1975	DEC RL01
	First sector servo positioning system

Why it’s important Embedding servo information, that is, intermixing user data sectors with position information sectors, increased the usable capacity per disk drive. For removable media drives the complex and costly head alignment tools and maintenance were also eliminated. Ultimately, all disk drives adopted this technology.

Discussion
Fred Hertrich was contracted by DEC to develop the concepts for a low maintenance embedded servo successor to the RK05 cartridge disk drive that had utilized the IBM 2315 cartridge. The major challenge was to develop a servo technology that had no secondary transducer, i.e. all velocity and position servo information when seeking or track following would be obtained from the embedded servo bursts. The RL01 was introduced at 5 Mbytes formatted capacity with the IBM 5440 type top loading cartridge which had significant reliability advantages to the 2315 type. An upgrade to 10 Mbytes was introduced about 2 years later, compatible with the installed base of RL01's and its controllers.

The RL series was produced in Colorado Springs and Kaufbeuren, Germany.

Sector servo technology for disk drives was first patented by IBM's Robert Sippel in 1961, see US patent 3,185,972, but not introduced in any IBM product until much later (circa 1990). However, this patent required secondary transducers to keep track of position data when seeking.

Additional information
Lower maintenance costs and higher reliability than previous generations of cartridge drives were two of the major goals for the program. DEC had shipped approximately 100,000 of the RK05 drives that utilized a cartridge mechanically compatible to the IBM 2315, which had the advantage of being a front loader. The problems with the 2315 design were numerous and IBM dropped it in favor of the 5440 style after one product. DEC likewise followed suit and chose the top load 5440 plastics for its far superior mechanical and media protection properties.

However, since drives of this era required careful head alignment procedures and special track alignment reference media, this area remained a source of significant support costs and interchange incompatibility. Thus, the primary technology imperative was to develop a track following system that obviated the need for head alignment and guaranteed cartridge data interchange. It was also realized that ultimately all disk drives would require data track following so developing the technology first would create a competitive advantage. This goal was achieved with an embedded track following servo that utilized pre-recorded servo information between data sectors. (All DEC drives had a fixed block size architecture). Additional reliability/low maintenance cost features for the RL01/02 included a recirculating air system to substantially extend the life of the HEPA filter and universal spindle and power supplies so there was only one model for worldwide installation. A custom fan assembly also enabled the drive to set a new standard for in office audio noise levels from a 14" disk drive.

The initial concepts were developed by Hertrich Consulting, which was under exclusive contract to DEC. Fred Hertrich provided much of the detailed initial design and was assisted by Dick Laatt (sp?) for the data channel. Pete McLean from DEC designed the controller for the PDP-11. DEC was growing rapidly at the time and the storage business even faster, requiring new manufacturing facilities around the world. Grant Saviers from Engineering and Dave Brown from Manufacturing convinced Ken Olsen, after a lengthy debate, to locate Manufacturing and Engineering in Colorado. This would be DEC's first (and only) major engineering facility more than a short drive from Ken's office in Maynard, MA. Initial production of the RL series began in a leased ex mobile home factory in Fountain, CO. Dave & Grant selected the 330 acre Rockrimmon site and commenced construction of a major facility for the design and manufacturing of disk drives, disk subsystems, and later cluster controllers. The site grew to about 1 million square feet of facilities before DEC cratered in the 1990's.

Anecdote: The Rockrimmon site was zoned residential and Colorado Springs was anxious enough to become "Silicon Mountain" that it rezoned the site providing DEC made some site improvements. Thus, DEC built its first and only railroad bridge for the frequent coal trains to the Pueblo power plant. Sometimes, "you do what you gotta do". This site was far and away one of the most spectacular manufacturing sites in the USA, with a panoramic view of Pikes Peak.

Provenance note: This article was written by G Saviers. Version 11 of this article was reviewed and approved by the Computer History Museum's Storage SIG on June 20, 2012.