ISO-4341-1978.pdf

INTERNATIONAL STANDARD INTERNATIONAL ORGANIZATION FOR STANDARDIZATIONWEXJYHAPOHAR OPAHH3Ai 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 tape labelling system specified in IS0 1001 together with new labels, to define a more comprehensive labelling system. This International Standard is not limited to the 3,81 mm magnetic tape cassette described in IS0 3407 but could also be applied to higher capacity cassettes or cartridges. 2 REFERENCES IS0 646, 7-bit coded character set for information pro- cessing interchange. I SO 1001, Information processing - Magnetic tape labelling and file structure for information interchange. ISO 3275, Information processing - Implementation of the 7-bit coded character set and its 7-bit and 8-bit extensions on 3.8 1 mm magnetic tape cassette for data interchange. IS0 3407, information processing - 3,81 mm (0.150 in) magnetic tape cassette for information interchange, 32 bpmm (800 bpi), phase encoded. 1 Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/22/2007 21:35:13 MDTNo reproduction or networking permitted without license from IHS -,-,- IS0 4341-1978 (E) 3 DEFINITIONS For the purposes of this International Standard the following terms have the meanings indicated. NOTE - For a better explanation, the concepts have, where appro- priate, been listed separately as logical and physical. The definition of a term that is used in an International Standard related to this subject conforms to its usage in that International Standard; the definition of a term that is in common use in a context related to this International Standard conforms to that common usage. Logical record : Related data treated as a unit of information. Physical block : A group of con- tiguously recorded charac- ters written or read as a unit, and terminated with an interblock gap. file : A collection of infor- volume : A dismountable mation consisting of physical unit of storage records pertaining to a media, for example a single subject complete cassette con- Examples : In the context sisting of either of business data, a payroll - two tracks used file, an inventory file. serially and sequen- - The delineation of a tially for data inter- file may be arbitrary. change as specified in IS0 3407 or - A file may be recorded on all or part of a track or volume, or on more than one volume. - a single track (number 1, side A) used serially for data interchange with the use of track number 2, side B, defined by agree- ment between the inter- change parties as spe- cified in IS0 3407 File section : That part of 3 file that is recorded on a single track of a cassette. - The sections of a file in a volume shall not have sections of other files interspersed. file set : A collection of volume set : A collection one or more related files, of one or more volumes on recorded consecutively which one and only one on a volume set. file set is recorded. 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 to be part of a file. label identifier : One or more characters recorded in the label to identify the label. characters used in a label : Only a subset of the characters of the 7-bit code defined in IS0 646 is used in the label. The allowable characters are described in the following way : - “n” characters : any numeric character from 0 to 9. - “a” characters : any numeric, alphabetic or special character of the centre four columns of the code table except position 5/15 and those positions where there is provision for alternative graphic representation. tape mark : A delimiter used to indicate the boundary between file data and labels, and also between certain labels. In the basic system it is used to separate files. NOTES 1 The tape mark configuration is specified in the relevant Inter- national Standard for data interchange on magnetic tape cassettes. 2 Throughout this International Standard the tape mark is in- dicated as an asterisk(*). double tape mark : A delimiter consisting of two conse- cutive tape marks that is used to 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 volume, in which case they are not interpreted as a double mark but rather as two single tape marks framing an empn/ file section. In 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. Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/22/2007 21:35:13 MDTNo reproduction or networking permitted without license from IHS -,-,- IS0 4341-1978 (E) 4 BASIC SYSTEM There are then two possibilities : 4.1 Introduction 4.4.1 If the file is not the last file of the set, the resulting configuration will be as illustrated in figure 2a). The basic system permits the structuring of one or more files on one volume by means of hardware separators (tape marks) only. Each volume is independent; multi- volume files are not provided. No magnetically recorded labels are used. 4.4.2 If 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 to be interpreted as an end of data indicator. The procedures for recording and detecting end of data on a track are defined in the relevant International Standards for media. a) Single file, one track 4.2 Use of tape marks b) Single file, two tracks Tape marks are used with the following significance to in- dicate the structure of volumes and files. I* I FILE A l * - Start of volume * . . . c) Multi-file, one track - File separator * . . . l FILE A l FILE B l * - Intermediate end of track * . . . d) Multi-file, two tracks - Intermediate start of track * . . . - End of data (and end of volume) * . . . I*FlLEA*FlLEBI I* FILE B l FILE C l * 1 It is not permitted for one file separator to 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. FIGURE 1 - File structure Two tape marks not signifying end of data may occur when an intermediate start of track is immediately followed by a file separator : this condition is explained in 4.4 and 4.5. I a) Intermediate start of treck followed by file separator Multi-file, two tracks, coincident end of file and intermediate start of track 4.3 Structuring the files pTYLETq I b) Coincidence of end of last file and intermediate start of track Figure 1 illustrates the use of tape marks to establish the file structure according to the definitions of 4.2. In 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. l FILE A * FILE B l ICI l * l FIGURE 2 - File structure - Special cases If 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 lb) and Id), and the file is continued. 