

            NOVELL TECHNICAL INFORMATION DOCUMENT

TITLE:             FDISK and Cluster Sizes
DOCUMENT ID:       TID021696
DOCUMENT REVISION: A
DATE:              03AUG94
ALERT STATUS:      Yellow
README FOR:        NA

NOVELL PRODUCT and VERSION:
Novell DOS 7

ABSTRACT:

FDISK and Cluster Sizes

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ISSUE

The cluster (or file allocation unit) is the smallest amount of disk space 
DOS can assign to a file. Partial clusters cannot be given to a file, nor 
can two different files occupy space within the same cluster.  As a result, 
there will always be some degree of unusable space on a disk.

Statistically, the average file will "waste" about half of a cluster.  
Therefore, a large number of small files will waste much more space than a 
small number of large files. It is desirable to have very small clusters, in 
order to minimize the wasted space.

You can control cluster size by strategically choosing the size of your 
partitions or logical drives (from this point, this document will use the 
term "partition" to refer to both partitions and logical drives).  Partitions 
and are created and deleted with the utility FDISK.COM. Note that the process 
of deleting a partition will destroy all information contained within.

The following table shows the cluster sizes that correspond to various 
partition sizes.

PARTITION SIZE         FAT SIZE   SECTORS/CLUSTER  CLUSTER SIZE
--------------         --------   ---------------  ------------
up to 15.9Mb           12 bit           8              4K
16 - 127.9Mb           16 bit           4              2K
128 - 255.9Mb          16 bit           8              4K
256 - 511.9Mb          16 bit          16              8K
512 - 1023.9Mb         16 bit          32             16K
1024Mb - 2Gb           16 bit          64             32K

It is theoretically possible for FAT size and cluster size to vary from this 
table. For example, it is possible for a partition up to 8Mb in size to have 
12 bit FAT and 2K clusters, which would give more efficient usage of space. 
However, Novell DOS 7, DR DOS 6.0, and MS DOS 6.x all use the implementation 
listed in this table.

Some DOS versions earlier than 4.x may vary from this table. Also, it is 
possible that some 3rd party partitioning utilities may not follow this 
implementation. If you are not sure what utility was used to create your DOS 


partitions, you may wish to check your actually cluster size by using Novell 
DOS 7 CHKDSK.EXE, which will list the number of "bytes in allocation unit". 
You can also use 3rd party utilities such as Norton's SYSINFO.EXE.

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