EN 29293:1989

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Information processing - Volume and file structure of flexible disk cartridges for information interchange (ISO 9293:1987)Informationsverarbeitung - Kennsätze und Dateianordnung auf Diskette für den Datenaustausch (ISO 9293:1987, Ausg. 1)Traitement de l'information - Volume et structure des fichiers des cartouches a disquette pour l'échange d'information (ISO 9293:1987, éd. 1)Information processing - Volume and file structure of flexible disk cartridges for information interchange (ISO 9293:1987, ed. 1)35.220.21Magnetni diskiMagnetic disksICS:Ta slovenski standard je istoveten z:EN 29293:1989SIST EN 29293:1997en01-december-1997SIST EN 29293:1997SLOVENSKI
STANDARD
INTERNATIONAL STANDARD INTERNATIONAL ORGANIZATION FOR STANDARDIZATION ORGANISATION INTERNATIONALE DE NORMALISATION MEXAYHAPOAHAR OPTAHM3ALWlR no CTAHAAPTM3AL(MM Information processing - Volume and file structure of flexible disk cartridges for information interchange Traitement de i'information - Volume et structure des fichiers des cartouches à disquette pour i'échange d'information :so ,293 'irst edition 987-04-15 Reference number 170 9293 : 1987 (E) &! SIST EN 29293:1997

Foreword IS0 (the International Organization for Standardization) is a worldwide federation of national standards bodies (IS0 member bodies). The work of preparing International Standards is normally carried out through IS0 technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, govern- mental and non-governmental, in liaison with ISO, also take part in the work. Draft International Standards adopted by the technical committees are circulated to the member bodies for approval before their acceptance as International Standards by the IS0 Council. They are approved in accordance with IS0 procedures requiring at least 75 % approval by the member bodies voting. International Standard IS0 9293 was prepared by the European Computer Manufac- turers Association (as Standard ECMA-107) and was adopted, under a special "fast- track" procedure, by Technical Committee ISO/TC 97, Information processing systems, in parallel with its approval by the IS0 member bodies. ' Users should note that all International Standards undergo revision from time to time and that any reference made herein to any other International Standard implies its latest edition, unless otherwise stated. O International Organization for Standardization, 1991 0 Printed in Switzerland SIST EN 29293:1997

Contents Section one : General IS0 9293 : 1987 (E) Page . O Introduction 1 Scope and field of application . 2 Conformance . 2.1 2.2 Conformance of a flexible disk cartridge . Conformance of an information processing system . . 3 References . 4 Definitions 4.1 byte . 4.2 4.3 data interchange standard . 4.4 defective sector 4.5 descriptor . 4.6 file . 4.7 formatting . 4.8 implementation . 4.9 initialization . 4.10 originating system . 4.11 receiving system . data field of a sector . . 4.12 sector . 4.13 track 4.14 user . 4.15 fixed-length record . 4.16 record . 4.17 segment . 4.18 segmented record . 4.19 variable-length record . . . 5 Notations 5.1 Decimal and hexadecimal notations . 5.2 Other notations . 5.3 Capital letters . Section two : Requirements for the medium . 6 Volume structure 6.1 Arrangement of data on a flexible disk cartridge . 6.1.1 FDC parameters . 6.1.2 Physical Addresses . 6.1.3 Logical Sector Number . 6.1.4 System Area and Data Area . 6.1.5 Parameters of the Volume Structure . Arrangement of the Data Area . 6.2.1 Clusters . 6.2.2 Status of clusters . Arrangement of the System Area . 6.3.1 FDC Descriptor and space for system use . 6.3.2 File Allocation Table (FAT) . 6.3.3 Root Directory . 6.3.4 Size of the System Area . 6.4 Files . 6.4.1 File Space . 6.4.2 Relation to clusters . 6.4.3 File length . 6.2 6.3 . 6.5 Sub-directories . 7 Contents of a file 1 1 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 4 4 4 4 4 5 5 5 5 5 5 5 5 5 6 6 iii SIST EN 29293:1997

