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1、BRITISH STANDARD BS 4850-2: 1972 Incorporating Amendment No. 1 Specification for Magnetic six-disk packs for data processing Part 2: Track format UDC 681.327.63:621.3.037.3 Licensed Copy: sheffieldun sheffieldun, na, Fri Dec 01 01:59:32 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 4850-2:1972 This
2、British Standard, having been approved by the Data Processing Industry Standards Committee, was published under the authority of the Executive Board on 14 August 1972 BSI 12-1999 The following references relate to the work on this standard: Committee reference DPE/4 Draft for approval 71/35166 ISBN
3、0 580 07186 3 Co-operating organizations The Data Processing Industry Standards Committee, under whose supervision this British Standard was prepared, consists of representatives from the following Government departments and scientific and industrial organizations: Aslib British Computer Society* Br
4、itish Electrical and Allied Manufacturers Association British Federation of Master Printers British Paper and Board Makers Association British Telecommunications Research Ltd Business Equipment Trade Association* Civil Service Department* Committee of London Clearing Bankers* Data-Processing Managem
5、ent Association* Department of Trade and Industry National Physical Laboratory* Department of Trade and Industry Computer Advisory Service Technical Support Unit* Electricity Council, the Central Electricity Generating Board and the Area Boards in England and Wales* Electronic Engineering Associatio
6、n* Engineering Equipment Users Association Government Communications Headquarters Institute of Cost and Works Accountants Institute of Municipal Treasurers and Accountants (Incorporated) Institution of Electrical Engineers* Institution of Mechanical Engineers London Transport Executive Ministry of D
7、efence Royal Aircraft Establishment National Coal Board* National Computing Centre Limited National Research Development Corporation Post Office* Society of British Aerospace Companies* Technical Section of the British Paper and Board Makers Association Telecommunication Engineering and Manufacturin
8、g Association* The Government departments and scientific and industrial organizations marked with an asterisk in the above list, together with the following, were directly represented on the committee entrusted with the preparation of this British Standard: Department of the Environment H.M. Station
9、ery Office Institution of Electronic and Radio Engineers Ministry of Defence (STAN 10) Radio and Electronic Component Manufacturers Federation Scientific Instrument Manufacturers Association of Great Britain United Kingdom Atomic Energy Authority Amendments issued since publication Amd. No.Date of i
10、ssueComments 2033June 1976Indicated by a sideline in the margin Licensed Copy: sheffieldun sheffieldun, na, Fri Dec 01 01:59:32 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 4850-2:1972 BSI 12-1999i Contents Page Co-operating organizationsInside front cover Forewordii 1Scope1 2Definitions1 3General
11、requirements1 3.1Rotational speed and clock frequency1 3.2Mode of recording1 3.3Index1 3.4Track capacity1 3.5Track layout1 4Detailed description of track layout1 4.1Sector 01 4.2Subsequent sectors3 4.3Last sector3 Appendix A Rotational speed and clock frequency tolerance6 Appendix B Track capacity6
12、Figure 1 General track layout4 Figure 2 Home Address (Sector 0)4 Figure 3 Count (Sector 0)4 Figure 4 Key5 Figure 5 Data Block5 Figure 6 Count (other than Sector 0)5 Publications referred toInside back cover Licensed Copy: sheffieldun sheffieldun, na, Fri Dec 01 01:59:32 GMT+00:00 2006, Uncontrolled
13、Copy, (c) BSI BS 4850-2:1972 ii BSI 12-1999 Foreword This British Standard has been published under the authority of the Data Processing Industry Standards Committee. Work on magnetic disk packs began at the International Organization for Standardization (ISO) in June, 1968, with the setting up of a
14、 Working Group under the Secretariat of Germany. The first meeting of the Working Group took place in June, 1969, when it was quickly established that International Standards were desirable for a six-disk pack. Since that date, work on this standard has been carried out concurrently with the interna
15、tional discussions. It was realized that because of the rapid development taking place in the data processing industry, standardization on this initial project should be completed as quickly as possible. This Part of the standard specifies a variable length track format for six-disk packs, detailing
16、 the patterns of magnetization on the disks to be used to record Data Blocks of variable length with or without the use of keys. The specified format is based on current practice; disk packs recorded according to this Part of the standard and also conforming to the requirements of Part 1 of this Sta
