ISO 9293:1987

:so
INTERNATIONAL STANDARD ,293
'irst edition
987-04-15
INTERNATIONAL ORGANIZATION FOR STANDARDIZATION
DE NORMALISATION
ORGANISATION INTERNATIONALE
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
Reference number
170 9293 : 1987 (E)
&!
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
IS0 9293 : 1987 (E)
Contents Page
Section one : General
.........................................................
O Introduction 1
1 Scope and field of application .
2 Conformance .
2.1 Conformance of a flexible disk cartridge . 2
Conformance of an information processing system .
2.2 2
..........................................................
3 References 2
..........................................................
4 Definitions 2
4.1 byte .
............................................
4.2 data field of a sector 2
4.3 data interchange standard .
................................................
4.4 defective sector 2
4.5 descriptor .
4.6 file .
4.7 formatting . 2
4.8 implementation .
4.9 initialization .
4.10 originating system .
4.11 receiving system .
4.12 sector .
.........................................................
4.13 track 3
4.14 user . 3
4.15 fixed-length record .
4.16 record .
4.17 segment .
4.18 segmented record .
4.19 variable-length record .
...........................................................
5 Notations 3
5.1 Decimal and hexadecimal notations . 3
5.2 Other notations .
5.3 Capital letters . 3
Section two : Requirements for the medium
....................................................
6 Volume structure 3
Arrangement of data on a flexible disk cartridge . 3
6.1
6.1.1 FDC parameters .
6.1.2 Physical Addresses .
6.1.3 Logical Sector Number .
6.1.4 System Area and Data Area . 4
6.1.5 Parameters of the Volume Structure . 4
Arrangement of the Data Area .
6.2 4
6.2.1 Clusters .
6.2.2 Status of clusters .
Arrangement of the System Area .
6.3 5
6.3.1 FDC Descriptor and space for system use . 5
6.3.2 File Allocation Table (FAT) . 5
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 .
................................................
6.5 Sub-directories
.....................................................
7 Contents of a file
iii
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 Field reserved for system use (BP 1 to 3) . 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
11.3.6 Date Recorded (BP25and26) . 10
11.3.7 Starting Cluster Number (BP27and28) .
11.3.8 File Length (BP 29 to 32) . 10
File Entry .
11.4.1 Name (BP 1 to8) .
11.4.2 Name Extension (BP9 to 11) . 10
11.4.3 Attributes (BP 12) .
11.4.4 Reserved Field (BP 13 to22) . 10
11.4.5 Time Recorded (BP23and24) .
11.4.6 Date Recorded (BP 25 and 26) . 10
11.4.7 Starting Cluster Number (BP 27and 28) .
11.4.8 File Length (BP29to32) . 10
Volume Label Entry .
11.5.1 Nameand Name Extension (BP 1 to 11) . 10
11.5.2 Attributes (BP 12) .
*
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
11.5.7 File Length (BP 29 to 32) . 11
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
11.6.8 File Length (BP29to32) .
11.7 Sub-directory Identifier Entry .
11.7.1 Name(BP1 to8) . 11
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
11.7.8 File Length (BP29to32) .
Sub-directory Parent Pointer entry .
11.8 12
11.8.1 Name(BP1 to81 . 12
11.8.2 NameExtension(BP9toll) .
11.8.3 Attributes (BP 12) .
11.8.4 Reserved Field (BP 13 to221 . 12
11.8.5 Time Recorded (BP 23 and 24) . 12
11.8.6 Date Recorded (BP25and 26) . 12
11.8.7 Starting Cluster Number (BP27and 28) . 12
11.8.8 FileLength(BP29to32) .
11.9 Not-currently-used Entry .
11.9.1 Name Field (BP 1 to 18) . 12
11.9.2 Remaining bytes (BP9 to32) . 12
11.10 Never-used Entry .
11.10.1 NameField(BP1 to81 .
11.10.2 Remaining bytes (BP 9 to 32) . 12
Section three: Requirements for systems
12 Requirements for the description of systems . 13
13 Requirementsfor an originating system . 13
......................................................