IS0 9293 : 1987 (E) Page 8 Recording of descriptor fields . 6 8.1 Numerical values in one-byte fields . 6 8.2 Numerical values in two-byte fields . 6 8.3 Numerical values in four-byte fields . 6 8.4 Pairs of 12-bit integers . 6 8.5 Character set and coding . 6 8.6 Justification of characters . 7 9 FDCDescriptor . 7 9.1 FDC Descriptor layout . 7 9.2 FDC Descriptor fields . 7 9.2.1 7 9.2.2 Creating System Identifier (BP 4 to 11) . 7 9.2.3 Sector Size (BP 12and 13) . 7 9.2.4 Sectors per Cluster (BP 14) . 7 9.2.5 Reserved Sector Count (BP 15and 16) . 7 9.2.6 Number of FATS (BP 17) . 7 9.2.7 Root Directory Entries (BP 18 and 19) . 7 9.2.8 Total Sectors (BP20and21) . 7 9.2.9 Medium Identifier (BP22) . 7 9.2.10 Sectors per FAT (BP23 and 24) . 7 9.2.11 Sectors per Track (BP 25 and 26) . 8 9.2.12 Number of Sides (BP 27 and 28) . 8 9.2.13 Field reserved for future standardization (BP 29 and 30) . 8 9.2.14 Field reserved for system use (BP 31 to 512) . 8 10 File Allocation Table . 8 10.1 Format Identifier . 8 10.2 FATenties . 8 10.2.1 FATentrysize . 8 10.2.2 Number of FAT entries . 8 10.2.3 FAT entry values . 8 10.2.4 Maximum Cluster Number (MAX) . 8 10.3 Number of sectors in each FAT . 8 10.4 Recorded form of the FAT . 9 11 File directories . 9 11.1 Characteristics . 9 11.2 Directoryentry types . 9 11.3 General definition of Directory Entry Fields . 9 11.3.1 Name(BP1 to81 . 9 11.3.2 NameExtension(BP9to11) . 9 11.3.3 Attributes (BP 12) . 9 11.3.4 Reserved Field (BP 13to22) . 10 11.3.5 Time Recorded (BP23and 24) . 10 Field reserved for system use (BP 1 to 3) . 11.3.6 Date Recorded (BP25and26) . 11.3.7 Starting Cluster Number (BP27and28) . 11.3.8 File Length (BP 29 to 32) . File Entry . 11.4.1 Name (BP 1 to8) . 11.4.2 Name Extension (BP9 to 11) . 11.4.3 Attributes (BP 12) . 11.4.4 Reserved Field (BP 13 to22) . 11.4.5 Time Recorded (BP23and24) . 11.4.6 Date Recorded (BP 25 and 26) . 11.4.7 Starting Cluster Number (BP 27and 28) . 11.4.8 File Length (BP29to32) . Volume Label Entry . 11.5.1 Nameand Name Extension (BP 1 to 11) . 11.5.2 Attributes (BP 12) . 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 SIST EN 29293:1997

..I * IS0 9293 : 1987 (E) Page 11.5.3 Reserved Field (BP 13 to22) ............................. 11.5.4 Tirne Recorded (BP23and24) ........................... 11.5.5 Date Recorded (BP25and 26) ............................ 11.5.6 Starting Cluster Number (BP 27 and 28) ................... 11.5.7 File Length (BP 29 to 32) ................................ 11.6 Sub-directory Pointer Entry ..................................... 11.6.1 Name(BP1 to8) ....................................... 11.6.2 NameExtension(BP9toll) ............................. 11.6.3 Attributes (BP 12) ...................................... 11.6.4 Reservedfield (BP 13to22) .............................. 11.6.5 Time Recorded (BP 23 and 24) ........................... 11.6.6 Date Recorded (BP25and26) ............................ 11.6.7 Starting Cluster Number (BP 27 and 28) ................... 11.6.8 File Length (BP29to32) ................................ 11.7 Sub-directory Identifier Entry .................................... 11.7.1 Name(BP1 to8) ....................................... 11.7.2 Name Extension (BP9 to 11) ............................. 11.7.3 Attributes (BP 12) ...................................... 11.7.4 Reserved Field (BP 13 to 22) ............................. 11.7.5 TimeRecorded(BP23and24) ........................... 11.7.6 Date Recorded (BP25and 26) ............................ 11.7.7 Starting Cluster Number (BP 27 and 28) ................... 11.7.8 File Length (BP29to32) ................................ Sub-directory Parent Pointer entry ............................... 11.8.1 Name(BP1 to81 ....................................... 11.8.2 NameExtension(BP9toll) ............................. 11.8.3 Attributes (BP 12) ...................................... 11.8.4 Reserved Field (BP 13 to221 ............................. 11.8.5 Time Recorded (BP 23 and 24) ........................... 11.8.6 Date Recorded (BP25and 26) ............................ 11.8.7 Starting Cluster Number (BP27and 28) ................... 11.8.8 FileLength(BP29to32) ................................ 11.9 Not-currently-used Entry ....................................... 11.9.1 Name Field (BP 1 to 18) ................................. 11.9.2 Remaining bytes (BP9 to32) ............................ 11.10 Never-used Entry ............................................. 11.10.1 NameField(BP1 to81 ................................. 11.10.2 Remaining bytes (BP 9 to 32) ........................... 11.8 10 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 Section three: Requirements for systems 12 Requirements for the description of systems ............................ 13 13 Requirementsfor an originating system ................................. 13 13.3 Descriptors ................................................... 13 ...................................................... ......................................................... 13.1 General 13 13.2 Files 13 14 Requirements for a receiving system ................................... 13 14.3 Descriptors ................................................... 13 ...................................................... ......................................................... 14.1 General 13 14.2 Files 13 Section four: Record structure .................................................... 15 Record structure 14 15.1 General ...................................................... 14 15.2 Records 14 ...................................................... 15.2.1 Characteristics ......................................... 14 15.2.2 Measured Data Units ................................... 14 15.2.3 Fixed-length records .................................... 14 V SIST EN 29293:1997

