Simon Tatham

chiark.greenend.org.uk/~sgtatham

Welcome to my web site. I'm Simon Tatham, a software engineer and free-software author in Cambridge, UK.

Popular posts: 16
Total points: 4,224
HN comments: 1,891
Rank: #296 personal

Visit chiark.greenend.org.uk/~sgtatham → On Hacker News May 2010 – May 2026

Software Engineering 10 Open Source 5 Security & Privacy 4 Math & Algorithms 4 Systems & Performance 2 Tools & Productivity 1

Most points Most discussed Most cited Newest

XOR

2025602 points100 comments Math & Algorithms details

Recently I was called on to explain the ‘XOR’ operator to somebody who vaguely knew of its existence, but didn’t have a good intuition for what it was useful for and how it behaved.

PuTTY vulnerability vuln-p521-bias

2024558 points212 comments Security & Privacy details

Iconography of the PuTTY tools

2025400 points105 comments Design & UX details

In March 2025 I received an email asking about PuTTY’s “logo” – the icon used by the Windows executable. The sender wanted to know where it had come from, and how it had evolved over time.

The descent to C

2014377 points321 comments Software Engineering details

This article attempts to give a sort of ‘orientation tour’ for people whose previous programming background is in high (ish) level languages such as Java or Python, and who now find that they need or want to learn C.

Git without a forge

2025322 points159 comments Software Engineering details

I’ve written quite a lot of free software in my life. Most of it was from scratch: projects I started myself. So I get to choose where to host them – or rather, I have to choose where to host them.

Coroutines in C (2000)

2024307 points168 commentscited by 54Software Engineering details

Structuring a large program is always a difficult job. One of the particular problems that often comes up is this: if you have a piece of code producing data, and another piece of code consuming it, which should be the caller and which should be the callee?

Nitpicking the shell history scene in 'Tron: Legacy'

2026305 points125 comments History & Retro Computing details

In the 2010 film Tron: Legacy , there's a scene where the main character Sam Flynn sits down at a computer in his father’s study, and types some commands to try to figure out what Flynn senior had last been working on, before mysteriously disappearing.

PuTTY 0.68 has been released

2017243 points147 comments Security & Privacy details

Possibly all the ways to get loop-finding in graphs wrong

2024230 points51 comments Math & Algorithms details

In my puzzle collection , there are many games in which you have to connect points together by edges, making a graph, and the puzzle rules say you must avoid making any loop in the graph. Examples are Net , Slant , and some configurations of Bridges (although not the default one). Loopy and Pearl also care about…

Two algorithms for randomly generating aperiodic tilings

2023195 points42 comments Math & Algorithms details

[Part of a series: Penrose and hats | Spectres | finite-state transducers | more transducers | refining tilings ]

Philosophy of Coroutines

2023171 points78 comments Software Engineering details

I encountered the idea as a student, when I first read The Art of Computer Programming . I’d been programming already for most of my childhood, and I was completely blown away by the idea, which was entirely new to me. In fact, it’s probably not an exaggeration to say that in the whole of TAOCP that was the single…

PuTTY 0.63 released, fixing four security holes

2013138 points156 commentscited by 29Security & Privacy details

Code review antipatterns

2024131 points122 comments Software Engineering details

Code review seems like a great idea, right? Two developers looking at the same code means two chances to spot problems; it spreads understanding of the way the project is evolving; the reviewer can learn useful tricks from reading the author’s code in detail, or spot opportunities to teach the author a useful trick…

A pair of dice which never roll 7 (2004)

2022130 points53 comments Math & Algorithms details

Some friends of mine play the board game Settlers Of Catan . In this game, each player rolls two ordinary dice on their turn, and the number which comes up determines what resources people get for the turn. When a seven is rolled, something special happens: no resources are generated, and instead a robber moves on the…

PuTTY 0.66 fixes security vulnerability

2015115 points52 comments Security & Privacy details

How to Report Bugs Effectively

2010cited by 11Software Engineering details