13.1 General 13
.........................................................
13.2 Files 13
13.3 Descriptors . 13
14 Requirements for a receiving system . 13
......................................................
14.1 General 13
.........................................................
14.2 Files 13
14.3 Descriptors . 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
..I
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
__ ~~
INTERNATIONAL STANDARD IS0 9293 : 1987 (E)
Information processing - Volume and file structure
of flexible disk cartridges for information interchange
Section one : General
O Introduction - interchange of any file when sender and recipient wish to
carry out frequent update of the file between interchange
For many purposes IS0 7665 provides a satisfactory data inter- cycles, for example files of commercial transactions.
change between different types of information-processing
systems. However, it imposes some restrictions on the opera-
tion of a system as follows :
1 Scope and field of application
a) Each individual file must be recorded on the disk in a se-
This International Standard specifies the volume and file struc-
quential, "batch-processing" mode. After a set of files has
ture of flexible disk cartridges (FDC) for the interchange of
been recorded on the disk, a file cannot be extended beyond
information between users of information processing systems.
its pre-determined length.
It also specifies an optional record structure.
It is common practice in small systems for the user to inter- This International Standard is applicable to various types of
act continuously with the system to update files. Files
flexible disk cartridges including those identified in clause 3,
having a suitable structure for this purpose are not within and other types which may be the subject of future Inter-
the provision of IS0 7665.
national Standards.
The interchange cartridge has to be created by an "export" This International Standard specifies the location of files of in-
copy process from the application's files, after the applica-
formation on a flexible disk cartridge, and also specifies a set of
tion has terminated. A similar "import" process is required
recorded descriptors which identifies :
in the receiving system.
- the files which may be interchanged;
b) Limitations on the number of file labels permitted on an
interchange FDC prevents the full use of the disk space if - the locations of the files:
the average size of files is significantly less than, say
- the attributes of the files;
20 kbytes. For conventional data processing purposes this
is usually satisfactory. However, the file sizes typically en-
- the location of unused space for recording on the FDC;
countered in text processing and small single-user systems
are very much smaller and would lead to very inefficient use
- the location of defective recording space on the FDC;
of the disk space.
- the attributes of the FDC and of the descriptors recorded
In view of these requirements it was decided to develop a
on it.
second standard for volume and file structure of flexible disk
cartridges, the provisions of which were to be based on already
This International Standard also specifies requirements for the
existing practice in general use world-wide. Hence this Inter-
processes which are provided within information processing
national Standard has the following beneficial characteristics,
systems to enable information to be interchanged between dif-
in addition to those of IS0 7665.
ferent systems, utilizing recorded flexible disk cartridges as the
medium of interchange. For this purpose it specifies the func-
- The interchange file will be especially for direct updating
tions within systems which are intended to originate or to
by interactive application.
receive flexible disk cartridges which conform to this Inter-
national Standard.
- 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. This International Standard provides a method for the alloca-
tion of space that is independent of the number of files that are
These characteristics are advantageous for : recorded on the volume, It also enables the sizes of the record-
ed files to be expanded or contracted during processing, sub-
- interchange of sets of text files or of small files, or of
ject only to the availability of unused recording space when
multiple-part document files;
needed.
IS0 9293 : 1987 (E)
The contents and organization of the files are not specified by frequency modulation recording at 13 262 ftprad, 3,8 tpmm
this International Standard and are subject to agreement be- (96 tpi), on both sides
tween the originator and the recipient of the interchanged FDC.
- Part 7: Dimensional, physical and magnetic character-
istics. 1 )
2 Conformance
- Part 3: Track format B for 80 tracks. 1)
2.1 Conformance of a flexible disk cartridge
IS0 8860, Information processing - Data interchange on
90 mm (3.5 in) flexible disk cartridges using modified frequency
A flexible disk cartridge shall be in conformance with this Inter-
modulation recording at 7 958 ftprad, 5,3 tpmm (135 tpi), on
national Standard when all information recorded on it conforms
both sides
to the requirements of section 2 of this International Standard.
