Brief commercial announcement yeah sure I think I mentioned at some point in our

conversation the fact that the people working on MULTICS, well MULTICS was sort of the

second version of timesharing that was done at MIT with collaboration of Bell

Labs and General Electric very big

system for providing in effect a computing utility for programmers.

Multex was actually being written in high-level languages ah they started with PL1

which was not a good choice and then they moved to BCPL

language which developed in fact by Martin Richards of Cambridge.

The people doing that who are at Bell Labs in particular Ken Thompson and Dennis

Ritchie had gotten used to the idea that you could write really interesting

operating system kind of software and tools that supported it in high-level

languages so you weren't writing assembly language and so when they

started working on UNIX this very small stripped-down version that was done at

Bell Labs they were at the same time exploring the use of high-level

languages and there were a variety of these there was a language called B

which was the first attempt it was done by Ken Thompson a very simple language

and I suppose you could say it was sort of like a stripped down version of BCPL

A weak naming convention there and so you could do interesting things with

B but it wasn't quite powerful enough and in particular it was an interpreter

not a compiler and that meant it didn't generate machine code for the particular

machine was running on it was just a program that

interpreted what it was trying to say so it meant it ran relatively slowly.

The other thing is that the language did not support the architecture of newer

machines that were showing up in particular that PDP 11 newer machines

instead of having everything in the machine be a single size of in effect integer

let's say 16 bits or something like that they had different sizes that were, the

machine would efficiently and naturally manipulate 8bit, 16bit maybe thirty

two-bit & the language B didn't reflect that and so Dennis Ritchie undertook

to design what amounted to a version of B that was richer and had mechanisms

in the language to say this is an 8-bit quantity this is a 16 bit quantity

basically the char and int types that you see in the early versions of C and so he

wrote

a compiler for that and then with the compiler in hand they started to rewrite

the operating system itself in C and this took a while but something in the

order of six months to get that working and at that point then you've got the

operating system of course all kinds of other critical core software written in

a high-level language rather than in assembly language and that's important

for all kinds of reasons one is means that it's just a lot easier for lots of

people to see what the code does you need so much expertise because it's a

high-level language and the other thing is that it's portable in the sense that

if somebody makes a C compiler for a different kind of machine different

architecture then you can recompile whatever your program is for that new

architecture in

that way you can move your program to a different machine of this always been

the advantage of high-level languages but now you could do it for the operating

system and that meant that UNIX, the operating system no longer was only PDP

11 but could run on a variety of other machines as well

I think the concept of having a high-level language Iget right, you compile it down to hexes, machine code that tells the processors to do stuff. and if you have a different compiler for a different machine

it just changes what those Hexes are -right that's exactly right

so so it should be really simple to understand how you write an OS in a high level language, but is it a bit like, making a sharp tool and using that sharp tool to make a sharper tool?

Yeah, right, I think in fact, the complication is in building in writing of operating system and high-level

language in translating it into let's say multiple different architectures is

there's a lot of detail to get right there in there are some things which the

high-level language just doesn't support So you need a little tiny bit of assembly

language assist for any given operating system the one that's more like that the

conceptual problem that you were explaining well is how does the compiler

itself get started because of course the C compiler is written in C so there is the

how do you get it started and your idea of the sharper tool making yet a sharper

tool and so on

is metaphorically the right idea because what you do is you say I wrote some code

in C on paper let me mechanically translate that into something that will

process a bit more of C code and bootstrap myself up from that so it's a

bootstrapping process and I've never done it so take me with a grain of salt

on that but that's the basic idea so. - OK, so tell me about this book, how did this come about?

that's the first edition (is it autographed?) this one isn't actually no dear oh dear this however is

the 24th printing so. (I'll just point out that Prof Brailsford brought in a pen for the autograph there.) OK I will autograph it...

somewhere early on in this process of people building interesting languages I

got intrigued by the idea of how do you explain those languages to other people

and so I wrote tutorial documents I wrote a tutorial document on B so that

people could learn B because Ken Thompson and to a lesser degree Dennis didn't

write tremendous amount of documentation let's say it was a spare and there was

not much tutorial stuff so I wrote a tutorial document on B that was useful

when C came along then I wrote a tutorial document on C and at some point

I had already written I guess couple books at that point and it seemed like

the market, the market!? That there might be a market for a C book and so I

twisted Dennis Ritchies arm into writing the book with me and that is the

smartest thing I ever did in my whole life no ambiguity so we took my tutorial

document as kind of a piece of it, we took his reference manual which is a

excellent reference manual as a big piece of it took that verbatim and then

we filled in material in the middle to explain the various parts of the language at length, and we

published that, we wrote it in 1977 published at the beginning of 78 and of

course it was done with all of the document preparation tools that we had

been working on over the years and so it had

mathematical expressions in it using EQN it had tables of things like

operators using Mike Lesk's TBL program it

the first edition predates pic the picture drawing language the second

edition has pic pictures so on so is this incestuous or is this building on

what people have done I don't know but that's how it came about and I remember

talking to the editor this is published by Prentice Hall with Karl Karlstrom the

editor there and I remember discussion with him about how many copies do you

think this will sell no idea well maybe five thousand

done better than that which is just as well

there never an A because B was based on? There was a language Steve Johnson who was all part of this the

creator of Yacc, Steve Johnson spent a sabbatical at University of Waterloo in Ontario and

he came back with a link I don't somebody else had done that the language

they're called "A" but it was spelled "EH" - Bit of Canadian humor I guess...