassette is used, the word cartridge is also implied. t is felt that the illustrations and examples given for cassettes can readily be interpreted cover similar situations for multi-track cartridges. 1 SCOPE AND FELD OF APPLCATOP This nternational Standard specifies fife structures for data interchange on magnetic tape cassettes. To provide for the range of sophistication in equipment and applications, three systemsare specified : a) the basic system, employing only hardwaredefined separars structure the files; b) the compact system, employing special data blocks with information content (labels), which are capable of being recorded using only numeric equipment; c) the extended system, employing the magnetic tam labelling system specified in S gether with n& labels, define a more comprehensive labelling system. This nternational Standard is not limited the 3,81 mm magnetic tape cassette described in S but could also be applied higher capacity cassettes or cartridges. 2 REFERENCES S0 646, 7-hit coded character set for information processing interchange. SO 100 1, lnforma tion processing - Magnetic rape labelling and file structure for information interchange. S0 3275, nformation processing - mplementation of the 7&t coded character set and its 7&t and B-bit extensions on 3,81 mm magnetic tiy3e cassette for data interchange. S0 3407, nformation processing mm (0.150 in) magnetic tape casserre for information interchange, 32 bpmm (800 bpi), phase encoded. 3

8 S : 1989 is : DEFNTONS For the purposes of this international Standard the following terms have the meanings indicated. NOTE - For a better explanation, the concepts have,where appropriate, been listed separately -as lagical and physical. The definition of a term that is used in an nternational Standard related this subject conforms its usage in that nternational Standard; the definition of a.term that is in common use in a context related this nternational Standard conforms that common usage. label : A block, at the beginning or at the end of a volume, of a track or of a file, that identifies, characterizes and/or delimits that volume, track or file. A label is not considered be part of a file. label identifier : One or more characters recorded in the label identify the label. characters used in a label : Only a subset of the char&ters of the 7-bit code defined in S0 646 is used in the label. The allowable characters are described in the following way : - n characters : any numeric character from 0 9. ile : A collection of infornation consisting ~of, ecords pertaining a ingle subject volume : A dismountable physical unit of srage media, for example a complete cassette con- Examples : n the context rf business data, a payroll - two tracks used ile, an invenry file. serially and sequentially for data inte< - The delineation of a change~as specified ile may be arbitrary. in S or - a characters : any numeric, alphabetic or special character of the centre four columns of th e code table except position 5/15 and those positions where there is provision for alternative graphic representation. tape mark : A delimiter used indicate the boundary between file data and labels, and also between certain labels. n the basic system it is used separate files. NOTES 1 The tape mark configuration is specified in the relevant nternational Standard for data interchange on magnetic tape cassettes. 2 Throughout this nternational Standard the tape mark is in- dicated as an asterisk( ). x-r J or part of a track or lolume, or on more than )ne volume. (number 1, side A) used serially for data interchange with the use of track number 2, side 6, defined by agreement between the interchange parties as specified in S / double tape mark : A delimiter consisting of two consecutive tape marks that is used indicate the end of a volume or.of a file set. NOTE - Except in the basic system, two consecutive tape marks also occur when an empty file section or an empty file exists on a uolume, in which case they are not interpreted as a double mark but rather as two single tape marks framing an empty file section. n this context empty means that no blocks are present between the tape mark following the header label and the tape mark preceding the end of volume, end of track or end of file label of that file section or file. - The sections of a file in a vokrme shall not have sections of other files interspersed. volume set : A collection ore related files, of one or more volumes 017 which one and only,one 4