IS0 9293 : 1987 (E) Page 15.2.4 Variable-length records . 14 15.2.5 Segmented records . 14 15.3 Attributes of record-structured files . 15 15.4 Requirements for systems implementing section four . 15 15.4.1 Originating systems . 15 15.4.2 Receiving systems . 15 Annexes A . Parameter values for FDCs conforming to an International Standard for data interchange . 16 B . Parameter values for other EDC formats . 17 C . IS0 646: International Reference Version (IRV) . 18 D . Example of volume structures and file location . 20 E . Index of acronyms . 23 vi SIST EN 29293:1997

__ ~~ INTERNATIONAL STANDARD IS0 9293 : 1987 (E) Information processing - Volume and file structure of flexible disk cartridges for information interchange Section one : General O Introduction For many purposes IS0 7665 provides a satisfactory data inter- change between different types of information-processing systems. However, it imposes some restrictions on the opera- tion of a system as follows : a) Each individual file must be recorded on the disk in a se- quential, "batch-processing" mode. After a set of files has been recorded on the disk, a file cannot be extended beyond its pre-determined length. It is common practice in small systems for the user to inter- act continuously with the system to update files. Files having a suitable structure for this purpose are not within the provision of IS0 7665. The interchange cartridge has to be created by an "export" copy process from the application's files, after the applica- tion has terminated. A similar "import" process is required in the receiving system. b) Limitations on the number of file labels permitted on an interchange FDC prevents the full use of the disk space if the average size of files is significantly less than, say 20 kbytes. For conventional data processing purposes this is usually satisfactory. However, the file sizes typically en- countered in text processing and small single-user systems are very much smaller and would lead to very inefficient use of the disk space. In view of these requirements it was decided to develop a second standard for volume and file structure of flexible disk cartridges, the provisions of which were to be based on already existing practice in general use world-wide. Hence this Inter- national Standard has the following beneficial characteristics, in addition to those of IS0 7665. - The interchange file will be especially for direct updating by interactive application. - There will be no limit on the number of individual files on an FDC, within the overall limitation of available space for holding files. Any file can be extended whenever required. These characteristics are advantageous for : - interchange of sets of text files or of small files, or of multiple-part document files; - interchange of any file when sender and recipient wish to carry out frequent update of the file between interchange cycles, for example files of commercial transactions. 1 Scope and field of application This International Standard specifies the volume and file struc- ture of flexible disk cartridges (FDC) for the interchange of information between users of information processing systems. It also specifies an optional record structure. This International Standard is applicable to various types of flexible disk cartridges including those identified in clause 3, and other types which may be the subject of future Inter- national Standards. This International Standard specifies the location of files of in- formation on a flexible disk cartridge, and also specifies a set of recorded descriptors which identifies : - the files which may be interchanged; - the locations of the files: - the attributes of the files; - the location of unused space for recording on the FDC; - the location of defective recording space on the FDC; - the attributes of the FDC and of the descriptors recorded on it. This International Standard also specifies requirements for the processes which are provided within information processing systems to enable information to be interchanged between dif- ferent systems, utilizing recorded flexible disk cartridges as the medium of interchange. For this purpose it specifies the func- tions within systems which are intended to originate or to receive flexible disk cartridges which conform to this Inter- national Standard. This International Standard provides a method for the alloca- tion of space that is independent of the number of files that are recorded on the volume, It also enables the sizes of the record- ed files to be expanded or contracted during processing, sub- ject only to the availability of unused recording space when needed. 1 SIST EN 29293:1997

