Recording Formats; Dds-3 Recording Format; Dds Recording Format - Seagate STD124000N Product Manual

Introduction

Recording Formats

DDS-3 Recording Format

DDS-2 Recording Format

DDS Recording Format

Product Manual
The horizontal movement of the tape in combination with the angular movement of
the cylinder causes the track to be recorded diagonally across the tape rather than
straight down its length. The resulting recorded track, nearly one inch, is
approximately eight times longer than the width of the tape.
The Seagate Scorpion 24 DDS drive is designed to comply with the industry-
standard DDS-3, DDS-2, DDS-DC and DDS recording formats. These formats are
summarized in the following text.
The DDS-3 recording format provides for writing data in helical tracks that are the
same width as DDS-2. The significant capacity increase associated with DDS-3 is
achieved by: 1) doubling linear recording density from 61 Kbpi (DDS-2) to 122 Kbpi
along with the use of PRML encoding; 2) increasing tape length to 125 meters and
3) using the timing tracking system, which eliminates the need for dedicated top and
bottom servo burst information associated with the previous ATF system.
The DDS-2 or narrow track recording format provides for writing data in helical
tracks that are narrower than the previous DDS track width. This format doubles
capacity by increasing track density one and a half times, along with a 33% increase
in tape length; the higher output MP+ media associated with the 120-m DDS-2
cartridges ensures reliable data integrity given the decrease in track widths from
13.6 µm with DDS and DDS-DC to 9 µm with DDS-2.
This standard format was codeveloped by DDS manufacturers to support DAT
devices as computer peripherals. The objectives of DDS are to maximize storage
capacity and performance, facilitate data interchange, provide compatibility with
existing tape storage command sets and provide extremely fast random access.
The DDS format also takes advantage of the helical scan recording method and the
inherent error correction capability of the DAT technology to augment error detection
and correction.
The format consists of a finite sequence of data groups where each data group is a
fixed-length recording area. A data group is made up of 22 data frames and 1 ECC
frame; each frame is made up of two helical scan tracks. The advantages of the
fixed-length data group is that ECC is easily generated, and buffering requirements
are simplified. (See Chapter 6, "Tape Formats," for additional information.)
Although data groups are fixed-length and always contain 22 data frames, the DDS
format is designed such that variable-length computer records can be stored in the
fixed-length data groups.
Chapter 1
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