ERNIE in Detail
ERNIE in Detail
ERNIE Mark I was the first large-scale use by the Post Office of transistors, rectangular-hysteresis-loop ferrites and printed circuit board techniques.

Photo: ERNIE Mk 1 showing the rear view of the double-sided equipment racks.
| EXIT | ERNIE | Random Numbers | The Works | Acknowledgements |

ERNIE is fitted onto five double-sided Post Office telephones racks which are bolted together and mounted on a plinth. Prior to 1960, Post Office equipment racks were painted 'battleship grey'.

This extract from a research document from 1958 explains the principle:

"The machine which has been designed to generate the list of random numbers for the monthly draws of Premium Bonds is known as the Electronic Random Number Indicator Equipment or ERNIE. It uses the random voltages generated at the terminals of cold-cathode tubes as its primary source of random events, two such sources contributing to each character of the nine-digit number provided by the machine. The complexity of the machine arises from the need to avoid any correlation between the digits of each number or between the numbers themselves. The high degree of reliability demanded of the machine and the speed of operation required of its counters is such that special core/transistor circuits had to be introduced on a fairly large scale although other parts of the machine use more conventional techniques. The output of the machine is fed to page printing teleprinters since although ERNIE can operate at much higher speeds than those required for teleprinting, no other suitable printer is commercially available in sufficient quantity at an economic price and with the same reliability."

Random Numbers
Random Numbers
Random Numbers:

"Generating genuinely random numbers using a computer is harder than you might think. Computers follow rules and are therefore predictable. Computer software can only mimic unpredicatability; eventually patterns will emerge.

ERNIE 1 generates random numbers from a physical event - the random movement of electrons through neon gas. Subsequent ERNIE machines have continued to use an unpredicatable physical event, rather than computer software, to generate the true random numbers needed to pick winning Premium Bonds.

Today the generation of random numbers is important for many everyday computational activities. These include simulating real physical processes such as the weather or financial markets, encrypting secure transactions over the internet and creating chance in computer games." [BT Heritage]

Photo: ERNIE display at the Science Museum, London © LSA  March 2010. The light grey rectangular box is one of the random number generators.
Demo model of ERNIE

"Dr Charles Hill, Postmaster General, using  a demonstration model of ERNIE 1 on 6th February 1957. The team developed this electronic, non-transistorised demonstration model to explain to the press and public how a random number would be generated. Meanwhile they worked hard to deliver the technically innovative ERNIE 1 in time for the first draw." [BT Heritage]

Photo: ERNIE display at the Science Museum.
The Works
The Works
A detailed look at some of the equipment.

Photo: ERNIE racking on display at the Science Museum, London © LSA  March 2010.

Disclaimer: These pages are an unofficial review of ERNIE and Premium Bonds. Photos copyright Light Straw Archives, as marked. Other photos and images used with kind permission of National Savings and Investments (NS & I). With thanks to the Science Museum, NS & I, and BT Heritage.

If you have a query about money or bonds held in National Savings, please visit the National Savings and Investments site.

Design, images and text compiled by © Light-Straw. Page last updated Oct 2020. Checked May 2021.

All logos and trade marks are the property of their respective owners and are used on the Light Straw site(s) for review only. Students and researchers are recommended to make their own independent enquiries as to the accuracy of the information contained therein.