ISO-4341-1978.pdf
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1、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 lab
2、elling 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
3、 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
4、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 Licen
5、see=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
6、 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 c
7、ontext 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
8、- 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 del
9、ineation 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, defi
10、ned 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 col
11、lection 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
12、 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
13、 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 ma
14、rk : 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
15、 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 wh
16、en 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 t
17、ape 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
18、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
19、 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 ill
20、ustrated 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 f
21、ile, 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 - Inte
22、rmediate 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 definitio
23、n 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
24、 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 th
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