Messages in this thread |  | | Date | Tue, 30 Jul 1996 20:13:58 +0800 | From | Bruce Murphy <> | Subject | Re: Microsoft FAT 32. |
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Hello, I wasn't sure if you had seen this, btu I thought that I should pass it on anyway. Mike might find it interesting.
> >This very interesting Article is about the 32-Bit File System that is > >being developed by Microsoft at the moment:
> >Market Bulletin > >Windows Product Team, May 1996
> >The FAT32 File System
> >This market bulletin is intended to help customers understand > >Microsoft's FAT32 file system for Windows 95, which is due to start > >shipping with new PC's equipped with Windows 95 in the fall of 1996.
> >The existing File Allocation Table (FAT) file system was invented in > >1977 as a way to store data on floppy disks for Microsoft Stand-alone > >Disk Basic. Although originally intended for floppy disks, FAT has > >since been modified to be a fast, and flexible system for managing > >data on both removable and fixed media.
> >A new generation of very large hard disks will soon be shipping, and > >the existing FAT data structures have finally reached the limit of > >their ability to support ever larger media. FAT currently can support > >a single disk volume up to 2 Gigabytes in size. FAT32 is an > >enhancement of the FAT file system that supports larger hard drives > >with improved disk space efficiency.
> >FEATURES > >FAT32 provides the following enhancements over previous > >implementations of the FAT file system: - Supports drives up to 2 > >Terabytes in size. - Uses space more efficiently. FAT 32 uses smaller > >clusters (e.g. 4kb clusters for drives up to 8GB in size), resulting > >in 10 to 15% more efficient use of disk space relative to large FAT > >drives. - More robust. FAT32 has the ability to relocate the root > >directory and use the backup copy of the FAT instead of the default > >copy. In addition, the boot record on FAT32 drives has been expanded > >to include a backup of critical data structures. This means that FAT32 > >drives are less susceptible to a single point of failure than existing > >FAT volumes. - More flexible. The root directory on a FAT32 drive is > >now an ordinary cluster chain, so it can be arbitrarily large and > >located anywhere on the drive. In addition, FAT mirroring can be > >disabled, allowing a copy of the FAT other than the first one to be > >active. These features allow for dynamic resizing of FAT32 partitions. > >Note, however, that while the FAT32 design allows for this capability, > >it will not be implemented by Microsoft in the initial release.
> >COMPATIBILITY CONSIDERATIONS > >In order to maintain the greatest compatibility possible with existing > >applications, networks and device drivers, FAT32 was implemented with > >as little change as possible to Windows 95's existing architecture, > >internal data structures, Application Programming Interfaces (APIs) > >and on-disk format. However, because 4 bytes are now required to store > >cluster values, many internal and on-disk data structures and > >published APIs have been revised and/or expanded. In some cases, > >existing APIs will fail on FAT32 drives. Most applications will be > >unaffected by these changes. Existing utilities and drivers should > >continue to work on FAT32 drives. However, MS-DOS block device drivers > >(e.g. ASPIDISK.SYS) and disk utilities for these will need to be > >revised to support FAT32 drives.
> >All of Microsoft's bundled disk utilities (Format, FDISK, Defrag, > >MS-DOS and Windows ScanDisk, and DriveSpace) have been revised to work > >with FAT32. In addition, Microsoft is working with leading device > >driver and disk utility vendors to support them in revising their > >products to support FAT32.
> >PERFORMANCE > >For most users, FAT32 will have a negligible performance impact. Some > >applications may see a slight performance gain from FAT32. In other > >applications, particularly those heavily dependent on large sequential > >write operations, FAT32 may result in a modest performance > >degradation. The overall effect on raw disk performance is less than > >5% however, and the overall impact on application performance as > >measured by WinStone is typically less than 1%.
> >DUAL-BOOT PERSONAL COMPUTERS > >At this time, Windows 95 OEM Service Release 2 is the only operating > >system capable of accessing FAT32 volumes. Windows 3.1, MS-DOS and the > >original version of Windows 95 will not recognize FAT32 partitions, > >and thus they are unable to boot from a FAT32 volume. Microsoft's > >plans for supporting FAT32 in Windows NT are still being determined, > >but at this time, Windows NT is unable to access, or dual boot from, > >FAT32 volumes. At minimum, Microsoft will provide a utility to convert > >a FAT32 volume to an NTFS volume.
> >Customers who run Windows 95 in real mode (for example, to run a game) > >will be able to use FAT32 volumes, however.
> >CREATING FAT32 DRIVES > >In OEM Service Release 2, if you run the FDISK utility on a system > >with a drive over 512MB, it will ask whether to enable large disk > >support. If you answer yes, any partition you create that's greater > >than 512MB will be marked as a FAT32 partition.
> >WHY NOT JUST ADD NTFS TO WINDOWS 95? > >NTFS is an advanced file system, with support for many features not > >present in FAT32, including per-file compression, security and > >transactioning. It is not feasible to implement NTFS within the memory > >and compatibility constraints of the Windows 95 platform. Windows 95 > >still supports real-mode MS-DOS for booting and running some MS-DOS > >based games. Adding NTFS support to the MS-DOS kernel would have > >required a significant amount of MS-DOS memory, and thus would have > >precluded the use of many MS-DOS mode games and applications. > >Protect-mode only support for NTFS would not have allowed Windows to > >boot from an NTFS volume.
> >TECHNICAL IMPLEMENTATION > >Because of the compatibility considerations described above, the > >implementation of FAT32 involved very little change to Windows 95. The > >major differences between FAT32 and earlier implementations of FAT are > >as follows: - Two new partition types are defined: 0xB and 0xC. Both > >indicate FAT32 volumes; type 0xC indicates a FAT32 partition that > >requires Extended Int13h support (LBA). - The boot record on FAT32 > >drives requires 2 sectors (due to expansion and addition of fields > >within the BPB). As a result, the number of reserved sectors on FAT32 > >drives is higher than on FAT16, typically 32. This expanded reserved > >area allows two complete copies of the boot record to be stored there, > >as well as a sector in which the free space count and other file > >system information is stored. - The FAT is now larger, because each > >entry now takes up 4 bytes and there are typically many more clusters > >than on FAT16 drives. - The root directory is no longer stored in a > >fixed location. A pointer to the starting cluster of the root > >directory is stored in the extended BPB. - The on-disk format for > >directory entries is unchanged, except that the two bytes previously > >Reserved for Extended Attributes now contain the high order word of > >the starting cluster number. - MS-DOS APIs that rely on intimate > >knowledge of the file system layout generally fail on FAT32 drives. > >For instance, GetDPB (Int 21h, function 32h), Int 25/26h Absolute Disk > >Read/Write, and most of the Int 21h, function 440Dh IOCTLs will fail > >on FAT32 drives. New forms of these APIs are provided in OEM Service > >Release 2 which work on all FAT drives. - Win32 APIs are not affected > >by FAT32, with the exception of one additional API called > >GetFreeSpaceEx() for determining the true free space on a FAT32 > >volume.
-- Packrat (BSc/BE;COSO;Wombat Implementor) Nihil illegitemi carborvndvm.
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