IS0 9293 : 1987 (E) The contents and organization of the files are not specified by this International Standard and are subject to agreement be- tween the originator and the recipient of the interchanged FDC. 2 Conformance 2.1 Conformance of a flexible disk cartridge A flexible disk cartridge shall be in conformance with this Inter- national Standard when all information recorded on it conforms to the requirements of section 2 of this International Standard. A prerequisite to such conformance is the conformance of the flexible disk cartridge to the appropriate International Standard for data interchange of flexible disk cartridges. 2.2 Conformance of an information processing system An information processing system shall be in conformance with this International Standard if it meets the set of requirements specified in section 3 of this International Standard either for an originating system, or for a receiving system, or for both types of system. A statement of conformance shall identify which of these sets of requirements is met by the system. Conformance with this lnternation Standard does not require conformance with section 4. 3 References IS0 646, Information processing - IS0 7-bit coded character set for information interchange. IS0 7487, Information processing - Data interchange on 130 mm (5.25 in) flexible disk cartridges using modified fre- quency modulation recording at 7 958 ftprad, 1,9 tpmm (48 tpi), on both sides - Part 7: Dimensional, physical and magnetic character- istics. - Part 3: Track format B. IS0 7665, Information processing - File structure andlabelling of flexible disk cartridges for information interchange. IS0 8378, Information processing - Data interchange on 130 mm (5.25 in) flexible disk cartridges using modified fre- quency modulation recording at 7 958 ftprad, 3,8 tpmm (96 tpi), on both sides - Part I: Dimensional, physical and magnetic character- istics. - Part 3: Track format B. IS0 8630, Information processing - Data interchange on 130 mm (5.25 in) high density flexible cartridges using modified frequency modulation recording at 13 262 ftprad, 3,8 tpmm (96 tpi), on both sides - Part 7: Dimensional, physical and magnetic character- istics. 1 ) - Part 3: Track format B for 80 tracks. 1) IS0 8860, Information processing - Data interchange on 90 mm (3.5 in) flexible disk cartridges using modified frequency modulation recording at 7 958 ftprad, 5,3 tpmm (135 tpi), on both sides - Part 7: Dimensional, physical and magnetic character- istics. - Part 2: Track format. 4 Definitions For the purposes of this International Standard the following definitions apply. 4.1 byte: A string of binary digits operated upon as a unit. In this International Standard this term designates an 8-bit byte. 4.2 the data of a sector. data field of a sector: A fixed-length field containing 4.3 data interchange standard : A standard which defines the physical and magnetic characteristics, the recording method, and the track format of a flexible disk cartridge. 4.4 written without error. defective sector: A sector which cannot be read or 4.5 descriptor : A recorded structure containing descriptive information about the volume or a file. 4.6 file: A named collection of information. 4.7 formatting : Writing the control information establishing the physical addresses of sectors on the surfaces of a flexible disk cartridge. 4.8 implementation: A set of processes which enable an information processing system to behave as an originating system, or as a receiving system, or as both types of system. 4.9 initialization : Writing descriptors initially required to be on the FDC, prior to the commencement of general processing or use. 4.10 originating system : An information processing system which can record files on an FDC for the purpose of data interchange with another system. 1) At present at the stage of draft. 2 SIST EN 29293:1997