- Part 7: Dimensional, physical and magnetic character-
A prerequisite to such conformance is the conformance of the
istics.
flexible disk cartridge to the appropriate International Standard
for data interchange of flexible disk cartridges.
- Part 2: Track format.
2.2 Conformance of an information processing
system
4 Definitions
An information processing system shall be in conformance with
For the purposes of this International Standard the following
this International Standard if it meets the set of requirements
definitions apply.
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 4.1 byte: A string of binary digits operated upon as a unit.
In this International Standard this term designates an 8-bit
these sets of requirements is met by the system.
byte.
Conformance with this lnternation Standard does not require
conformance with section 4.
4.2 data field of a sector: A fixed-length field containing
the data of a sector.
3 References
4.3 data interchange standard : A standard which defines
the physical and magnetic characteristics, the recording
IS0 646, Information processing - IS0 7-bit coded character
method, and the track format of a flexible disk cartridge.
set for information interchange.
4.4 defective sector: A sector which cannot be read or
IS0 7487, Information processing - Data interchange on
written without error.
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
4.5 descriptor : A recorded structure containing descriptive
information about the volume or a file.
- Part 7: Dimensional, physical and magnetic character-
istics.
4.6 file: A named collection of information.
- Part 3: Track format B.
4.7 formatting : Writing the control information establishing
the physical addresses of sectors on the surfaces of a flexible
IS0 7665, Information processing - File structure andlabelling
of flexible disk cartridges for information interchange. disk cartridge.
IS0 8378, Information processing - Data interchange on
4.8 implementation: A set of processes which enable an
130 mm (5.25 in) flexible disk cartridges using modified fre-
information processing system to behave as an originating
7 958 ftprad, 3,8 tpmm
quency modulation recording at
system, or as a receiving system, or as both types of system.
(96 tpi), on both sides
4.9 initialization : Writing descriptors initially required to be
- Part I: Dimensional, physical and magnetic character-
on the FDC, prior to the commencement of general processing
istics.
or use.
- Part 3: Track format B.
4.10 originating system : An information processing
IS0 8630, Information processing - Data interchange on
system which can record files on an FDC for the purpose of
130 mm (5.25 in) high density flexible cartridges using modified
data interchange with another system.
1) At present at the stage of draft.
IS0 9293 : 1987 (E)
4.11 receiving system : An information processing system 5 Notation4
I
which can read files from an FDC which has been recorded by
another system for the purpose of data interchange. this International Standard.
4.12 sector: That part of a track on a flexible disk cartridge
5.1 Decimal and hexadecimal notations
that can be accessed independently of other parts of the track
by the magnetic heads of the flexible disk drive.
Numbers in decimal notation are represented by decimal digits,
namely O to 9.
4.13 track : That part of a flexible disk that can be accessed
by a single magnetic head that is stationary while the disk
Numbers in hexadecimal notation are represented by hexa-
makes a complete revolution.
decimal digits, namely O to 9 and A to F, shown in parentheses.
4.14 user: A person or other entity (for example an applica-
tion program) that causes the invocation of the services provid-
5.2 Other notations
ed by an implementation.
BP : Byte position within a Descriptor, starting with 1
In addition the following definitions apply specifically to section
four.
ZERO : A single bit with the value O
fixed-length record: A record contained in a file in
4.15 ONE: A single bit with the value 1
which all records must have the same length.
ip (x) : The integer part of x
record : Related data treated as a unit of information.
4.16
ceil(x) : The smallest integer that is not less than x
4117 segment : A part of a record.
rem(x,y) : The remainder of the integer division of x by y, that
is, rem(x,y) = x - y x ip(xJy)
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.
5.3 Capital letters
Where a word or a group of words is used to designate a
4.19 variable-length record : A record contained in a file in
it
which the records may have different lengths but a record must specific concept, for example the name of a descriptor field,
not consist of separate segments. is printed with initial capital letters except for prepositions.
