The Abundance Conjecture is a concept within the field of number theory, focusing on the behavior of certain algebraic integers. Specifically, it deals with the distribution of prime numbers and the density of subsets of integers with specific properties. While the conjecture has been discussed in various contexts, it is often associated with the idea that among the integers, there exists a rich abundance of those that exhibit certain arithmetic properties, such as being prime or having a specific number of divisors.
Fujitsu by Ciro Santilli 37 Updated 2025-07-16
The japanese name literally means:
  • 富士 fushi, from Mount Fuji, which itself has unknown origin
  • 通 tong: telecommunications
They died so completely, Googling "ICL" now has higher hits such as Imperial College London.
Video 1.
Why the UK's IBM Failed by Asianometry (2022)
Source. Main lesson perhaps: don't put national money to fight already established markets. You have to fight for what is coming up next. E.g. that is part of the reason for TSMC's success.
IBM by Ciro Santilli 37 Updated 2025-07-16
As of the 2020's, a slumbering giant.
But the pre-Internet impact of IBM was insane! Including notably:
IBM System/360 by Ciro Santilli 37 Updated 2025-07-16
This is a family of computers. It was a big success. It appears that this was a big unification project of previous architectures. And it also gave software portability guarantees with future systems, since writing software was starting to become as expensive as the hardware itself.
IBM 650 by Ciro Santilli 37 Updated 2025-07-16
This was the first major commercial computer hit. Stlil vacuum tube-based.
Video 1.
Learning how to program on the IBM 650 Donald Knuth interview by Web of Stories (2006)
Source. It was decimal!
IBM 1401 by Ciro Santilli 37 Updated 2025-07-16
Video 1.
The IBM 1401 compiles and runs Fortran II by CuriousMarc (2018)
Source.
Laser by Ciro Santilli 37 Updated 2025-07-16
What makes lasers so special: Lasers vs other light sources.
Video 1.
How Lasers Work by Scientized (2017)
Source.
An extremely good overview of how lasers work. Clearly explains the electron/photon exchange processes involved, notably spontaneous emission.
Talks about the importance of the metastable state to achieve population inversion.
Also briefly explains the imperfections that lead to the slightly imperfect non punctual spectrum seen in a real laser.
Video 2.
Laser Fundamentals I by Shaoul Ezekiel
. Source. 2008, MIT. Many more great videos in this series.

Pinned article: Introduction to the OurBigBook Project

Welcome to the OurBigBook Project! Our goal is to create the perfect publishing platform for STEM subjects, and get university-level students to write the best free STEM tutorials ever.
Everyone is welcome to create an account and play with the site: ourbigbook.com/go/register. We belive that students themselves can write amazing tutorials, but teachers are welcome too. You can write about anything you want, it doesn't have to be STEM or even educational. Silly test content is very welcome and you won't be penalized in any way. Just keep it legal!
We have two killer features:
  1. topics: topics group articles by different users with the same title, e.g. here is the topic for the "Fundamental Theorem of Calculus" ourbigbook.com/go/topic/fundamental-theorem-of-calculus
    Articles of different users are sorted by upvote within each article page. This feature is a bit like:
    • a Wikipedia where each user can have their own version of each article
    • a Q&A website like Stack Overflow, where multiple people can give their views on a given topic, and the best ones are sorted by upvote. Except you don't need to wait for someone to ask first, and any topic goes, no matter how narrow or broad
    This feature makes it possible for readers to find better explanations of any topic created by other writers. And it allows writers to create an explanation in a place that readers might actually find it.
    Figure 1.
    Screenshot of the "Derivative" topic page
    . View it live at: ourbigbook.com/go/topic/derivative
  2. local editing: you can store all your personal knowledge base content locally in a plaintext markup format that can be edited locally and published either:
    This way you can be sure that even if OurBigBook.com were to go down one day (which we have no plans to do as it is quite cheap to host!), your content will still be perfectly readable as a static site.
    Figure 2.
    You can publish local OurBigBook lightweight markup files to either https://OurBigBook.com or as a static website
    .
    Figure 3.
    Visual Studio Code extension installation
    .
    Figure 4.
    Visual Studio Code extension tree navigation
    .
    Figure 5.
    Web editor
    . You can also edit articles on the Web editor without installing anything locally.
    Video 3.
    Edit locally and publish demo
    . Source. This shows editing OurBigBook Markup and publishing it using the Visual Studio Code extension.
    Video 4.
    OurBigBook Visual Studio Code extension editing and navigation demo
    . Source.
  3. https://raw.githubusercontent.com/ourbigbook/ourbigbook-media/master/feature/x/hilbert-space-arrow.png
  4. Infinitely deep tables of contents:
    Figure 6.
    Dynamic article tree with infinitely deep table of contents
    .
    Descendant pages can also show up as toplevel e.g.: ourbigbook.com/cirosantilli/chordate-subclade
All our software is open source and hosted at: github.com/ourbigbook/ourbigbook
Further documentation can be found at: docs.ourbigbook.com
Feel free to reach our to us for any help or suggestions: docs.ourbigbook.com/#contact