IS0 9293 : 1987 (E) 4.11 receiving system : An information processing system which can read files from an FDC which has been recorded by another system for the purpose of data interchange. 4.12 sector: That part of a track on a flexible disk cartridge that can be accessed independently of other parts of the track by the magnetic heads of the flexible disk drive. 4.13 track : That part of a flexible disk that can be accessed by a single magnetic head that is stationary while the disk makes a complete revolution. 4.14 user: A person or other entity (for example an applica- tion program) that causes the invocation of the services provid- ed by an implementation. In addition the following definitions apply specifically to section four. 4.15 which all records must have the same length. fixed-length record: A record contained in a file in 4.16 record : Related data treated as a unit of information. 4117 segment : A part of a record. 4.18 segmented record: A record contained in a file in which the records may have different lengths and each record may consist of one or more separate segments. 4.19 variable-length record : A record contained in a file in which the records may have different lengths but a record must not consist of separate segments. 5 Notation4 I this International Standard. 5.1 Decimal and hexadecimal notations Numbers in decimal notation are represented by decimal digits, namely O to 9. Numbers in hexadecimal notation are represented by hexa- decimal digits, namely O to 9 and A to F, shown in parentheses. 5.2 Other notations BP : Byte position within a Descriptor, starting with 1 ZERO : A single bit with the value O ONE: A single bit with the value 1 ip (x) : The integer part of x ceil(x) : The smallest integer that is not less than x rem(x,y) : The remainder of the integer division of x by y, that is, rem(x,y) = x - y x ip(xJy) 5.3 Capital letters Where a word or a group of words is used to designate a specific concept, for example the name of a descriptor field, it is printed with initial capital letters except for prepositions. Section two : Requirements for the medium 6 Volume structure 6.1 Arrangement of data on a flexible disk cartridge 6.1.1 FDC parameters For the purpose of this International Standard the significant parameters of the data interchange standard are shown in table 1. Table 1 FDC parameters Acronym Number of Recordable Sides Number of Tracks per Side Number of Sectors per Track Total Number of Sectors of the FDC Number of Bytes per Data Field of a Sector The values of these parameters shall be obtained from the text of an appropriate data interchange standard (see annex A), 6.1.2 Physical Addresses Each sector shall be identified by a Physical Address compris- ing the Side Number, the Track Number, and the Sector Number. The sides shall be numbered O and 1, tracks shall be numbered starting with 00, and the sectors shall be numbered starting with 1 on each track. / 6.1.3 Logical Sector Number Each sector on a volume shall be identified by a Logical Sector Number. There shall be a one-to-one correspondence between Physical Address and Logical Sector Number. The Logical Sector Numbers shall be assigned in an ascending sequence, beginning with O, starting at sector 1, track 00, side O, continu- ing onto track 00, side 1 (if the FDC is recordable on both sides) and then to track 01, side O, etc. The relation between the Side Number (“1, Track Number (TN), Sector Number (SN) and the Logical Sector Number (LSN) shall be given by the formulae: / LSN = SPT x [HN + (NOS x TN)I + SN - 1 3 SIST EN 29293:1997

IS0 9293 : 1987 (E) SN = rem (rem [LSN, (SPT x NOS)], SPT} + 1 {rem [LSN,(SPT x NOS11 S PT HN = ip 6.1.4 System Area and Data Area The space on an FDC shall be divided into a System Area and a Data Area. The System Area shall be recorded on track 00, side O and track 00. side 1. The System Area shall occupy sectors with the Logical Sector Numbers O to SSA - 1, where SSA is the number of sectors in the System Area (see 6.3.4). The System Area shall contain Descriptors which specify the recording format of the FDC, describe the use of the Data Area, and provide a Directory of the files on the volume. No part of any file shall be contained in the System Area. The Data Area shall occupy sectors with Logical Sector Numbers starting with SSA. Interchange files and supplemen- tary Descriptors (such as Sub-directories) shall be contained in the Data Area. Files not intended for interchange may $so be contained in the Data Area. 6.1.5 Parameters of the Volume Structure This International Standard specifies various types of data structure within the System Area and Data Area. The sizes of these data structures are identified by a set of numerical parameters. These parameters are listed in table 2. Table 2 I Parameter I Acronym Sectors per Cluster Reserved Sector Count Sectors per FAT Root Directory Entries sc RSC SF RDE The values of these parameters for each FDC type are contain- ed in annex A. 6.2 Arrangement of the Data Area 6.2.1 Clusters The Data Area shall be organized into units of allocation called clusters. Each cluster shall consist of the same number of sectors which shall be a power of 2, i.e. 1, 2, 4, 8, . . The number of sectors in each cluster (Sectors per Cluster, SC) shall be as specified in annex A. The data of a cluster shall be recorded in the Data Fields of its constituent sectors. If a cluster comprises more than one sector, the set of Logical Sector Numbers (LSN) of its constituent sectors shall form a consecutive ascending sequence. Each cluster shall be identified by a unique Cluster Number (CN). Cluster Numbers shall be integers, assigned in ascending order starting with 2. Cluster Number 2 shall be assigned to the cluster the first or only sector of which has the Logical Sector Number SSA. Each successive Cluster Number shall be assign- ed to the cluster the sectors of which have the next higher set of LSNs. If the total number of sectors in the Data Area is not a multiple of SC the remaining sectors shall not be used. The Logical Sector Number of the first sector in a cluster shall be related to the Cluster Number by the following formula : LSN [(CN - 2) x SCI + SSA where LSN is the Logical Sector Number; CN is the Cluster Number; SC is the number of sectors per cluster; SSA is the size of the System Area in number of sectors (see 6.3.4). 6.2.2 Status of clusters A status shall be assigned to each cluster, and shall be one of the following : - allocated to a file; - available for allocation; - defective. The status of each cluster shall be identified in the File Alloca- tion Table (FAT) in the System Area. 6.2.2.1 Clusters allocated to a file The clusters allocated to contain a file shall be identified in the FAT. The clusters allocated to contain a file need not have con- secutive Cluster Numbers. 6.2.2.2 Clusters available for allocation The clusters available for allocation shall be identified in the FAT. The clusters available for allocation need not have con- secutive Cluster Numbers. The contents of clusters available for allocation shall be ignored in interchange. 6.2.2.3 Defective Clusters Clusters containing one or more defective sectors shall be marked as Defective Clusters in the FAT. The contents of Defective Clusters shall be ignored in interchange. 4 SIST EN 29293:1997

