Monday, August 4, 2014

As the Bubbl Bursts

The invention of magnetic bubble memory was once seen as a revolutionary computer development - the wave of the future. It is now a nearly forgotten technology.
"Many persons expect that the most dramatic changes in digital systems will result from magnetic-bubble chips that could well hold a million or more bits in the not-too-distant future. Along with charge-coupled devices, these memories show promise of replacing magnetic tape and disks for small systems." [emphasis in the original]
- Understanding Digital Electronics, Texas Instruments, 1978
One of the more unusual computer objects that I've collected over the years uses this memory. It is called the QSB-11A Bubbl-Board. I was told by the person that sold it to me that it had been used in a system at Los Alamos National Laboratory. I have no idea how it was used. Given the nuclear research conducted there I sometimes wonder if I should check to see if it is "hot."

Magnetic bubble memory module

It contains 1 megabit of non-volatile, solid-state memory utilizing magnetic domains that are referred to as "bubbles." The Wikipedia article provides a good overview of the history of this invention and how it works.

This circuit board was manufactured by a company called Bubbl-tec in the early 1980s. I find the excessive use of the spelling "Bubbl" and the silly font endearing... Bonus points for the copious use of hyphenated trademark names.

Bubbl-Board logo
The Bubbl-Board
Bubbl-tec logo
By Bubbl-tec

It was designed for use in systems made by Digital Equipment Corporation (DEC) that use the Q-bus for peripheral interfacing, such as the pdp LSI-11 or the MicroVAX. The QSB occupies a standard dual-height I/O slot. The computer accesses the memory on the board as if it were stored on an 8" floppy diskette. The storage format is similar to that used by the DEC RX01 or IBM 3740 drives.

QSB-11A Bubbl-Board

The micro-controller on the Bubbl-Board is a Zilog Z80A with 256 bytes of RAM and a firmware ROM. This is used to emulate a DEC RXV11 Q-bus interface connected to a single RX drive. The standard DEC device drivers address sectors and tracks that the board maps to the major tracks and minor loops of the bubble memory subsystem. This "virtual floppy" is organized as 26 sectors and 39 tracks, storing 128 bytes of user data per sector. The usable storage is about one half of a real RX01 diskette.

There's a fascinating article on the invention called Bubbles: the better memory which describes the origin of the technology. It was part of a series by EE Times called The Centurey of the Engineer: Misunderstood Milestones. It also gives some insight into what the press inevitably called the "The Computer Bubble that Burst." The latter article was written the same year as the copyright date on this printed circuit board. It was considered nearly obsolete before it was even sold.


  1. I remember the hype about bubble memory. But thing was CCD won out.

    1. IBM has recently been working on an experimental technology that they they call racetrack memory. The magnetic domain walls at the heart of these devices are similar in concept to bubble memory. Maybe there's still hope that it will live up to the hype! Some day...