User Guide

Ampex 1308911-02 3-3
DD-2 Tape Format DD-2 Format Types
• Fully formatted (or preformatted).
Initialized (or non-preformatted) is the simplest kind of formatting. This is a relatively quick
operation (about 20 seconds). Initializing records some Volume Format Information at the
beginning of tape and leaves the remaining tape unrecorded. An initialized tape allows only
for a single partition of data; that is, the volume cannot be sub-divided into smaller volumes
on the cartridge.
In partial formatting (also called partial preformatting), part of the tape is formatted and the
remaining part is treated as a single initialized partition. This type of formatting is often used
to create one or more small partitions at the beginning of the tape and a large partition for data
at the end. It may be useful in some applications to use the small partitions at the beginning of
the tape for directory or other descriptive information about the data in the large partition.
In full formatting (also called preformatting), the tape is written at several times normal play
speed with information that defines all the partitions on the tape. Full formatting allows for
multiple partitions and provides the most flexibility in partitioning data on the cartridge. Of
the three types of formatting, full formatting takes the longest time to complete.
3.4.1 System Zones
System zones are areas that allow tape loading and unloading at locations other than BOT.
Their layout is specified at the time the tape is formatted.
System zones can be located anywhere and do not necessarily correspond to partition
boundaries unless the tape was specifically formatted with system zones at partition
boundaries.
Although system zone placement can affect data access times and space usage, they are
transparent to applications and do not affect the logical structure shown in Figure 3-1.
3.4.2 Partitions
Formatting a DD-2 tape creates one or more partitions. Each partition contains a set number
of physical blocks (also referred to as double frames). These are the smallest units (1,199,840
bytes) that the drive can use to write data to tape. Typically, each physical block contains
multiple data blocks which are the units in which your application transfers data to or from the
tape drive (8192 bytes is the default data block size).
Each partition comprises a separate entity, logically as well as physically. Most operations,
including read and write, cannot cross a partition boundary. Only explicit partition positioning
commands and a rewind immediately after cartridge load will cross a partition boundary.