IS0 9293 : 1987 (E) 6.3 Arrangement of the System Area The System Area shall contain an FDC Descriptor and space for system use, the Root Directory, and the File Allocation Table (FAT) recorded twice. 6.3.1 FDC Descriptor and space for system use The sector with Logical Sector Number O shall contain the FDC Descriptor and space for system use. The FDC Descriptor shall contain a Medium Identifier, the FDC parameters, an identifier of the system which recorded the FDC Descriptor and information about the parameters of the volume structure. Additional sectors having successively higher Logical Sector Numbers may also be reserved for system use. The contents of such sectors shall be ignored in interchange. The number of sectors reserved for system use (RSC) shall include the sector the LSN of which is O. The values of the Medium Identifier and the Reserved Sectors Count for each medium type shall be as specified in annex A. 6.3.2 File Allocation Table (FAT) The FAT shall contain a Format Identifier and one entry for each cluster of the Data Area of the FDC. These entries shall be numbered consecutively starting with 2 and the Entry Number shall be equal to the Cluster Number of the corresponding cluster. Each entry in the FAT shall indicate the status of the corre- sponding cluster. The FAT entries shall be used to identify the set of clusters that are allocated to each file. Annex D shows an example of a FAT. The number of sectors of the FAT (SF) shall be dependent on the number of clusters in the Data Area and shall be as specified in annex A. The FAT shall be recorded in the System Area, in a sequence of sectors starting with the Logical Sector Number equal to RSC. The second occurrence of the FAT shall be recorded in a se- quence of sectors immediately following the first occurrence of the FAT. 6.3.3 Root Directory The Root Directory shall be recorded in the System Area in a sequence of consecutive sectors immediately following the second occurrence of the FAT. It shall contain a set of entries each of which identifies a file, a Volume Label or a sub- directory, or indicates that it is not in use. The number of these entries, the Root Directory Entries (RDE), shall be as specified in annex A. 6.3.4 Size of the System Area The size of the System Area (SSA), in number of sectors, is given by the following formula : SSA = RSC + 2SF + ceil (32::E) - < NOS x SPT where RSC is the number of sectors preceding the first FAT, i.e. the Reserved Sectors Count; SF is the number of sectors in the FAT; RDE is the number of Root Directory Entries; SS is the number of bytes in the Data Field of a sector; NOS is the number of sides available for recording; SPT is the number of sectors per track. 6.4 Files A file shall be an interchange file or a Sub-directory or a file not intended for interchange. Each file shall be identified by an entry in a Directory. 6.4.1 File Space Each file shall be recorded in the Data Fields of the sectors of a set of clusters. This set shall be known as the File Space of the file. The order of the clusters within the set shall be specified by their FAT entries. The bytes in the File Space shall be numbered consecutively. The numbering shall start with 1, which shall be assigned to the first byte of the first cluster of the File Space. The numbering shall continue through successive bytes of the first cluster, and then through successive bytes of each successive cluster (if any) of the File Space. The numbering shall end with a number equal to the number of bytes per cluster (i.e. SS x SC) multiplied by the number of clusters in the File Space. 6.4.2 Relation to clusters The Cluster Numbers of the clusters forming the File Space of a file shall be recorded as a chain as follows : - The Cluster Number of the first cluster of the File Space shall be recorded in the Starting Cluster Number field of the Directory entry of the file. - For each cluster of the File Space, except the last one, the corresponding FAT entry shall contain the Cluster Number of the next cluster of the File Space. - For the last cluster of the File Space, the corresponding FAT entry shall contain an entry indicating that it is the last cluster of the file. 6.4.3 File length The length of a file shall be the number of consecutive bytes in the File Space, starting from the first byte, that are intended for interchange. It this number is less than the number of bytes in 5 SIST EN 29293:1997