Section two : Requirements for the medium
6 Volume structure 6.1.2 Physical Addresses
/
Each sector shall be identified by a Physical Address compris-
6.1 Arrangement of data on a flexible disk
ing the Side Number, the Track Number, and the Sector
cartridge
Number. The sides shall be numbered O and 1, tracks shall be
numbered starting with 00, and the sectors shall be numbered
6.1.1 FDC parameters
starting with 1 on each track.
For the purpose of this International Standard the significant
6.1.3 Logical Sector Number
parameters of the data interchange standard are shown in
table 1. /
Each sector on a volume shall be identified by a Logical Sector
Number. There shall be a one-to-one correspondence between
Table 1
Physical Address and Logical Sector Number. The Logical
FDC parameters Acronym
Sector Numbers shall be assigned in an ascending sequence,
beginning with O, starting at sector 1, track 00, side O, continu-
Number of Recordable Sides
ing onto track 00, side 1 (if the FDC is recordable on both
Number of Tracks per Side
sides) and then to track 01, side O, etc.
Number of Sectors per Track
Total Number of Sectors of the FDC
The relation between the Side Number (“1, Track Number
Number of Bytes per Data Field of a Sector
(TN), Sector Number (SN) and the Logical Sector Number
(LSN) shall be given by the formulae:
The values of these parameters shall be obtained from the text
of an appropriate data interchange standard (see annex A),
LSN = SPT x [HN + (NOS x TN)I + SN - 1
IS0 9293 : 1987 (E)
SN = rem (rem [LSN, (SPT x NOS)], SPT} + 1 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
{rem [LSN,(SPT x NOS11
HN = ip
of LSNs.
S PT
If the total number of sectors in the Data Area is not a multiple
6.1.4 System Area and Data Area
of SC the remaining sectors shall not be used.
The space on an FDC shall be divided into a System Area and a
The Logical Sector Number of the first sector in a cluster shall
Data Area.
be related to the Cluster Number by the following formula :
The System Area shall be recorded on track 00, side O and
LSN [(CN - 2) x SCI + SSA
track 00. side 1.
where
The System Area shall occupy sectors with the Logical Sector
Numbers O to SSA - 1, where SSA is the number of sectors in
LSN is the Logical Sector Number;
the System Area (see 6.3.4). The System Area shall contain
Descriptors which specify the recording format of the FDC,
CN is the Cluster Number;
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
SC is the number of sectors per cluster;
the System Area.
SSA is the size of the System Area in number of sectors
The Data Area shall occupy sectors with Logical Sector
(see 6.3.4).
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
6.2.2 Status of clusters
contained in the Data Area.
A status shall be assigned to each cluster, and shall be one of
6.1.5 Parameters of the Volume Structure
the following :
This International Standard specifies various types of data
- allocated to a file;
structure within the System Area and Data Area. The sizes of
these data structures are identified by a set of numerical
- available for allocation;
parameters. These parameters are listed in table 2.
- defective.
Table 2
The status of each cluster shall be identified in the File Alloca-
tion Table (FAT) in the System Area.
I Parameter I Acronym
Sectors per Cluster sc
Reserved Sector Count RSC
6.2.2.1 Clusters allocated to a file
Sectors per FAT SF
Root Directory Entries RDE
The clusters allocated to contain a file shall be identified in the
FAT. The clusters allocated to contain a file need not have con-
The values of these parameters for each FDC type are contain- secutive Cluster Numbers.
ed in annex A.
6.2.2.2 Clusters available for allocation
6.2 Arrangement of the Data Area
The clusters available for allocation shall be identified in the
6.2.1 Clusters
FAT. The clusters available for allocation need not have con-
secutive Cluster Numbers.
The Data Area shall be organized into units of allocation called
clusters. Each cluster shall consist of the same number of
The contents of clusters available for allocation shall be ignored
sectors which shall be a power of 2, i.e. 1, 2, 4, 8, . . The
in interchange.
number of sectors in each cluster (Sectors per Cluster, SC)
shall be as specified in annex A. The data of a cluster shall be
6.2.2.3 Defective Clusters
recorded in the Data Fields of its constituent sectors.