9 S 12660:1969 S0 4241: BASC SYSTEM There are then two possibilities : 4.1 ntroduction The basic system permits the structuring of one or more files on one volume by means of hardware separars (tape marks) only. Each volume is independent; multivolume files are not provided. No magnetically recorded labels are used. The procedures for recording and detecting end of data on a track are defined in the relevant nternational Standards for media. 4.2 Use of tape marks Tape marks are used with the following significance indicate the structure of volumes and files f the file is not the last file of the set, the resulting configuration will be as illustrated in figure 2a) f the file is the last file of the set, the next track will be terminated by a third tape mark as illustrated in figure 2b), in this case the last two tape marks are be interpreted as an end of data indicar. a) Bin& file, on0 track pkq b) Single file, two tra& pzyp-1 Start of volume File separar ntermediate end of track ntermediate start of track End of data (and end of volume) *... c) Multi-file, one treck. FLE A FLE B * d) Multi-file, two tracks FLE A FLE B FLE B FLE C * t is not permitted for one file separar be immediately followed by another since this signifies end of data; thus, there can be no empty file sections as described in the definition of double tape mark in clause 3. Two tape marks not signifying end of data may occur when an intermediate start of track is immediately followed by a file separar : this condition is explained in 4.4 and Structuring the files FGURE 1 - Filestructure a) ntermediate start of track followed by file separar Multi-file, two tracks, coincident end of file and intermediate start of track - FLEA b) Coincidence of end of lest file end intermdiete atut of track Figure 1 illustrates the use of tape marks establish the file structure according the definitions of 4.2. n this figure and figure 2, the beginning of the tape is at the left and the end of the track is at the right. Each box represents a track. - FLE A FLE B tr ** FGURE 2 - File ttructure - Specie1 ceaes f the end-of-tape marker is encountered whilst a data block is being written, then, unless the system avoids the situation by, for example, erasing the current block, the system will complete writing the data block, and will then close the track with an intermediate end of track tape mark..the next track is opened with an intermediate start of track tape mark [as illustrated in figure 1 b) and d)], and the file is continued. 4.4 Coincidence of end of file and intermediate start of track This situation arises when the end-of-tape marker is recognized whilst the system is writing the last data block of the file. n this case the system will close the track and open the next track as indicated in 4.3, except that no data blocks of the completed file will be written in the next track, but only a file separar. 4.5 Coincidence of end of file and intermediate end of track This situation arises when the end-of-tape marker is recognized whilst the system is writingthe tape mark following a file. There are then two possibilities : f the file is not the last file of a set, the track is terminated at that point, so that the tape mark already written is now be interpreted as an intermediate end of track indicar. The next track starts with an intermediate start of track indicar, followed by a file separar indicar, as illustrated in figure 2a) f the file is the last file of a set, the system will write a second tape mark complete the track with an end of data indicar as illustrated in figures la) and 1~).

10 S : 1989 S : End of available space f the end-of-tape marker is recognized at the end of the last or only track on the volume which is available for recording, the file must be terminated with an end of data indicar as illustrated in figure Recording density 4.8 By-pass or check-point records Only the relevant data blocks shall be written on a cassette used for interchange. Since by-pass information and checkpoint records are considered be extraneous the interchange, and no standard means of -identification is provided, the recording of by-pass and check-point information is not allowed on cassettes for interchange. The blocks recorded on all volumes containing a file set shall be recorded with the same density. 6

11 S :-1999 S : COMPACT SYSTEM File Header Label (HDR) 5.1 ntroduction The compact system-permits the structuring of one or more files on one or more volumes by means of magnetically recorded labels and tape marks. The labels are capable of being recorded by equipment which uses only n characters but provision is made for the use of a characters in appropriate fields. The procedures for recording and detecting end of data on a track are defined in the relevant nternational Standards for media. ~5.2 Use of tape marks The tape mark is used separate labels from file.data and from other labels. 5.3 Formats and contents of labels A label is a 32character block, the character positions of which are numbered They are classified in fo ur types as given in the table. TABLE - Classifiiion of Wes Tw- N8lll8 Mnnnonk Mmtifii End of track 1 End of file or of last file section End of Track Label End of Volume End of File Label ETR 3 EOV 7 EOF 9 NOTE - ETR and EOV both imply end of first or intermediate fil le. :herecter position (CP) Field neme Fiti -& 1 Label dentifier 1 1 Content 2 Volume dentifier 4 a characters. Permanently as- 5 signed by the owner identify the volume 6 File dentifier 8 a -characters. As signed by the origin 13 ar identify the file 14 end File Section Number 2 n characters. dentifies the section among other sections of the file Creation Date Retention Period Block Count 5 Two n cheractars for the year followed by three n characters for the day ( ) within the yea 3 n characters. Specifies a number of days 4 Bw6 28 Label Standard 1 a character. n- Version dicates the version of this lnter&ona Standard Reserved for future standardization means this version End of Track Label (ETR) Cherecter Field porition Field neme (CP) - 1 Label dentifier Same as the corres ponding fields in 23 HDR Content 22 Same as the corresponding fields in HDR or 22 ZERO characters Block Count 4 n characters 7

