O’Reilly Network: Understanding Unix Filesystems

“In last week’s article, we viewed a PC’s BIOS partition table
and its Unix partition table using the fdisk and disklabel
utilities. Let’s continue this week by looking at the newfs utility
and inode tables. The newfs utility actually formats your slice
with the filesystems you previously specified with the disklabel
utility. Let’s start by taking a closer look at formatting and
filesystems in general so we can gain a better appreciation of
newfs.”

“There are two types of hard-drive formatting. When you
purchased your hard drive, it most likely was already “low level”
formatted for you by the manufacturer. Low-level formatting creates
the tracks and sectors on the drive; the intersection of these
tracks and sectors creates the units of storage known as physical
blocks, which are 512 bytes in size.”

“The second type of formatting is called “high-level”
formatting. This type of formatting installs a particular file
system onto a slice of your physical drive using a utility such as
DOS’s format or FreeBSD’s newfs. Some examples of file systems are
FAT16, FAT32, NTFS, and FFS. Different file systems may vary in
performance, but they usually have two features in common:

• They require some type of table to map block addresses to the
  files contained within the blocks
• They may also use a “logical” block addressing scheme to try to
  optimize read/write performance”

“Let’s pretend you’re a file system for a moment.”

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