How Computers Calculate - the ALU: Crash Course Computer Science #5

preview_player
Показать описание
Today we're going to talk about a fundamental part of all modern computers. The thing that basically everything else uses - the Arithmetic and Logic Unit (or the ALU). The ALU may not have to most exciting name, but it is the mathematical brain of a computer and is responsible for all the calculations your computer does! And it's actually not that complicated. So today we're going to use the binary and logic gates we learned in previous episodes to build one from scratch, and then we'll use our newly minted ALU when we construct the heart of a computer, the CPU, in episode 7.

*CORRECTION*

We got our wires crossed with the Intel 4004, which we discuss later. The 74181 was introduced by Texas Instruments in 1970 but appeared in technical manuals around 1969. The design of the 74181, like most of the 74xx/74xxx series, was an open design which was manufactured by many other companies - Fairchild was one such manufacturer. They produced a chip, the Fairchild 9341, which was pin-for-pin compatible with the 74181.

Fairchild was the first to prototype an ALU, building the Fairchild 4711 in 1968 - a one-off device not optimized for scale manufacturing. In 1969, Signetics came out with the 8260, which they marketed in a very limited sense (it was attached, AFAICT, to one particular computer, the Data General SUPERNOVA). TI follows afterwards (March 1970) with the 74181, coupled with the 9341 from Fairchild. The 74181 became the standard number for this part, and was available from many manufacturers (back in those days, chip makers cross-licensed designs all over the place in order to provide assurance that their part could be sourced from multiple manufacturers).

We’ve got merch!

Want to know more about Carrie Anne?

Want to find Crash Course elsewhere on the internet?

Want to find Crash Course elsewhere on the internet?

Рекомендации по теме
Комментарии
Автор

I'm a computer engineering student and I'm truly impressed by how good these videos are! Congratulations!

ricardolages
Автор

I'm a computer engineer, and I have to say that I am really impressed by the quality of this series. Nice way to summarize a 4-year degree program! And that "new level of abstraction" thing is all that computer engineering really is. You might as well call it abstraction engineering :p

UdeyRishi
Автор

I love how you explain the levels of abstraction. Each time something seems overcomplicated, I just remember that it's just a bunch of transistors wired up in clever ways at the core of it all and at the core of those transistors are on and off electric signals. Helps me relax and admire the beauty and craftsmanship of computers.

domobrah
Автор

I took a computer architecture course at university and we build an 8-bit ALU that could Add, Subtract, AND, OR, XOR, and a few other logic functions that I can't remember for sure (maybe multiply and divide). We designed a PCB and sent off our design to be manufactured. Then we soldered the chips into our board ourselves. It was a really fun project.

vkillion
Автор

i'm a 34 year old software developer that's become burnt out.

This series is reminding me that this stuff is fun and exciting and not just "oh my god why is this library broken?"

taitaisanchez
Автор

In binary when you add 1+1, you get 0 and Carrie Anne.

migueldoliveiracomposer
Автор

As a side note to those wondering how subtraction is done, it is also done through addition. The way computers store negative integers in binary is a system called 2's complement, which is difficult to discuss in a short text comment, but it allows the addition of a positive integer X and a negative integer Y to equal X - Y. If you want to subtract Y from X you just turn Y into a negative number (which is a very fast operation) and then add them together.

MFMegaZeroX
Автор

I've just started watching this, Crash Course mythology, sociology and physics. Much to my surprise, I've enjoyed this one the most!

basiec.
Автор

Me: It's simple as 1+1!
ALU: Is it really?

clock
Автор

being a professor of computer science I have to say that I really think you are doing a great job! keep it up!!!

HemmligtNavn
Автор

It's somewhat worrisome just how happy this series makes me. Carrie Anne does a great job explaining the basics (and the abstractions that follow), the writers have put in just the right amount of detail and the animators are, as always, exemplary.

I spent a decade writing low level code for microcontrollers, bit slice processors and very early GPUs. I lived at the ALU level, passing data from register to register while checking flags. These days I program for the web and it's so much more abstract than physically pushing bits from A to B; I kind of miss the simplicity ;-)

RedwoodGeorge
Автор

*inhales deeply* good lord I am going to need all of my brain power to understand this.

eugenio
Автор

I can't believe crash course is now doing a computer science course. I'm kind of really proud that they've come so far

SuperHappyNotMerry
Автор

The more I watch CrashCourse, the more I want to complain as to why this kind of video wasn't around when I was in high school. Could have helped me a lot when I need to look up something that I have forgotten, but I can't understand what my textbook was trying to say to me to get me to understand to concept.

NJCProductions
Автор

I don't have a background in computer science at all whatsoever, so these concepts are completely new to me. This series is doing a great job at explaining the concepts, and I feel like I kind of understand it even though I haven't heard of any of these things before. And the host is great, too. Keep it up!

KerriCz
Автор

I'm studying computer engineering (Sophmore) and this series turned out to be more valuable than my entire first semester! Thanks to everyone who is involved with the production. Cheers!! I'm gonna watch every playlist on this channel during the Quarantine now.

taleofkaran
Автор

This is such a great series, definitely one of the best crash courses. you guys are nailing it

mostlyfocused
Автор

CrashCourse is amazing. I didn't think I'd ever get the privilege of understanding how a computer works or how a muscle works on the cellular level. Keep up the excellent work!

abramwicasatheca
Автор

It's like I'm looking at my computers soul.

johnarken
Автор

For the longest time I've believed that electrical engineering coursework is not hard instrinsically, but made unnecessarily difficult with confusing and boring lectures from professors who've been given no incentive to rethink how to best teach the content. This video series is complete validation of that. The clarity with which CrashCourse/PBS Digital presented this is awe-inspiring. Thank you so much!

ZubairKhan-ttev