Binary Coded Decimal (BCD) & Douglas Adams' 42 - Computerphile

Just how do you go from a binary number to a printed out numeric character? Professor Brailsford takes us through Binary Coded Decimal

This video was filmed and edited by Sean Riley.

[TheTwick]

Professor Brailsford, NEVER STOP telling us stories about computers and computing. I could listen all day.

[profdaveb]

Yes, I just wanted to show that "Computerphile" presenters other than Dr Bagley are also allowed to wear Hawaiian shirts! This particular one was bought about 8 years ago at Macy's, in Stanford University's Shopping Mall.

[ZXK]

The ASCII equivalent of 42 is asterisk. The asterisk is used in computing to represent 'anything'. So the answer to life, the universe and everything is anything ;)

[vylbird]

The exact wording is important. The Deep Thought was specifically asked "What is the answer to the ultimate question of life, the universe and everything?"

The answer it eventually gave was 42. It was not, however, able to compute the ultimate question itsself, to which 42 was the answer.

[bbjedump]

Why weren't my teachers more like this guy?! Hats off to the knowledge and experience.

[ezwa]

42 in binary is (mentioned in the video) 101010. When Parliament of the Czech Republic (where I am from) agreed a law on digital broadcasting or digital phoning or whatever digital (I can't remember), they made it valid since 10. October 2010, or 10.10.10. They I believe proved their sense of humor...

[Zadster]

Top choice of shirt Prof. B!
Every time I see one of these videos, I get nostalgic for when I was an undergrad, and a wee bit jealous of all those people about to go to university to learn all sorts of amazing new things. Good times!

[Xilefian]

I was programming some stuff with binary coded decimal the other day. It's still used for real-time clock chips! If you want the bare-metal low level time from these chips they give you BCD, presumably because it's easier to print BCD out to cheap digital displays than to convert an integer to a string.
EDIT: Yep you mentioned digital clocks at the end of the video! Very excellent.

[nikolaradakovic]

You Sir Dave bring internet to a very different level of usefulness . Thank you for such a high quality yet free content.

[RMoribayashi]

HP scientific calculators all used BCD so avoided the rounding problems inherent in a true binary calculator. In 2004 Thomas Okken's released his exellent HP-42 simulator, Free42. It comes in both BCD and the slightly faster floating point binary versions. SwissMicros brought it full circle in 2017 when they released the DM-42, a physical calculator based on the HP-42 but using a modified version of Free42 for it's firmware. And yes... it uses BCD.

[grantnichol]

The double dabble algorithm is a pretty great way to convert beateeen binary and BDF. It's how you can output to an lcd screen at the end of an arythmatic unit.

[cyndicorinne]

What a beautiful explanation and historical context of BCD.

[sudoLife]

Every video of yours is like a journey through the time and brains of engineers & scientists!

[tonycolle]

I love these journeys into history. It's actually very important to have some knowledge of these topics so people who want to be Computer Scientists and not just programmers (although there is nothing wrong with the profession) know how we got to where we are and where we might be heading in the future. Is there some chance that Professor Brailsford or someone can do a session on packed decimal? That is the technology on which so much of the financial world was built and still lives today.

[amprocha]

Thank you sir.
I always appreciate your brilliant way to express your vast knowledge.

[tabaks]

An episode on FUNDAMENTAL differences between AI and classical programming would be GRAND! Basically, for the lay person, why AI isn't just a giga-complex classical programming effort that is pre-loaded with all possible outcomes...

[philrod]

8-bit arcade machines use BCD for displaying scores, etc. on the screen. The Z80 CPU has the DAA instruction for _fixing_ BCD values after ADD, SUB, etc.

[typograf]

DAA - decimal adjust accumulator. An instruction on the Z80. Fixes decimals overflowing into hexadecimal.

[agstechnicalsupport]

Great video on the importance and use of Binary Coded Decimal (BCD). Thank you !

[Slithy]

"Heavyweight macho calculations". I love it.