Ceefax

Ceefax was the BBC's teletext service. It began transmission on BBC2 in 1973 and ceased to be available publicly in 2012, following the completion of the UK's Digital Switchover.

Early History

The earliest discussion of a teletext-like system happened as far back as 1970. A note from P. Rainger, then head of the BBC's design department, mentions the possibility of generating characters independently of a normal television programme.

Early experiments in 1971 used a subcarrier in the TV system's sound channel to carry information, much like RDS today - however the bitrate was limited to only around 15kb/s before it negatively affected the programme audio.

Further experiments in the later half of the year focused on using the VBI portion of the television signal - however using a bitrate of 2.5MHz, only 15 characters could be transmitted per line, which was felt to be inadequate. The advent of Non-Return-To-Zero Coding allowed the bitrate to be almost doubled to 4.5MHz - this allowed 32 characters to be transmitted per line. Lines 13, 14, 326 and 327 were chosen for the system, as these lines did not cause bits to appear on the picture during the CRT retrace.

The BBC announced the new Ceefax service on the 23rd of October 1972.

Until 1973 Ceefax and IBA's ORACLE service used their own incompatible standards; for example, a Ceefax page consisted of 24 rows each containing 32 characters, whilst ORACLE's consisted of 22 rows with 40 characters. After representatives from the BBC, IBA, Post Office and manufacturers met monthly in the later half of 1973, agreement was reached and a standard published in March 1974. This defined the 24 row, 40 character pages with which we are familiar today.

More History

Probably be better to let someone historically minded to do this bit

Later history and demise

Ceefax began to disappear from homes across the UK as early as 2005, when the first trials for the nationwide Digital Switchover began. While it could have been continued over digital television, the BBC instead decided to replace it with the new BBCi, later BBC Red Button, MHEG5 service. Ceefax officially ended on the 24th of October 2012 when the final stage of digital switchover completed in Northern Ireland. However, it continued to be available inside BBC Television Centre up to a year later, albeit not updated.