Red Hat ENTERPRISE LINUX 3 - INSTALLATION GUIDE FOR X86-ITANIUMTM-AMD64 AND INTEL EXTENDED MEMORY 64 TECHNOLO Installation Manual page 94

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Figure D-2. Disk Drive with a File System
As Figure D-2, implies, the order imposed by a file system involves some trade-offs:
A small percentage of the drive's available space is used to store file system-related data and can be
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considered as overhead.
A file system splits the remaining space into small, consistently-sized segments. For Linux, these
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segments are known as blocks.
Given that file systems make things like directories and files possible, these tradeoffs are usually seen
as a small price to pay.
It is also worth noting that there is no single, universal file system. As Figure D-3, shows, a disk drive
may have one of many different file systems written on it. As you might guess, different file systems
tend to be incompatible; that is, an operating system that supports one file system (or a handful of
related file system types) may not support another. This last statement is not a hard-and-fast rule,
however. For example, Red Hat Enterprise Linux supports a wide variety of file systems (including
many commonly used by other operating systems), making data interchange between different file
systems easy.
Figure D-3. Disk Drive with a Different File System
Of course, writing a file system to disk is only the beginning. The goal of this process is to actually
store and retrieve data. Let us take a look at our drive after some files have been written to it.
Figure D-4. Disk Drive with Data Written to It
As Figure D-4, shows, some of the previously-empty blocks are now holding data. However, by just
looking at this picture, we cannot determine exactly how many files reside on this drive. There may
only be one file or many, as all files use at least one block and some files use multiple blocks. Another
important point to note is that the used blocks do not have to form a contiguous region; used and
unused blocks may be interspersed. This is known as fragmentation. Fragmentation can play a part
when attempting to resize an existing partition.
As with most computer-related technologies, disk drives changed over time after their introduction. In
particular, they got bigger. Not larger in physical size, but bigger in their capacity to store information.
And, this additional capacity drove a fundamental change in the way disk drives were used.
1. Blocks really are consistently sized, unlike our illustrations. Keep in mind, also, that an average disk drive
contains thousands of blocks. But for the purposes of this discussion, please ignore these minor discrepancies.
Appendix D. An Introduction to Disk Partitions
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