12 S : f989 S : End of Volume Label (EOV) 5.43 File Section Number (HDR, CP 14 and 15) afield name The number of the first section of a file-is 01. This number is increased by 1 for each successive track or volume of the file. (_ 1 2. Label dentifier Same as the corras- 23 HDR ponding fields in Block Count 53.4 End of File Label (EOF) 12 -fiarnetthe co&- ponding fields in HDR or 22 ZERO characters n characters Retention Period (HDR, CP 21 23) The Retention Period is a quantity be added the Creation Date form the expiration date. The retention period may exceed one year. A file is regarded as expired on a day the date of which is equal or later than the expiration date. When this condition is satisfied, the remainder of the volume set may be overwritten. To be effective on multi-file volumes, therefore, the expiration date of a file must be less than or equal the expiration dates of all previous files on the volume set. i ,: 28 i Field name Field lrwjth Content Label dentifier Same as the corresponding fields in HDR 22 Same as the corresponding fields in HDR or 22 ZERO characters Block Count n characters Same as the corres- 5 Same as thecorresponding fields in HDR ponding fields in HDR or 5 ZERO characters Block Count (ETR, EOV, EOF, CP 24 27) The Block Count denotes only the number of data ~blocks since the preceding HDR label. This count excludes label blocks and tape mark blocks. f the Block Count has the value zero, it is ignored. This field is provided in order that when a magnetic tape cassette is read the system may ensure that no blocks have been skipped and no false blocks have been inserted. The particular error of equal numbers of skipped and false blocks may escape detection Label Standard Version (HDR, CP 28) 5.4 Processing of label fields General the Label dentifier must be written with the content as specified. Other fields may have the content as specified or a default value of the appropriate number of ZERO characters. On reading, the fields may be treated as desired. This will appear in every HDR, and must have the same value in every HDR in a voiume set. t specifies successive versions of this nternational Standard that may be defined, and for that purpose numeric values will be used, as far as possible. t is also useful distinguish between future standards and parochial practice that may develop in the meantime. Applications which record a value other than 1 in this field produce non-standard volumes. This may result in a subsequent failure of information interchange Use of data in label fields On input, the system may override data found in labels being processed by that system with new values of those data provided from other sources. The new values may be supplied before the file is processed (for example compiled values) or after the processing has begun (for example system control statement), at the option of the system implemenrs. 5.5 Structuring the files Labels and tape marks are used establish the file structure according the following rules and as illustrated in the accompanying figures 3 7. n these figures the beginning of the tape is at the left and the end of the tape is at the right. Labels are represented by their mnemonic identifiers. 8

