Advanced Intelligent Tape - AIT Technology

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Advanced Intelligent Tape (AIT) Technology
Sony produced the first AIT tape drive in 1996 with the goal of doubling capacity and transfer rate every
two years. AIT falls into the 8-mm category, and its cartridge is the same size as other 8-mm tape
cartridges, but its recording method is proprietary and incompatible with 8-mm products from Exabyte. AIT
drives include a cartridge-sensing system to ensure that only cartridges designed for AIT drives are used.
AIT AME media contains a special ID that the drive will recognize. If an AIT AME cartridge is mistakenly
inserted into a non-AIT 8mm drive, a write-protect feature will be activated to protect it from possible data
corruption.
The first-generation AIT format, the AIT-1, supported a native capacity of 25GB (65GB compressed with a
2.6:1 data compression ratio) and a 3 MB/sec native sustained transfer rate (7.8 MB/sec compressed). An

extended-length tape for the AIT-1 drive was later added to increase the maximum native capacity to
35GB (91GB compressed). An AIT-1 enhancement, dubbed the "Valueline" AIT-1, was introduced in
January 2001 and leverages elements of the AIT-2 design to increase the AIT-1 drive's native data
transfer rate to 4 MB/sec (10.4 MB/sec compressed). The Valueline AIT-1 also added an Ultra Wide SCSI
interface, a 10MB data buffer and increased the rotational speed of the drum to 6,400 RPM. It uses a
Partial Response Maximum Likelihood (PRML) data-encoding scheme to support its high linear recording
density of 116,000 bits per inch (bpi). The high compression rate is achieved using a customized and
optimized version of IBM's Adaptive Lossless Data Compression technology (ALDC), which delivers a
2.6:1 data compression ratio, although actual compression efficiency largely depends on data type.
AIT-1 uses a unique head geometry and tension control system which helps to reduce tape tension by as
much as 50 percent when compared with competing technologies. Tape tension is a critical factor in head
and media wear, and AIT's extremely low and carefully controlled tape tension results in a 50,000-hour
head life. Its Auto Tracking Following (ATF) servo system senses and corrects any off-track positioning,
keeping the tape perfectly centered on the read/write head for data accuracy.
Introduced in March 1999, the second-generation AIT drive, AIT-2, provides full backward compatibility
with AIT-1 while doubling the native capacity of the original AIT-1 drive to 50GB (130GB compressed).
The native data transfer rate was likewise doubled to 6 MB/sec (15.6 MB/sec compressed). This doubling
of capacity and speed was accomplished through technological advances in both the drive (recording
heads, channel coding, media formulation and mechanism design) and recording media. AIT-2 also has a
10MB data buffer and uses a Trellis-Coded Partial Response (TCPR) encoding method, which increases
its linear recording density to 167,000 bits per inch. The rotational speed of the AIT-2 drum was increased
from 4,800 RPM to 6,400 RPM. AIT-2 uses Sony's patented HyperMetal laminate heads and an on-drum
amplifier to enhance the signal to the head and reduce noise, thereby minimizing read errors.
AIT drives use an Advanced Metal Evaporated (AME) tape media, which reduces the accumulation of
deposits on the head. AME media is made without nonmagnetic binder materials that can contaminate the
read/write heads or produce other media-related drive errors. AME's Diamond-Like Carbon (DLC)
abrasive resistant coating limits wear on the head and media and eliminates the need for cleaning tapes.
The head itself detects any accumulation of deposits on the head from changes in error rates. When the
head detects deposits, it automatically initiates a self-cleaning process using the built-in head cleaner,
thus eliminating the need to clean the head regularly using a cleaning cartridge.
AIT's key differentiating feature is intelligence embedded into the tape cartridge called Memory-In-
Cassette (MIC). Sony's MIC technology was introduced with the first-generation AIT-1 drive and later
enhanced in the AIT-1 extended-length tape model and on AIT-2. MIC is a 64Kb flash memory chip (16Kb
on SDX1-25C tape media) that is incorporated into the data cartridge and stores various system and user
information directly within the MIC structure to enhance data reliability, error prediction and access
performance. On-chip data includes system logs, search map and user-definable information, allowing
fast access to data anywhere on the tape. Storing key data parameters in nonvolatile memory that is an
integral part of the cartridge rather than on the tape media provides fast access to on-tape structures and
media statistics by any MIC-compatible AIT drive without having to first read the physical tape media. The
MIC detects ID data for the requested information and moves the tape at its rewind speed (122
inches/second on AIT-1 and 160 inches/second on AIT-2) to the approximate location of the data. Then it
slows down to read the ID blocks on the tape to locate the specific data requested. AIT supports an
average data access time of 27 seconds (using a 170m tape), which is more than 2x improvement when
compared with competing technologies. Other tape technologies maintain directory information in a
header area on the tape media itself that must be read each time a tape is loaded and rewritten when any
modifications to data are made. The MIC also supports multiple partitions and load points, which allows

the loading and unloading of a cartridge to occur without having to rewind the tape to the beginning. The
ability to park the tape at any one of the 64 on-tape partitions means that an AIT drive can support a
"midpoint load" (similar to the StorageTek 9840), which would essentially halve the search time to the end
of tape in either direction, resulting in fast data access speeds during restore operations. This assumes
that before unloading a cartridge from the drive, the tape was positioned to its midpoint location for future
use.
Sony's third-generation AIT product, the AIT-3, was made available for sale in November 2001. The AIT-3
doubles the capacity and performance of AIT-2 and is fully backward read and write compatible with all
AIT-2 and AIT-1 media, enabling users to seamlessly migrate to the higher capacity of AIT-3 without
losing access to previously backed-up data. A new 230-meter data cartridge, the SDX3-100C, has been
designed for use with the AIT-3. AIT-3 supports a native capacity of 100GB (260GB with 2.6:1 data
compression) and a native data transfer rate of 12 MB/sec (31.2 MB/sec compressed). The increased
capacity of AIT-3 was achieved by narrowing the track pitch from 11 microns on AIT-1 and AIT-2 to 5.5
microns on AIT-3. The increase in data transfer rate results from a number of factors, including doubling
the number of channels (from two to four), doubling the number of heads (from four to eight),
simultaneously utilizing two recording heads on tape, and the increased area density. The data buffer has
also been increased from 10MB on AIT-1 and AIT-2 to 18MB on AIT-3.
Like the AIT-1 and AIT-2, the AIT-3 is designed in a 3.5-inch form factor. AIT-3 supports an Ultra 160
Wide SCSI LVD/SE interface, allowing it to support up to a 160 MB/sec synchronous burst data transfer
rate, whereas AIT-1 and AIT-2 both use an Ultra Wide SCSI LVD/SE interface with a maximum
synchronous burst data transfer rate of 40 MB/sec. AIT-3 drives incorporate Sony's new Remote-Memory-
In-Cassette (R-MIC) media interface system. The R-MIC enables the drive to access key tape parameters
embedded in the data cartridge without the tape being loaded, improving access time to data. This is a
particularly useful feature for tape automation applications.
Sony continues to maintain its commitment to the AIT roadmap and its design goal of doubling both
capacity and performance every two years for six generations. In doing so, it has provided general
visibility for AIT-4, AIT-5 and AIT-6 capacity and performance, which is in keeping with its design goal.