IS0 9293 : 1987 (E) the File Space then any remaining bytes in the File Space shall be ignored in interchange. 6.5 Sub-directories In addition to the Root Directory in the System Area, additional Directories called Sub-directories may be recorded as files in the Data Area of the FDC. Sub-directories shall contain Direc- tory entries each of which identifies a file or another Sub- directory, or indicates that it is not used. The number of entries in a Sub-directory shall be calculated as follows : where K is the number of clusters allocated to the Sub- directory. Each Sub-directory shall be identified by one entry called a Sub-directory Pointer Entry in another directory. The Directory containing this Sub-directory Pointer Entry shall be called the Parent Directory of the Sub-directory. Each Sub- directory shall have a Parent Pointer Entry which points back to its Parent Directory. Different Sub-directories may have the same Parent Directory. A hierarchical relationship shall exist between the Root direc- tory and all Sub-directories : 7uBi SUB2 The hierarchy shall consist of a number of levels (level O, level 1, . 1. The Root Directory shall be the one and only directory at level O of the hierarchy. If a Parent Directory is at level n of the hierarchy, its Sub- directories shall be at level (n + 1 ). The number of levels of the hierarchy is limited only by a restriction on the length of the virtual path name which shall be calculated as follows. The length of the virtual path name shall be the sum of - the length of the file name; - if there is a file name extension, the length of the file name extension, plus 1; - the length of the names of all relevant Sub-directories; - the length of the name extensions of all relevant Sub- directories; - the number of relevant Sub-directories; - the number of name extensions of all relevant Sub- directories. 7 Contents of a file The information in an interchange file shall be interpreted according to the relevant International Standards for the coded representation of information. NOTE - The identification of the standard to which the coding of the information content of the file conforms is assumed to be the subject of an agreement between originator and recipient of the file. This Inter- national Standard makes no general provision for recording that iden- tification on the FDC. However, some selected standards may be iden- tified in the Name Extension Field of the File Entry of a Directory, see 11.5.1. 8 Recording of descriptor fields 8.1 Numerical values in one-byte fields A numerical value in a one-byte field shall be an 8-bit number recorded in binary notation. 8.2 Numerical values in two-byte fields A numerical value in a two-byte field shall be a 16-bit number the hexadecimal representation (wx yz) of which shall be recorded as (yz wxi. NOTE - For example, the decimal number 72 has (O0 48) as its hex- adecimal representation and is recorded as (48 00). 8.3 Numerical values in four-byte fields A numerical value in a four-byte field shall be a 32-bit number the hexadecimal representation (st UV wx yz) of which shall be recorded as (yz wx UV st). NOTE - For example, the decimal number 305419896 has (12 34 56 78) as its hexadecimal representation and is recorded as (78 56 34 12). 8.4 Pairs of 12-bit integers A pair of 12-bit numbers the hexadecimal representations of which are (abc) and (def) shall be recorded as (bc fa de). This method shall be used for FAT entries, NOTE - For example, the pair of 12-bit numbers with hexadecimal representations (123) and (456) is recorded as (23 61 45). 8.5 Character set and coding Unless otherwise stated, the characters in the Descriptors shall be coded according to IS0 646 (see annex Cl. The 37 characters in the following positions of the International Reference Version are referred to as d-characters : 310 to 319 411 to 5/10 5/15 This sum shall not exceed 63. 6 SIST EN 29293:1997