13 S : 1999 CSO 4341 : Configurations of files within the tracks of a volume The various configurations of files that can be formed according these rules are illustrated in figure 3. Each box represents a track End of File Label _ The End of File Label shall follow the last data block of the file and be separated from the file by a tape mark. Single file, ens trade HDR FLE A EOF * Tape mark after End of File Label f the file ends within a volume, a tape mark shall immediately follow the End of File Label. _ Single file, two traclcs HDR FLE A ETR * HDR + FLE A EOF ** f the file is the last file of a file set, a double tape mark shall immediately follow the End of File Label. Multi-file, one track fndof Track Label HDR FLE A EOF * HDR FLE B EOF * Multi-file, two tracks HDR FLE A EOF HDR FLE 6 ETR f the file extends over the end of a track, the End of Track Label shall follow the last data block on that track and be separated from that data block by a tape mark. The End of Track Label shall always be followed by a single tape mark. HDR FLE B EOF HDR FLE C EOF * FGURE 3 -Single-volume file structure 552 Configurations of files in a multi-volume case The twoconfigurationsof files that can be formed according these rules are illustrated in figure 4. The distinction between tracks within the volumes is not shown, and the configurations within the volumes are as given in figure 3. Each box represents a volume. Single file, multi-volume End of Volume Label f the file extends over the end of a volume, the End of Volume Label shall follow the last data block on that track and be separated from that data block by a tape mark. The End of Volume Label shall always be followed by a double tape mark Empty file or file section When an empty file or file section is present, the rules stated in 5.5.4, 5.5.5, and will cause two consecutive tape marks be written between the File Header Label and the End of File, Track or Volume Label. HDR FLE A EOV * HDR * FLE A EOF * Multi-file, multi-volume HDR FLE A EOF HDR FLE B EOV * HDR FLE B EOF HDR * FLE C EOF Continuation file section in a multi-track or multivolume file The first data block of a continuation file section shall be preceded by a File Header Label as described in and This includes a copy of the last File Header Label on the previous track or volume, in which the File Section Number is increased by one and the Volume dentifier may be different. FGURE 4 -Multi-volume 5.53 File Header Label file structure Each file shall be preceded by the File Header Label Data File data shall follow the File Header Label and be separated from the label by a tape mark Coincidence of end of file and end-of-tape marker f the end of a file coincides with an intermediate end of track or the end of a volume, then, unless the system avoids the situation by, for example, erasing the current block, three situations are possible : The end-of-tape marker is detected whilst the system is writing the last data block of the file. n this case the system will complete writing the data block and close the track or volume as described in or respectively. The file is continued on the next track or volume

14 S : 198s S : 1978 by writing a File Header Label (see , two tape marks and an End of File Label. Examples are given in figures 5 and FLE A EOF HDR * EOV *.. FLE A * ETR HDR * EOF HDR * FLE B... FlGURb 5 - Empty file section at intermediate start of treck HDR * EOF HDR FLE B... FGURE 6 - Empty file section at start of continuetion volume The end-of-tape marker is recognized whilst the system is writing the End of File Label or the tape mark which precedes or follows it, and the file is not the last of a set. n this case the system will complete the writing of the End ~of File Label and the tape mark following it. The File Header Label of the next file will then be written followed by an empty file section, and the track or volume terminated by an End of Track or End of Volume Label respectively. The File Header Label will then be rewritten at the start of the next track or volume. Examples are given in figures 7 and 8. FGURE 8 - Empty file eection at end of volume The end-of-tape marker is recognized whilst the system is writing the End of File Label or the tape mark which precedes or follows it and the file is the last file of a set. n this case the system will complete the writing of the End of File Label and the tape mark following it and then close the volume with a second tape mark as described in Coincidence of beginning of ~file and endsf-tape marker f the end-of-tape marker is recognized whiht the system is writing the File Header Label or the tape mark following it, then the File Header Label will -be followed by an empty file section and the track or volume terminated by an End of Track or End of Volume Label respectively. The File Header Label will then be rewritten at the start of the next track or volume. The resulting configurations are illustrated in figures 7 and Recording density The blocks recorded on all volumes containing a file set shall be recorded with the same density. 5.7 By-pass or check-point records FGURE 7 - Empty file eection et intermediete endsf treck Only the relevant data blocks shall be written on a cassette used for interchange. Since by-pass information and checkpoint records are considered be extraneous the interchange, and no standard means of identification is provided, the recording of by-pass and check-point information is not allowed on cassettes for interchange. 10