If a cluster comprises more than one sector, the set of Logical
Clusters containing one or more defective sectors shall be
Sector Numbers (LSN) of its constituent sectors shall form a
marked as Defective Clusters in the FAT. The contents of
consecutive ascending sequence.
Defective Clusters shall be ignored in interchange.
IS0 9293 : 1987 (E)
6.3 Arrangement of the System Area
SSA = RSC + 2SF + ceil - < NOS x SPT
The System Area shall contain an FDC Descriptor and space for
system use, the Root Directory, and the File Allocation Table
where
(FAT) recorded twice.
RSC is the number of sectors preceding the first FAT, i.e.
the Reserved Sectors Count;
6.3.1 FDC Descriptor and space for system use
SF is the number of sectors in the FAT;
The sector with Logical Sector Number O shall contain the FDC
Descriptor and space for system use.
RDE is the number of Root Directory Entries;
The FDC Descriptor shall contain a Medium Identifier, the FDC
SS is the number of bytes in the Data Field of a sector;
parameters, an identifier of the system which recorded the FDC
Descriptor and information about the parameters of the volume
NOS is the number of sides available for recording;
structure.
SPT is the number of sectors per track.
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
6.4 Files
sectors reserved for system use (RSC) shall include the sector
the LSN of which is O.
A file shall be an interchange file or a Sub-directory or a file not
intended for interchange.
The values of the Medium Identifier and the Reserved Sectors
Count for each medium type shall be as specified in annex A.
Each file shall be identified by an entry in a Directory.
6.3.2 File Allocation Table (FAT)
6.4.1 File Space
The FAT shall contain a Format Identifier and one entry for
Each file shall be recorded in the Data Fields of the sectors of a
each cluster of the Data Area of the FDC. These entries shall be
set of clusters. This set shall be known as the File Space of the
numbered consecutively starting with 2 and the Entry Number
file. The order of the clusters within the set shall be specified by
shall be equal to the Cluster Number of the corresponding
their FAT entries.
cluster.
The bytes in the File Space shall be numbered consecutively.
Each entry in the FAT shall indicate the status of the corre-
The numbering shall start with 1, which shall be assigned to the
sponding cluster. The FAT entries shall be used to identify the
first byte of the first cluster of the File Space. The numbering
set of clusters that are allocated to each file. Annex D shows an
shall continue through successive bytes of the first cluster, and
example of a FAT.
then through successive bytes of each successive cluster (if
any) of the File Space. The numbering shall end with a number
The number of sectors of the FAT (SF) shall be dependent on
equal to the number of bytes per cluster (i.e. SS x SC)
the number of clusters in the Data Area and shall be as
multiplied by the number of clusters in the File Space.
specified in annex A.
6.4.2 Relation to clusters
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- The Cluster Numbers of the clusters forming the File Space of a
file shall be recorded as a chain as follows :
quence of sectors immediately following the first occurrence of
the FAT.
- The Cluster Number of the first cluster of the File Space
shall be recorded in the Starting Cluster Number field of the
6.3.3 Root Directory
Directory entry of the file.
The Root Directory shall be recorded in the System Area in a
- For each cluster of the File Space, except the last one,
sequence of consecutive sectors immediately following the
the corresponding FAT entry shall contain the Cluster
second occurrence of the FAT. It shall contain a set of entries
Number of the next cluster of the File Space.
each of which identifies a file, a Volume Label or a sub-
directory, or indicates that it is not in use.
- For the last cluster of the File Space, the corresponding
FAT entry shall contain an entry indicating that it is the last
The number of these entries, the Root Directory Entries (RDE),
cluster of the file.
shall be as specified in annex A.
6.4.3 File length
6.3.4 Size of the System Area
The length of a file shall be the number of consecutive bytes in
The size of the System Area (SSA), in number of sectors, is
the File Space, starting from the first byte, that are intended for
given by the following formula :
interchange. It this number is less than the number of bytes in
(32::E)
IS0 9293 : 1987 (E)
the File Space then any remaining bytes in the File Space shall
7 Contents of a file
be ignored in interchange.
