

                               Explanation of NSR




                                  April 1996

                               FUJITSU LIMITED







All Rights Reserved, COPYRIGHT (C) FUJITSU LIMITED 1994-1996





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1. Overview
===========

NSR is an acronym for the international standard logical format of 
optical disks.
 NSR stands for Non-Sequential Recording.
The so-called IBM format, or the super floppy format, is also a standard 
logical format for 3.5-inch magneto-optical disks. 
The IBM format was presented by IBM when 128-Mbyte drives were released.
The super floppy format and the NSR format are the world's two major 
standards of optical disks. 
The differences between the two formats are roughly described below.

  ------------------------------------------------------
  Super floppy              NSR
  ------------------------------------------------------
  Single partition *1       Multiple partitions *2
  Single OS        *3       Multiple OSs        *4
  Single disk               Multiple disk management  *5
  ------------------------------------------------------
  *1)  Like a floppy disk, the entire MO disk is assigned a drive letter.
  *2)  Like a hard disk, an MO disk can be partitioned, with different 
       drive names assigned to each partition.
  *3)  An MO disk can store DOS files only.
  *4)  An MO disk can store files of DOS and other operating systems 
       such as Mac.
  *5)  Multiple disks can be managed for use by libraries, for example.

  The super floppy format is simple, understandable, and easy to use.
  The NSR format is a prospective format with advanced functions.
  In short, the super floppy format is an extension of floppy disks, 
  and the NSR format is an extension of hard disks.



2. Why NSR is necessary
=======================

Some people thought it would be convenient to partition an MO disk just 
like a hard disk. 
There was a problem, however, when it came to applying the hard disk format 
to an MO disk; 
  IBM PC/AT compatibles, Mac disk format, and Japanese proprietary PC 
  series used different, incompatible hard disk formats. 
  Data was not interchangeable on hard disks. Thus, NSR was developed 
  as a standard format for these DOS machines.



3. World standard
=================

Data is exchanged via removable media, such as optical disks and floppy disks.
The data, however, cannot be exchanged correctly if the source and 
destination disk formats are different.
The International Standardization Organization, or ISO, is making 
international standards to simplify data exchange based on removable 
media such as optical disks. 
For example, ISO gave the ISO13346 number to the NSR format (December 1993).
The NSR format is not very popular yet. 
However, the number of machines using this format is increasing gradually.



4. Remarks
==========

The NSR format standard is in two parts:
- Volume format
- File format
The above explanation applies to the volume format part. 
In short, the volume format is the standard for disk partitioning.
The file format is a standard for allocating files in a partition. 
(Popular existing file formats are the FAT structure of DOS, 
NTFS structure of Windows NT, and the  HPFS structure of both OS/2 
and Windows NT.)
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