15 is : 1999 S : 19l9 6 EXTENDED-SYSTEM Second End of Track Label (ETR2) (optional) 6.1 lntroductjon The exrended system provides the full range of facilities described in S gether with certain additional features control the transition from track track within the volume. The remainder of this clause specifies the format of the End of Track (ETR and ETR2) and Start of Track (STRl Labels and the file structure resutting from.their use. The procedures for recording and detecting end of data on a track are defined in the relevant nternational Standards for media. Character Field position Field name length (CP) Content 1 Label dentifier 3 ETR 3 4 Label Number Same as the corres- 76 Same as the corres ponding fields in ponding fields in 80 HDR2, as speci- HDRZ, as-specified in.so 1001 fied in S Use of tape marks Other optional labels (ETR3 9) The use of tape marks is the same as in S with the addition described in Formats and contents of labels First End of Track Label (ETRl) 4 Label Number ,6, 7,8 or 9 Character position (CP) Field namo Field length Content 5 Reserved for System Software 80 Use 76 a characters 1 Label dentifier 3 ETR 3 4 Label Number Same as the corres- 50 Same as the corres ponding fields in pondi,ng fields in 54 HDR 1 as speci- HDRi, as specified in S fied in S Block Count ~6 n chqracters. Denote: the num- 60 ber of data blocks since the preceding beginning of file label group. This count excludes labe blocks and tape mark blocks Same as the corresponding fields in HDR 1, as specified in S Same as the corresponding fields in HDR 1, as specified in S Srart of Track Label (STR 1) Character Field position Field name Content length CP) 1 Label dentifier 3 STR 3 4 Label Number Same as the corres- 7 Same as the corres ponding fields in ponding fields in 11 VOL, as speci- VOLl, as specified in S fied in S Track Number 1 n character 13 Same as the corres- 68 Same as the corres ponding fields in ponding fields in 80 VOLl, as speci- VOLl, as speci- fied in S fied in S /

16 S : 1989 S : Processing of label fields This sub-clause contains references only the fields of ETRl and STRl and those fields of other labels which are affected by the existence of track transitions File Section Number (HDRl, CP 28 31, also in ETRl, EOVl, EOFl) The number of the first section of a file is This number is increased by 1 for each successive track or volume of the file. 6.5 Structuring the files Labels and tape marks are used establish the file structure according the following rules and as illustrated in the accompanying figures n these figures the beginning of the tape is at the left, and the end of the tape is at the right. The figures show only the required labels in each label group Configurations of files within the tracks of a volume The various configurations of files that can be formed according these rules are illustrated in figure 9. Each box represents a track Track Number (STR 1, CP 12) Configurations of files in a multi-volume case The numbering of the tracks commences at 1. However, The two configurations of files that can be formed because the first STRl label appears on the second track according these rules are illustrated in figure 10. Each of the volume, the value of Track Number in that label is 2. box represents a volume. The distinction between tracks This value is incremented by 1 for each additional track is not shown. The configurations within the volume are as on the volume. in figure 9. Wgle file. one tr8ck ~ VOL HDRl * FLE A EOFl * c hglefile, two tracks VOL HDR FLE A ETRl STRl HDR FLE A EOFl * Jlulti-file, one track VOLl HDR FLE A EOFl HDRl FLE B EOFl * Hultl-fllr, two tracks VOLl HDR * FLE A EOFl * HDR FLE B ETR STRl HDRl * FLE B EOF HDRl FLE C * EOF ** FGURE 9 -Single-volume file structures Single file, multi-volume VOL HDR FLE A EOV * VOL HDR FLE A EOFl * Multi-file, multi-volume VOLl HDR FLE B EOFl HDRl FLE C EOF * FGURE 10 - Multi-volume file structures

