2014-11-04 meeting round-up

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Tom Stuart

Nov 10, 2014, 6:07:53 AM11/10/14
to Computation Club mailing list

Before we all forget, and for those who couldn’t make it this time, here’s a brief summary of what happened at last week’s London Computation Club meeting:

As agreed previously, we made a start on reading “The Elements of Computing Systems”. By my count there were about 14 of us (https://www.flickr.com/photos/tomstuart/15096665303); after some initial introductions and discussion, we began looking through Chapter 1.

James Mead showed us a NAND gate he’d built from two transistors (https://www.flickr.com/photos/tomstuart/15096053374) and we went on to design NOT, AND, OR, XOR and MUX chips on the whiteboard. This stimulated enough interesting discussion that we didn’t have time to get onto the DMUX, multi-bit or multi-way chips.

A few points of discussion:

* How should we approach the book? Should we do the reading at the meetings and work on the projects as homework, or vice versa? The general consensus seemed to be that the latter would be more fun, so for now we’re expecting to read the book at home and then work on the projects (whether on whiteboards or on the computer) together when we meet.

* What is the “best” or “most efficient” way to design these chips? Paul Mucur demonstrated the canonical construction of each chip from its truth table, and we talked about various techniques (e.g. De Morgan’s laws, Karnaugh maps) for refactoring the Boolean expression representing a chip.

* What does it mean for a chip to be “most efficient”? Do we mean fewest NAND gates, or fewest (previously defined) parts, or fewest wire crossings, or what? We didn’t decide.

* Should we write our own hardware simulator in Ruby and/or JavaScript? There was general enthusiasm for this idea, but we didn’t even make it through the Chapter 1 exercises, so the point was slightly moot. James Coglan has since argued convincingly (https://groups.google.com/d/msg/london-computation-club/8mWclQpOu_Y/ptSazz4R_tAJ) that it wouldn’t be a good use of our time.

* What will the next meeting consist of, and what should we do as homework before then? We didn’t have time to agree this, and said we’d discuss on the mailing list. (This hasn’t happened yet, beyond Chris Lowis’s initial proposal at https://groups.google.com/d/msg/london-computation-club/NexNGnv3FIo/q1aOLqxLaRoJ.)

There’s more information (photos, links, our Ruby implementations of the logic gates) in my earlier email to the list: https://groups.google.com/d/msg/london-computation-club/xIwrj4I_oIw/O2D_tPweGWsJ


Paul Mucur

Nov 10, 2014, 6:40:36 AM11/10/14
to Tom Stuart, Computation Club mailing list
Thanks for this, Tom.

James Mead also suggested enabling the wiki on the web site GitHub
repo (which I just have:
https://github.com/computationclub/computationclub.github.io/wiki) so
that people could collaborate on the meeting notes. We could then link
to these from the main site?

My vote is to push on to Chapter 2 (working through Chapter 1 and its
exercises if you haven't already done so) and go through the exercises
together in the next meeting.

I agree with James Coglan that we should avoid getting too sidetracked
so early on with re-implementing the simulator particularly as Roland
warned that there is a steep change in difficulty coming up. If we do
manage to start breezing through things then we can re-evaluate but it
felt like we had more than enough to talk about just with the most
basic of exercises.
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Paul Mucur

Nov 10, 2014, 6:44:52 AM11/10/14
to Tom Stuart, Computation Club mailing list
Also worth noting that we encourage everyone to add themselves to the
"Members" section of the site by raising a pull request against

(We did mention inviting people to do this on the site itself so bonus
points if your PR includes something to that effect.)

Jamie White

Nov 10, 2014, 7:42:02 AM11/10/14
to Paul Mucur, Tom Stuart, Computation Club mailing list
Chapter two is relatively short and could be comfortably read over a lunch break (if you’ve left it to the last minute). The exercise is a nice step up from Chapter 1’s. Should make for a fun group exercise :D

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