3. Helical Scan Technology Helical scan was invented in 1961 and developed for the video recording industry. In the design of helical scan products the write and read heads are mounted on a drum that rotates at high speed. The head is mounted at a slight angle to the tape path, causing the recording of data on diagonal stripes across the tape. This enables higher track and linear bit densities compared to longitudinal methods. The first 8mm storage device based on this technology was introduced in 1987 by Exabyte (EXB-8200). Due to it's high capacity of 2.3 GB per cartridge and low cost, the exabyte became the de facto standard in workstation/mid range system backup. Now the 8mm Mammoth offers a low-cost storage capacity of 20Gb with a data transfer rate of 3MB per second. Exabyte's latest release Mammoth-2 offers 60GB of data storage with a data transfer rate of 12MB per second. The introduction of Smartclean (self-cleaning tape cartridge), AME (Advanced Metal Evaporation) data cartridges, a 32MB adaptive data buffer and a base price of £3,000 enables Exabyte to position itself in the mid-range backup market. This, and other high capacity Helical-Scan technologies are further described in table 2. The DAT (Digital Audio Tape), pioneered by Sony, is a 4mm data cartridge which offers a cost-effective means of backup. The latest 4mm backup drive DDS-4 offers 40GB of storage at a data transfer speed of 4.8Mb per second (17GB per hour). The drive comes standard with a 8MB buffer. A DDS-4 drive costs about £1,500. This drive is specifically aimed at higher volume backups (e.g. network). DDS-4 is downwardly read compatible with DDS-3, DDS-2 and DDS-1 formats. Table 2 : Helical Scan Technology Media Storage Capacity (GB) Transfer Rate (MB/s) Price Band (GBP) DAT - DDS1 2 0.4 <5K DAT - DDS2 4 0.8 <5K DAT - DDS3 12 2 <5K DAT - DDS4 40 4.8 <5K Exabyte 2.3/5/7 0.2/1 <5K Exabyte - Mammoth 20 3 <5K Exabyte - Mammoth II 60 12 <5K Sony AIT - 1 25/35 3 <5K Sony AIT - 2 50 3 <5K Metrum 14 4 10-20K D1 40/100 16/32 30-40K Original D2 25/75/165 15 80-100K DD - 2 50/150/330 15 80-100K Redwood (D3) 10/25/50 11.25 80-100K DTF - 1 42 12 40-50K DTF - 2 200 24 80-100K In 1992 Ampex released a line of data storage products based on the 19mm D2 cartridge. This had been successfully used in the broadcast industry and was now re-engineered for data storage. Three capacities where available: 25GB, 75GB and 165GB, the form factor of the cartridge increasing in size respectively, but all used in the same drive. Drives are manufactured by Ampex, and automated library systems are available from Ampex and EMASS. As the first of the high capacity cartridge drives to become available, they have been used by a small number of oil companies for their data archive. The drives delivered high data transfer rates 15 MB per second. The 19mm tape format includes a linear track that contains information allowing the impressive search rate of 800Mb per second. Ampex are currently marketing double capacity DD-2, giving a 330GB cartridge with a data transfer rate of up to 20MB per second. D3 was first used commercially in broadcasting at the 1992 Summer Olympic Games in Barcelona, Spain. StorageTek have since adapted this new generation of D3 video recording technology to the data processing industry. The product is termed RedWood. The D3 device records at a 20-degree angle to the edge of the tape. The result of this is much longer tracks. Higher capacities are possible as helical-scan recording suffers from none of the manufacturing tolerance and track density limitations of fixed head devices. The tape is able to move at slower speed, hence less stress on the tape. Redwood is currently no longer actively marketed by StorageTek. The D3 media is a standard 3480 form factor. The media is a Metal Particular (MP+) media specially developed to match hardware components of RedWood. It is reported to give at least 50 times more durability than earlier helical technology. This is mainly due to reduction in mechanical tension. Current native media sizes available are 10Gb, 25Gb and 50Gb where the tape is the same thickness, the only difference being the length of tape on the spool. The drive itself has a native read/write transfer rate of 11Mb/second and a 50Gb tape can be fully searched in 90 seconds. D3 was beta-tested in the US at Mobil Exploration and Production Technical Centre in Dallas, Texas. The platforms used were RS/6000 and Cray. The test application was the processing, archival and migration of seismic data. Several contractors are reported to be using Redwood for data acquisition. It is of note that although Redwood is currently supported in a maintenance-mode it is no longer actively marketed by StorageTek. AIT (Advanced Intelligent Tape) is the latest 8mm drive technology from Sony. It currently offers the capacity of 50GB with a data transfer rate of 3MB per second. The initial cost of the drive is about £3,500. It is not compatible with other 8mm drives; however it does offer a 16Kbit EEPROM termed Memory in Cassette (MIC). This can store index information for increased access. Sony do have an impressive roadmap for the further development of AIT products. Sony like Ampex have also produced formats specifically for the entertainment industry and then converted the technology for use in mass data storage projects. DTF format is based on Sony's digital Betacam recording technology. DTF-2 is capable of high speed data transfer rates of up to 24 MB per second, a fibre channel interface drive subsystem is also available. Sony have defined a clear roadmap for DTF, development is currently underway on a 400Gbdrive with a 48MB per second data transfer rate. Table of Contents Introduction Longitudinal Recording Technology Helical Scan Technology Optical Technology Summary The Future See other technical papers.