17 S : 1989 S : End of Track Labels f the file extends over the end of a track, the End of Track Label (ETRl) shall follow the last data block on that track and be separated from that data block by a tape mark. f other end of track labels (ETR2 ETRS) are used, they shall immediately follow the ETRl label. The last label of an end of track label group shall always be followed by a tape mark. not the last file of a set. n this case the system will complete the writing of the end of file label group. The beginning of file label ~group of the next file will then be written followed by an empty file section, and the track will be terminated by an end of track label group. The beginning of file label group will then be rewritten at the start of the next track, following the STRl label. This is illustrated in figure ntermediate Start of Track Each track of the volume except the first shall commence with a Start of Track Label. This Label shall be immediately followed by the file header label group of the next file section, as specified in This label shall not appear at any other place on the track Continuation file section in a multi-track or multi- volume file The first data block of a continuation file section shall be preceded by a beginning of file label group. This includes an exact copy of the last beginning of file label group on the previous track or volume except that the file section number which is on HDRl is increased by 1 (see 6.4.1) Coincidence of end of file and end of track f the end of a file coincides with an end of track, then, unless the system avoids the situation, by, for example, erasing the current block, three situations are possible : The end-of-tape marker is recognized whilst the system is writing the last data block 6f the file. n this case the system will complete writing the data block and close the track as described in The file is continued on the next track or volume by writing a Start of Track Label or Volume Header Label, a file header label group (see 6.5.5). two tape marks and an end of file label group. An example of the first case is illustrated in figure 11. FGURE 12 - Empty file -ion at itttermditie end of trade The end-of-tape marker is recognized whilst the system is writing the end of file label group and the file is the last file of a set. n this case the system will complete the writing of the end of file label group and the tape mark following it and then close the track with a second tape mark Coincidence of beginning of file and end-of-tape marker f the end-of-tape marker is recognized whilst the system is writing the beginning of file label group, then this group will be followed by an empty file section and the track will be terminated by an end of track label group. The beginning of file label group will then be rewritten at the start of the next track following the STRl label. This is illustrated in figure Use of optional labels The use of any optional label at the end-of-track condition may result in such labels being written past the usable recording area. 6.7 Recording density The blocks recorded on all volumes con&ining a file set shall be recorded with the same density.. FLE A ETRl STRl HDRl * EOF!..,:3Rl FLE B.. FGURE 11 - Empty file section at intermediate start oftrack The end-of-tape marker is recognized whilst the system is writing the end of file label group and the file is 6.8 By-pass or-check-point records Only the relevant data blocks shall be written on a cassette used for interchange. Since by-pass information and checkpoint records are considered be extrineous the interchange, and no standard means of identification is-provided, the recording of by-pass and check-point information is not allowed on cassettes for interchange. 13

18 Bureau of ndian Standards BS is a statury institution established under the Bureau of /n&an Standards Act, 1986 promote harmonious development of the activities of standardization, marking and quality certification of goods and attending connected matters in the country. Copyright BS has the copyright of all its publications. No part of these publications may be reproduced in any form without the prior permission in writing of BS. This does not preclude the free use, in the course of implementing the standard, of necessary details, such as symbols and sizes, type or grade designations. Enquiries relating copyright be addressed the Direcr (Publications), BS. Revision of ndian Standards ndian Standards are reviewed periodically and revised, when necessary and amendments, if any, are issued from time time. Users of fndian Standards should ascertain that they are in possession of the latest amendments or edition. Comments on this ndian Standard may be sent BS giving the following reference: Dot : No. LTD 24 ( 1291 ) Amendments ssued Since Publication Amend No. Date of ssue Text Affected Headquarters : BUREAU OF N,DAN STANDARDS Manak Bhavan, 9 Bahadur Shah Zafar Marg, New Delhi Telephones : , Telegrams : Manaksanstha ( Common all Offices ) Regional Offices : Central : Manak Bhavan, 9 Bahadur Shah Zafar Marg NEW DELH Eastern : l/14 C.. T. Scheme V M, V.. P. Road, Manikla CALCUTTA Northern : SC , Secr 35-C, CHANDGARH Southern : C.. T. Campus, V Cross Road, MADRAS Western : Manakalaya, E9 MDC, Marol, Andheri ( East ) BOMBAY Telephone : Branches : AHMADABAD. BANGALORE. BHOPAL. BHUBANESHWAR. COMBATORE. FARDABAD. GHAZABAD. GUWAHAT. HYDERABAD. 3APUR. KANPUR. PATNA. TRVANDRUM. Printed at Simco Printinu Press, Delhi. ndia