The information in an interchange file shall be interpreted
according to the relevant International Standards for the coded
6.5 Sub-directories
representation of information.
In addition to the Root Directory in the System Area, additional
NOTE - The identification of the standard to which the coding of the
Directories called Sub-directories may be recorded as files in
information content of the file conforms is assumed to be the subject
the Data Area of the FDC. Sub-directories shall contain Direc-
of an agreement between originator and recipient of the file. This Inter-
tory entries each of which identifies a file or another Sub-
national Standard makes no general provision for recording that iden-
directory, or indicates that it is not used.
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
The number of entries in a Sub-directory shall be calculated as
11.5.1.
follows :
8 Recording of descriptor fields
8.1 Numerical values in one-byte fields
where K is the number of clusters allocated to the Sub-
directory.
A numerical value in a one-byte field shall be an 8-bit number
Each Sub-directory shall be identified by one entry called a recorded in binary notation.
Sub-directory Pointer Entry in another directory.
8.2 Numerical values in two-byte fields
The Directory containing this Sub-directory Pointer Entry shall
be called the Parent Directory of the Sub-directory. Each Sub-
A numerical value in a two-byte field shall be a 16-bit number
directory shall have a Parent Pointer Entry which points back to
the hexadecimal representation (wx yz) of which shall be
its Parent Directory. Different Sub-directories may have the
recorded as (yz wxi.
same Parent Directory.
NOTE - For example, the decimal number 72 has (O0 48) as its hex-
A hierarchical relationship shall exist between the Root direc-
adecimal representation and is recorded as (48 00).
tory and all Sub-directories :
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
(yz wx UV st).
recorded as
7uBi SUB2
NOTE - For example, the decimal number 305419896 has
(12 34 56 78) as its hexadecimal representation and is recorded as
The hierarchy shall consist of a number of levels (level O,
(78 56 34 12).
level 1, . 1. The Root Directory shall be the one and only
directory at level O of the hierarchy.
8.4 Pairs of 12-bit integers
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
A pair of 12-bit numbers the hexadecimal representations of
hierarchy is limited only by a restriction on the length of the
which are (abc) and (def) shall be recorded as (bc fa de). This
virtual path name which shall be calculated as follows.
method shall be used for FAT entries,
The length of the virtual path name shall be the sum of
NOTE - For example, the pair of 12-bit numbers with hexadecimal
representations (123) and (456) is recorded as (23 61 45).
- the length of the file name;
- if there is a file name extension, the length of the file
8.5 Character set and coding
name extension, plus 1;
Unless otherwise stated, the characters in the Descriptors shall
- the length of the names of all relevant Sub-directories;
be coded according to IS0 646 (see annex Cl.
- the length of the name extensions of all relevant Sub-
directories; The 37 characters in the following positions of the International
Reference Version are referred to as d-characters :
- the number of relevant Sub-directories;
310 to 319
- the number of name extensions of all relevant Sub-
directories.
411 to 5/10
This sum shall not exceed 63.
5/15
IS0 9293 : 1987 (El
9.2.2 Creating System Identifier (BP 4 to 11)
The 57 characters in the following positions of the International
Reference Version are referred to as a-characters :
This field shall specify an identification for the system that has
210 to 212
recorded the FDC Descriptor.
215 to 2/15
The characters in this field shall be a-characters.
310 to 3/15
9.2.3 Sector Size (BP 12 and 13)
411 to 4/15
510 to 5/10 This field shall specify the size of the Data Field of a sector.
5/15
It shall be recorded as a numerical value according to 8.2.
8.6 Justification of characters
9.2.4 Sectors per Cluster (BP 14)
In each field the content of which is specified by this Inter-
This field shall specify the number of sectors per cluster.
national Standard to be d-characters, the d-characters shall be
left-justified and any remaining positions on the right shall be
It shall be recorded as a numerical value according to 8.1.
set to (20).
