KarbosGuide.com. Module 6

About file systems: DOS formatting, FAT, etc.

The contents on this page:

  • What are file systems?
  • The file system and the OS
  • Limitations in disk size
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  • Previous page
  • We have seen before that the PC is a big data processor. We have also seen that data are bits and bytes, which are organized in files. One of the operating system's major tasks is to write these data to a disk. Hard, floppy, and zip disks must be formatted before we can save files on them. In these pages, we will review formatting, file systems, etc. We will start with a general view, then go in depth about FAT formatting, which is (still) the most common.

    What are file systems?

    As I wrote in module 4a, drives are storage media, which can hold a file system. When a disk is formatted in a drive, it becomes organized and prepared to receive data. When we format a disk, it receives a file system .

    Formatting can be compared to starting a library. You must install the book shelves and the catalogue system before any books are put in place. Once the library is ready, bring on the books! Similarly with a disk. When we format it, we "burn in" a file system to make it ready to receive data (files).

    We can format with any one of several different file systems:


    File Allocation Table is the original, old 16 bit DOS system is probably used in 90% of all PCs. It is also called FAT16 contrary to:


    This is a new addition to FAT, which Microsoft introduced with Windows 95 B the December -96 version (OSR2). The performance has been even improved with Windows 98.


    High Performance File System is from OS/2. It is an advanced 32 bit file system, which in all respects is far superior to FAT, except for possible usage. It can only be used with OS/2.

    NTFS from Windows NT

    A 32 bit file system like HPFS, but not compatible with it. NTFS can only be used in Windows NT/2000/XP. If it was available for use in Windows 95/98, it may be preferable to FAT and FAT32.


    NetWare is a server operating system from Novell. It has its own 32 bit file system. For that reason, the Novell server, contrary to NT or OS/2 servers, cannot be used as a work station. The file system is much faster than FAT, but it works only with Novell servers (typically file servers).

    ISO 9660

    This is for CDROMs and ISO 13346 for DVDs.


    Universal Disk Format is for big capacity disks like DVD RAM. UDF is not directly supported by older versions of Windows , you need a driver.


    UNIX servers have their own filing system. Here the use of upper/lower case in file naming is significant. Read in the following pages about the concepts of these file systems.

    Relationship between file system and operating system

    We see that that the file system is an integral part of the operating system. An operating system can sometimes work with different file systems:

    Operating system File system(s)
    DOS FAT16
    Windows 95/98 FAT16, FAT32
    Windows NT FAT16, NTFS
    Windows 2000/XP FAT16, FAT32, NTFS
    OS/2 FAT16, HPFS
    Novell NetWare proprietary file system

    The file system is actually the interface between operating system and drives. When the user software, such as MS Word, asks to read a file from the hard disk, the operating system (Windows 95/98 or NT) asks the file system (FAT or NTFS) to open the file:

    The file system knows where files are saved. It finds and reads the relevant sectors and delivers the data to the operating system.

    Limitations in disk size

    Over the years, the PC has suffered from a long list of irritating limitations. The hard disk industry has continuously developed hard disks with increasing capacity. However, the system software (BIOS, DOS, and FAT) has set its limitations:

  • DOS versions below 3.0 could only handle hard disks up to 16 MB.

  • Versions 3.0 to 3.32 could handle up to 32 MB.

  • DOS 4.0 could handle up to 128 MB.

  • DOS version 5.0 and the BIOS, which controls IDE drives, could only accept 1024 cylinders and disks up to 528 MB. This limit was broken with the EIDE standard.

  • FAT16 can handle a maximum of 2 GB because of 16 bit calculations of the cluster size.

  • FAT32 accepts disks up to 2048 GB. This standard will probably last another couple of years.

    Let us return to the file system in next page.

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    Learn more

    Read Windows tipswith a little about Windows 95/98.

    Read Module 6c about the relationship between BIOS, OS and hardware

    Read Module 7a about the videosystem

    Read about video cards in Module 7b .

    Read about digital sound in Module 7c .

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    Copyright (c) 1996-2005 by Michael B. Karbo. www.karbosguide.com.