IS0 9293 : 1987 (El l The 57 characters in the following positions of the International Reference Version are referred to as a-characters : 210 to 212 215 to 2/15 310 to 3/15 411 to 4/15 510 to 5/10 5/15 8.6 Justification of characters In each field the content of which is specified by this Inter- national Standard to be d-characters, the d-characters shall be left-justified and any remaining positions on the right shall be set to (20). 9 FDC Descriptor The FDC Descriptor describes the format of the flexible disk cartridge and provides information about other Descriptors in the System Area of the FDC. 9.1 FDC Descriptor layout 1 to 3 4 to 11 12 and 13 14 15 and 16 17 18 and 19 20 and 21 22 23 and 24 25 and 26 27 and 28 29 and 30 31 to 512 9.2.2 Creating System Identifier (BP 4 to 11) This field shall specify an identification for the system that has recorded the FDC Descriptor. The characters in this field shall be a-characters. 9.2.3 Sector Size (BP 12 and 13) This field shall specify the size of the Data Field of a sector. It shall be recorded as a numerical value according to 8.2. 9.2.4 Sectors per Cluster (BP 14) This field shall specify the number of sectors per cluster. It shall be recorded as a numerical value according to 8.1. 9.2.5 Reserved Sector Count (BP 15 and 16) This field shall specify the number of sectors reserved for system use. It shall be recorded as a numerical value according to 8.2. 9.2.6 Number of FATs (BP 17) Table 3 Field name (Reserved for system use) Creating System Identifier Sector Size Sectors per Cluster Reserved Sector Count Number of FATs Root Directory Entries Total Sectors Medium Identifier Sectors per FAT Sectors per Track Number of Sides (Reserved for future standardization) (Fieserved for system use) 9cronym ss sc RSC FN RDE TS SF S PT NOS Content not specified a-characters numerical value numerical value numerical value Number 2 numerical value numerical value (FD) or (F91 numerical value numerical value numerical value (00) (00) not specified This field shall specify the number 2. It shall be recorded as a numerical value according to 8.1. 9.2.7 Root Directory Entries (BP 18 and 19) This field shall specify the number of entries in the Root Direc- tory. It shall be recorded as a numerical value according to 8.2. 9.2.8 Total Sectors (BP 20 and 21) This field shall specify the total number of sectors on the FDC (including defective sectors). It shall be recorded as a numerical value according to 8.2. 9.2.9 Medium Identifier (BP 22) This field shall specify an identification of the medium. It shall be recorded as a single byte. Its value shall be as specified in annex A. 9.2 FDC Descriptor fields 9.2.10 Sectors per FAT (BP 23 and 24) 9.2.1 This field shall be reserved for system use. Its content is not specified by this International Standard and shall be ignored in interchange. Field reserved for system use (BP 1 to 3) This field shall specify the number of sectors occupied by each occurrence of the FAT. It shall be recorded as a numerical value according to 8.2. 7 SIST EN 29293:1997

IS0 9293 : 1987 (E) 9.2.11 Sectors per Track (BP 25 and 26) This field shall specify the number of sectors in each track. It shall be recorded as a numerical value according to 8.2. 9.2.12 Number of Sides (BP 27 and 28) This field shall specify the number of recordable sides. It shall be recorded as a numerical value according to 8.2. 9.2.13 Field reserved for future standardization (BP 29 and 30) This field shall be reserved for future standardization. It shall contain only ZEROS. 9.2.14 Field reserved for system use (BP 31 to 512) This field shall be reserved for system use. Its contents are not specified by this International Standard and shall be ignored in interchange. 10 File Allocation Table The first three bytes of the FAT shall be used as follows: byte O shall contain the Format Identifier, bytes 1 and 2 shall each contain (FFI. The remaining bytes of the FAT shall contain FAT entries each of which shall indicate the status of the cluster associated with it. FAT entries shall be numbered starting with 2. 10.1 Format Identifier This field shall specify an identification for the source of the volume structure parameters. (F9) shall mean that these parameters are recorded in the FDC Descriptor. (FD) shall mean that these parameters shall be as specified in annex A for IS0 7487. All other values are prohibited from future use. 10.2 FAT entries 10.2.1 FAT entry size The length of each FAT entry shall be 12 bits. 10.2.2 Number of FAT entries The number of entries in the FAT shall be equal to the number of clusters. 10.2.3 FAT entry values The values for FAT entries shall be : MAX + 1 to (FF6) (FF7) (FF8) to (FFF) shall mean that the corresponding cluster is not in use and may be allocated to any File Space. shall mean that the corresponding cluster is in use; the entry value shall be the cluster number of the next cluster allocated in the File Space. MAX shall be the Maximum Cluster Number (see 10.2.4). are reserved for future standardization and shall not be used. shall mean that the corresponding cluster contains a defective sector. shall mean that the corresponding cluster is in use and is the last cluster of a File Space. 10.2.4 Maximum Cluster Number (MAX) The value for Maximum Cluster Number shall be calculated as follows: MAX=@( TS - SC SSA ) ~ , where TS is the total number of sectors on the medium; SSA is the number of sectors in the System Area; SC is the number of sectors per cluster. 10.3 Number of sectors in each FAT Each FAT shall occupy one or more sectors. The number of sectors per FAT (SF) shall be calculated by iteration from: : = ceii I -1 I 8 SS I where TS is the total number of sectors on the medium; SC is the number of sectors per cluster; SS is the sector data field size; RSC is the Reseved Sector Count; RDE is the number of entries in the Root Directory. 8 SIST EN 29293:1997

I) BP Field name 1 to 8 Name 9 to 11 Name Extension 12 Attributes 13 to 22 Reserved Field 23 and 24
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