World Library  
Flag as Inappropriate
Email this Article


Article Id: WHEBN0006502190
Reproduction Date:

Title: Rk05  
Author: World Heritage Encyclopedia
Language: English
Subject: Digital Equipment Corporation, PDP-11
Publisher: World Heritage Encyclopedia


An RK05 drive with a mounted RT-11 disk pack.

The RK05 DECpack was a moving head magnetic disk drive manufactured by the Digital Equipment Corporation of Maynard, Massachusetts. It stored approximately 2.5 MB on a 14", single-platter IBM-2315-style front-loading removable disk cartridge. The cartridge permitted users to have relatively unlimited off-line storage and to have very fast access to such data. At the time DEC had numerous operating systems for each computer architecture so operating systems could also be changed quickly. The RK05 was the disk successor to DECtape for personal, portable, and expandable storage. While the smallest practical configuration was two drives, many systems had four or more drives.

Drive head mechanism on an RK05 disk drive from Digital Equipment Corporation.

Occupying 10.5 inches (6U) of space in a standard 19-inch rack, the drive was competitive at the time. The cartridge contained a single, 14" aluminum platter coated with iron oxide in an epoxy binder. The two ferrite and ceramic read/write heads were pressed towards the disk by spring arms, floating on an air bearing maintained by the rotation of the disk. They were positioned by a voice coil actuator using a linear optical encoder for feedback. The track density was 100 tracks-per-inch. The bit density along the track was about 2200 bits-per-inch. Discrete electronics computed the velocity profile for seeks commanded by the controller. An absolute filter (HEPA filter) provided pressurized air to the cartridge, excluding most contaminants that would otherwise cause head crashes.

When used on 16-bit systems such as the PDP-11, the drive stored roughly 1.2 megawords. When used on 12-bit systems such as the PDP-8, the drive stored 1.6 megawords (so roughly the same bit capacity, albeit formatted differently). Multiple drives were daisy chained from their controller using Unibus cabling; a terminator was installed in the farthest drive.

The 16-bit (Unibus) controller was known as the RK11; it allowed the connection of up to eight RK05 drives. Seeks could be overlapped among the drives but only one drive at a time could transfer data.

The most-common 12-bit (Omnibus) controller was known as the RK8E; it supported up to four RK05 drives. The RK05 disk had more than 4096 sectors and so could not be addressed completely by a single PDP-8 12-bit word. To accommodate this, the OS/8 operating system split each drive into two logical volumes, for example, RKA0 and RKB0, representing the outermost and innermost cylinders of the drive.


  • The RK05E was a late version of the standard-density RK05 drive. It contained many reliability enhancements compared to the earlier versions.
  • The RK05J was the final version of the standard-density RK05 removable pack drive.
  • An non-removable RK05F was also produced. By "fixing" the otherwise removable cartridge in place, it was able to avoid the cartridge-to-cartridge compatibility problems that limited the capacity of the ordinary RK05. As a result, it could operate at twice the normal track density, doubling the capacity of the drive to about 5MB.
  • Prior to the introduction of DEC's own drives, DEC resold two drives from Diablo Data Systems (later acquired by Xerox). Known as the RK02 (very few shipped) and RK03 (Diablo Model 31), these were interface compatible with the RK05; RK03 and RK05 disks could be interchanged as well.

External links

  • RK05 drive information compiled by David Gesswein
This article was sourced from Creative Commons Attribution-ShareAlike License; additional terms may apply. World Heritage Encyclopedia content is assembled from numerous content providers, Open Access Publishing, and in compliance with The Fair Access to Science and Technology Research Act (FASTR), Wikimedia Foundation, Inc., Public Library of Science, The Encyclopedia of Life, Open Book Publishers (OBP), PubMed, U.S. National Library of Medicine, National Center for Biotechnology Information, U.S. National Library of Medicine, National Institutes of Health (NIH), U.S. Department of Health & Human Services, and, which sources content from all federal, state, local, tribal, and territorial government publication portals (.gov, .mil, .edu). Funding for and content contributors is made possible from the U.S. Congress, E-Government Act of 2002.
Crowd sourced content that is contributed to World Heritage Encyclopedia is peer reviewed and edited by our editorial staff to ensure quality scholarly research articles.
By using this site, you agree to the Terms of Use and Privacy Policy. World Heritage Encyclopedia™ is a registered trademark of the World Public Library Association, a non-profit organization.

Copyright © World Library Foundation. All rights reserved. eBooks from Project Gutenberg are sponsored by the World Library Foundation,
a 501c(4) Member's Support Non-Profit Organization, and is NOT affiliated with any governmental agency or department.