17、ndard may be used for data interchange. It is the intention that future international work will be directed to the introduction of new format and labelling standards of more universal application, since limitations exist in the general use of the present standard for interchange. Use of binary code
18、within 8-bit groups (bytes or octets) is specified for control characters (some groups are specified in hexadecimal notation for convenience), and information in key and Data Blocks is also specified in 8-bit bytes, using the UK 7-bit data code (see BS 4730 “The United Kingdom 7-bit data code (ISO-7
19、-UK)”) or, by agreement between the sender and the recipient, any 7-bit or 8-bit code structured in accordance with BS 4953 “Code extension techniques for use with the United Kingdom 7-bit data code”. Use of binary code for control purposes avoids the need to modify existing equipment; most control
20、functions are usually implemented by hardware. Since control information is visible to operating system software, such an arrangement may not prove to be suitable for a general format specification for interchange between dissimilar systems. However, any future changes are unlikely to be applied to
21、six-disk systems. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This d
22、ocument comprises a front cover, an inside front cover, pages i and ii, pages 1 to 6, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover. Licensed
23、 Copy: sheffieldun sheffieldun, na, Fri Dec 01 01:59:32 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 4850-2:1972 BSI 12-19991 1 Scope This Part of this British Standard specifies the mode of recording and a variable length track format for interchange of data on magnetic six-disk packs. NOTE 1Track
24、 location and dimensions and the mechanical and magnetic properties of the disk packs are specified in BS 4850, “Magnetic six-disk packs for data processing”, Part 1, “Mechanical and magnetic properties”. NOTE 2The titles of the British Standards referred to in this standard are listed on the inside
25、 back cover. 2 Definitions For the purposes of this Part of this British Standard the following definitions apply: 2.1 sector a division of a track. A sector may be further subdivided 2.2 home address information which defines the physical location and characteristics of a track 2.3 count informatio
26、n which defines the physical location and characteristics of a sector 2.4 key an optional record identifier 2.5 data block part of a sector in which data is recorded 2.6 gap the space between the various divisions of a track 2.7 byte (or octet) 8 Serial bits, identified b8 to b1 with b8 as most sign
27、ificant and recorded first 2.8 hexadecimal notation (00)16 denotes a byte (or octet) with b8 to b1 = 00000000 (FF)16 denotes a byte (or octet) with b8 to b1 = 11111111 (0E)16 denotes a byte (or octet) with b8 to b1 = 00001110 (CC)16 denotes a byte (or octet) with b8 to b1 = 11001100 3 General requir
28、ements 3.1 Rotational speed and clock frequency. The nominal rotational speed shall be 2 400 rev/min. The total tolerance on rotational speed plus clock frequency shall not exceed 2.4 % (see Appendix A). 3.2 Mode of recording. The mode of recording shall be double frequency where every bit cell has
29、a clock transition. A ONE is represented by a transition between two clocks. At the nominal rotational speed of 2 400 rev/min an all ZEROS pattern shall consist of 1.25 106 transitions per second nominally, and an all ONES pattern shall consist of 2.50 106 transitions per second nominally. 3.3 Index
30、. The Index defines the beginning and end of a track. The physical location of the Index is specified in 3.1.5 of Part 1 of this standard. 3.4 Track capacity. The capacity of a track shall be 31 250bits (see Appendix B). 3.5 Track layout. The general track layout shall be as shown in Figure 1. 4 Det
31、ailed description of track layout 4.1 Sector 0. The first sector following the Index is unique in that it contains a Home Address and is therefore described separately. 4.1.1 Index gap (see Figure 2). 4.1.1.1 Starting from the Index, a gap of 30 bytes (00)16 shall be recorded as detailed in Figure 2
32、. Because of tolerances on the Index when reading, the Index Gap shall have a length of 30 14 bytes, of which the first 14 may be unreadable. 4.1.2 Home Address (see Figure 2). The Home Address shall consist of 14 bytes as follows. 4.1.2.1 Synchronization consists of 6 bytes, as follows: (00)16 (00)
33、16 (00)16 (00)16 (FF)16 (0E)16 4.1.2.2 F Flag (1 byte) is used to indicate defective and alternative tracks. The significance of the bits in this byte shall be as follows: The first two bits (b8 and b7) shall be always ZERO. b6 to b3 shall be reserved for future standardization and shall be all ZERO
34、. b2 b1 = 00 indicates good original track b2 b1 = 01 indicates good alternative track b2 b1 = 10 indicates defective track, alternative has been allocated b2 b1 = 11 indicates defective track, no alternative has been allocated. +768 733 Licensed Copy: sheffieldun sheffieldun, na, Fri Dec 01 01:59:3
