TITLE
    Mac OS Extended Format: Volume and File Limits
Article ID:
Created:
Modified: 		24601
9/9/98
8/15/00
TOPIC

    What are the limits of file and volume sizes in Mac OS Extended Format (sometimes referred to as HFS Plus)? What is the maximum number of files on a volume?

DISCUSSION

    The following table provides detailed information on Mac OS Extended Format volume and file limits.
    Mac OS Extended Format: Volume and File Limits
    Maximum number of volumes
    21 (2)
    Maximum volume size
    2 terabytes
    Maximum file size
    2 terabytes (3)
    Maximum data fork size
    2 terabytes (4)
    Maximum resource fork size
    16 megabytes (5)
    Maximum number of files
    more than 2 billion (1)
    Maximum number of files/folders in a
    folder
    32,767

    Notes:

    1) The actual number of files that can be stored on an HFS Plus volume depends on the size of the volume and the size files. For example, a 4 GB HFS Plus volume with the default block size of 4K, will have one million available blocks. Thus the volume could hold up to a million small files or fewer larger ones. A larger volume with the same default block size could hold proportionately more files.

    2) At system boot, the event queue for the Finder can accept 20 volumes plus the startup volume. Once the computer has completed the boot process, you may use a disk utility to mount as many additional volumes as there are available file control blocks. This number is variable depending upon how many applications are running, files open, or other operating system processes which require file control blocks.

    3) Under Mac OS 9. Mac OS 8.x only supports file sizes of up to 2 GB in size.

    4) Mac OS 9 with Mac OS Extended savvy applications can access a fork this size. Mac OS 8.x and Mac OS 9 with applications using the standard HFS APIs can access forks up to 2 GB in size. It not possible to access any data in a fork larger than 2 GB without using the Mac OS Extended APIs.

    5) This limit is imposed by the Resource Manager.


    For definitions of some of these terms, and for information about Mac OS Standard Format (HFS), please see the following Knowledge Base article: Article 8647: " Macintosh: File System Specifications & Terms "

    For more information on Mac OS Extended Format , please see the following Knowledge Base article:
    Article 30344: " Mac OS 8.1: About Mac OS 8.1 Extended Format "

Document Information
Product Area: Mac OS System Software
Category: General OS
Sub Category: General Topics

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