9.2.5 Reserved Sector Count (BP 15 and 16)
9 FDC Descriptor
The FDC Descriptor describes the format of the flexible disk This field shall specify the number of sectors reserved for
in
cartridge and provides information about other Descriptors system use.
the System Area of the FDC.
It shall be recorded as a numerical value according to 8.2.
9.1 FDC Descriptor layout
9.2.6 Number of FATs (BP 17)
Table 3
This field shall specify the number 2.
9cronym Content
Field name
It shall be recorded as a numerical value according to 8.1.
(Reserved for not specified
1 to 3
system use)
4 to 11 Creating System a-characters
9.2.7 Root Directory Entries (BP 18 and 19)
Identifier
Sector Size ss numerical value
12 and 13
This field shall specify the number of entries in the Root Direc-
14 Sectors per Cluster sc numerical value tory.
15 and 16 Reserved Sector RSC numerical value
It shall be recorded as a numerical value according to 8.2.
Count
Number of FATs FN Number 2
18 and 19 Root Directory RDE numerical value
9.2.8 Total Sectors (BP 20 and 21)
Entries
20 and 21 Total Sectors TS numerical value This field shall specify the total number of sectors on the FDC
(including defective sectors).
Medium Identifier
22 (FD) or (F91
23 and 24 Sectors per FAT SF numerical value
It shall be recorded as a numerical value according to 8.2.
Sectors per Track S PT numerical value
25 and 26
l
27 and 28 Number of Sides NOS numerical value
9.2.9 Medium Identifier (BP 22)
(Reserved for future
29 and 30 (00) (00)
standardization)
This field shall specify an identification of the medium.
(Fieserved for not specified
31 to 512
system use)
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)
Field reserved for system use (BP 1 to 3)
9.2.1
This field shall specify the number of sectors occupied by each
occurrence of the FAT.
This field shall be reserved for system use. Its content is not
specified by this International Standard and shall be ignored in
It shall be recorded as a numerical value according to 8.2.
interchange.
IS0 9293 : 1987 (E)
10.2.3 FAT entry values
9.2.11 Sectors per Track (BP 25 and 26)
This field shall specify the number of sectors in each track. The values for FAT entries shall be :
It shall be recorded as a numerical value according to 8.2. shall mean that the corresponding
cluster is not in use and may be
allocated to any File Space.
9.2.12 Number of Sides (BP 27 and 28)
shall mean that the corresponding
This field shall specify the number of recordable sides.
cluster is in use; the entry value shall
be the cluster number of the next
It shall be recorded as a numerical value according to 8.2.
cluster allocated in the File Space.
MAX shall be the Maximum Cluster
9.2.13 Field reserved for future standardization (BP 29
Number (see 10.2.4).
and 30)
MAX + 1 to (FF6)
are reserved for future standardization
This field shall be reserved for future standardization. and shall not be used.
It shall contain only ZEROS. (FF7) shall mean that the corresponding
cluster contains a defective sector.
9.2.14 Field reserved for system use (BP 31 to 512)
(FF8) to (FFF)
shall mean that the corresponding
cluster is in use and is the last cluster
This field shall be reserved for system use.
of a File Space.
Its contents are not specified by this International Standard and
shall be ignored in interchange. 10.2.4 Maximum Cluster Number (MAX)
The value for Maximum Cluster Number shall be calculated as
follows:
10 File Allocation Table
MAX=@( TS - SC SSA ) ~ ,
The first three bytes of the FAT shall be used as follows:
byte O shall contain the Format Identifier, bytes 1 and 2 shall
where
each contain (FFI.
TS is the total number of sectors on the medium;
The remaining bytes of the FAT shall contain FAT entries each
of which shall indicate the status of the cluster associated with
SSA is the number of sectors in the System Area;
it. FAT entries shall be numbered starting with 2.
SC is the number of sectors per cluster.
10.1 Format Identifier
10.3 Number of sectors in each FAT
This field shall specify an identification for the source of the
volume structure parameters.
Each FAT shall occupy one or more sectors. The number of
sectors per FAT (SF) shall be calculated by iteration from:
(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.
: = ceii I -1
All other values are prohibite
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