35、2 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 4850-2:1972 2 BSI 12-1999 4.1.2.3 C Cylinder (2 bytes) is used to specify in binary the address of the cylinder. The first byte shall be always ZERO. The second byte may have any value in the range 0 to 202. 4.1.2.4 H Head (2 bytes) is used to specify
36、in binary the address of a track within a cylinder. The first byte shall be always ZERO. The second byte may have any value in the range 0 to 9. 4.1.2.5 CRC Cyclic redundancy check (2 bytes) consists of the ONES complement of the remainder obtained after dividing the previous 5 information bytes by
37、the code polynomial (1 + x16). It may be used for error checking when reading. 4.1.2.6 The Home Address shall end with 1 byte (CC)16. 4.1.3 Home Address gap. An 11-byte gap shall be recorded between the end of the Home Address and the start of the Count. This gap may subsequently become undefined be
38、cause of repeated writing operations. The gap shall be written initially as (00)16. 4.1.4 Count of Sector 0 (see Figure 3). The Count shall consist of 18 bytes as follows. 4.1.4.1 Synchronization consists of 6 bytes, as follows: (00)16 (00)16 (00)16 (00)16 (FF)16 (0E)16 4.1.4.2 F Flag (1 byte) is us
39、ed for certain control and checking operations and to indicate defective and alternative tracks. The significance of the bits in this byte shall be as follows: b8 = ZERO for Sector 0. See 4.2.1.2 for the use of this bit in other sectors. b7 = ZERO for Sector 0. See 4.2.1.2 for the use of this bit in
40、 other sectors. b6 to b3 shall be reserved for future standardization and shall be all ZERO. b2 and b1. The state of these bits shall be always the same as those in the Home Address (see 4.1.2.2). 4.1.4.3 C and H Cylinder and Head (4 bytes) are identical to those in the Home Address except when appe
41、aring on defective or alternative tracks. On a defective track C and H contain cylinder and head number of the alternative track which replaces it. On an alternative track C and H contain cylinder and head number of the defective track which it replaces. 4.1.4.4 S Sector (1 byte) is used to identify
42、 sectors on the track. 4.1.4.5 KL Key length (1 byte) is used to specify in binary the number of information bytes in the Key. 4.1.4.6 DL Data length (2 bytes) is used to specify in binary the number of information bytes in the Data Block. 4.1.4.7 CRC Cyclic redundancy check (2 bytes) consists of th
43、e ONES complement of the remainder obtained after dividing the previous 9 information bytes by the code polynomial (1 + x16). It may be used for error checking when reading. 4.1.4.8 The Count shall end with 1 byte (CC)16. 4.1.5 Count gap. An 11-byte gap shall be recorded between the end of the Count
44、 and the start of the Key. This gap may subsequently become undefined because of repeated writing operations. The gap shall be written initially as 9 bytes of (FF)16 followed by 2 bytes of (00)16. 4.1.6 Key (see Figure 4). The Key shall consist of (KL + 9) bytes, where KL is the number of informatio
45、n bytes (see 4.1.4.5). If KL in the preceding Count is ZERO, the Key and the following gap (see 4.1.7) shall be omitted and the Count shall be followed by the Data Block (see 4.1.8). Otherwise the Key shall be as follows. 4.1.6.1 Synchronization consists of 6 bytes, as follows: (00)16 (00)16 (00)16
46、(00)16 (FF)16 (0E)16 4.1.6.2 Information consists of a number of information bytes as specified in the KL portion of the preceding Count. For the purposes of data interchange, the data in these bytes will be assumed to be recorded in the UK 7-bit data code (see BS 4730) unless agreed by sender and r
47、ecipient to be some other 7-bit or 8-bit code structured in accordance with BS 4953. The bits of these codes shall be recorded as follows: 1) A 7-bit coded character shall be recorded in the seven least significant bit positions of each byte such that bits b7 to b1 of the coded character shall be re
48、corded in positions b7 to b1 respectively as defined in 2(7). b8 shall be always ZERO. 2) An 8-bit coded character shall be recorded such that bits a8 to a1 of the coded character shall be recorded in positions b8 to b1 respectively as defined in 2(7). 4.1.6.3 CRC Cyclic redundancy check (2 bytes) c
49、onsists of the ONES complement of the remainder obtained after dividing the previous information bytes by the code polynomial (1 + x16). It may be used for error checking when reading. 4.1.6.4 The Key shall end with 1 byte (CC)16. Licensed Copy: sheffieldun sheffieldun, na, Fri Dec 01 01:59:32 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 4850-2:1972 BSI 12-19993 4.1.7 Key gap. An 11-byte gap shall be recorded between the end of the Key and the start of the Data Block. The gap may subsequently become undefin
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