4.5 Coincidence of end of file and intermediate end of track This situation arises when the end-of-tape marker is re- cognized whilst the system is writing the tape mark follow- ing a file. There are then two possibilities : 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. In 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 separator. 4.5.1 If 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 to be interpreted as an intermediate end of track indicator. The next track starts with an inter- mediate start of track indicator, followed by a file separ- ator indicator, as illustrated in figure 2a). 4.5.2 If the file is the fast file of a set, the system will write a second tape mark to complete the track with an end of data indicator as illustrated in figures la) and lc). 3 Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/22/2007 21:35:13 MDTNo reproduction or networking permitted without license from IHS -,-,- IS0 4341-1978 (E) 4.6 End of available space If 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 indicator as illustrated in figure 1. 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 check- point records are considered to be extraneous to the inter- change, and no standard means of identification is provided, the recording of by-pass and check-point information is not 4.7 Recording density The blocks recorded on all volumes containing a file set shall be recorded with the same density. allowed on cassettes for interchange. 4 Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/22/2007 21:35:13 MDTNo reproduction or networking permitted without license from IHS -,-,- 5 COMPACT SYSTEM 5.3.1 File Header Label (HDR) IS0 4341-1978 (E) 5.1 Introduction 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” charac- ters 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 International Standards for media. 5.2 Use of tape marks The tape mark is used to 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 1 to 32. They are classified into four types as given in the table. TABLE - Classification of labels I Type Name Mnemonic Identifier End of track End of Track Label ETR 3 End of Volume End of volume Labe, EOV 7 End of file or of last file End of File Label EOF 9 section NOTE - ETR and EOV both implv end of first or intermediate file section. Character position (CP) Field name Field length Content 1 Label Identifier 1 1 2 Volume Identifier 4 “a” characters. to Permanently as- 5 signed by the owne to identify the volume 6 File Identifier 8 “a” characters. As- to signed by the origir 13 ator to identify the file 14 and 15 File Section Number 2 “n” characters. Identifies the sec- tion among other sections of the file 16 to 20 Creation Date 5 Two “n” charac- ters for the year followed by three “n” characters for the day (001 to 366) within the ye: 21 Retention Period 3 “n” characters. to Specifies a number 23 of days 24 Block Count 4 0000 to 27 28 Label Standard Version 1 “a” character. In- dicates the version of this Internations Standard. 1 means this ver- sion. 29 to 32 Reserved for future 4 0000 standardization 5.3.2 End of Track Label (ETR) Character position (CP) Field name Field length Content I 1 I Label Identifier I 1 13 2 Same as the corres- 22 Same as the corres- to ponding fields in ponding fields in 23 HDR HDR or 22 ZERO I characters 24 Block Count 4 “n” characters to 27 28 Same as the corres- to ponding fields in 32 HDR 5 Same as the corres- ponding fields in HDR or 5 ZERO characters Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/22/2007 21:35:13 MDTNo reproduction or networking permitted without license from IHS -,-,- ISO4341-1978 (E) 5.3.3 End of Volume Label (EOV) 2 to 23 24 to 27 Block Count 28 Same as the corres- to ponding fields in 32 HDR 5 Same as the corres- ponding fields in HDR or 5 ZERO characters 5.3.4 End of File Label (EOF) Character position (CP) Field name 1 1 Label Identifier 1 19 2 Same as the corres- to ponding fields in 23 HDR 24 to 27 Block Count 4 “n” characters 28 Same as the corres- to ponding fields in 32 HDR Field length Content 22 Same as the corres- ponding fields in HDR or 22 ZERO characters 5 Same as the corres- ponding fields in HDR or 5 ZERO characters 5.4.3 File Section Number (H D R, CP 14 and 15) 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. 5.4.4 Retention Period (HDR, CP 21 to 23) The Retention Period is a quantity to be added to the Creation Date to 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 to 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, there- fore, the expiration date of a file must be less than or equal to the expiration dates of all previous files on the volume set. 5.4.5 Block Count (ETR, EOV, EOF, CP 24 to 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. If 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. 5.4 Processing of label fields 5.4.1 General The Label Identifier 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 charac- ters. On reading, the