[Simon Tatham, 2025-03-12]

• Introduction
• Hand-drawn era
  • PuTTY itself
  • PSCP (and PSFTP): file transfer
  • Pageant: SSH agent
  • PuTTYgen: key generator
  • Configuration dialog box
• Scripted era
  • pterm
  • Installer
• SVG revamp
• That’s all, folks!

Introduction

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.

Sometimes I receive an email asking a question, and by the time
I’ve finished answering it, I realise it’s worth turning into a
blog post. This time I knew it was going to be one of those
before I even started typing, because there’s a graphic design
angle to the question and a technical angle. So I had a
lot to say.

PuTTY’s icon designs date from the late 1990s and early 2000s.
They’ve never had a major stylistic redesign, but over
the years, the icons have had to be re-rendered under various
constraints, which made for a technical challenge as well.

Hand-drawn era

When I first started drawing PuTTY icons, I didn’t know I was
going to need lots of them at different sizes. So I didn’t start
off with any automation – I just drew each one by hand in the
MSVC icon editor.

PuTTY itself

Expanded to a visible size, here’s the earliest version of the
original PuTTY icon that I still have still in my source
control. That means it was current in early 1999; my source
control doesn’t go all the way back to the very project start in
the summer of 1996, but if it did, I expect this
was probably the same icon I originally drew. I’d have
drawn one quite early, because Windows GUI programs look pretty
unhelpful without an icon.

It’s 32 × 32 pixels, and uses a limited palette of primary
colours and shades of grey. That’s because I started the project
in the mid-1990s, when non-truecolour displays were very common.
There was a fixed 16-colour palette recommended for use in
icons, consisting of the obvious primary and secondary colours
and dim versions of them, plus a couple of spare shades of grey.
That way all the icons in the entire GUI could reuse the same 16
palette entries and not run the display out of colours. So this
icon is drawn using that palette.

Providing a plain black-and-white version was another standard
recommendation at the time. But I can’t remember why – I
certainly never actually saw a computer running Win95
or later with a B&W display! My best guess is that the
recommendation was intended for use with the “Win32s” extension
that would let 32-bit programs at least try to run on
Windows 3.1 (on suitable underlying hardware). Probably Windows
3 still supported black and white displays.

I don’t think I thought about the design very much. I just
dashed it off because I needed some kind of an icon.
The two computers are drawn in a style that was common in the
’90s: a system box sitting under a CRT monitor, with a floppy
disk drive visible at the right-hand end. They’re connected with
a lightning bolt to suggest electrical communication between
them. I didn’t believe I was being very original: I had
the vague idea that several icons of this kind already existed
(although I’ve never been able to find any specific example of
what I was thinking of), so in my head, it fit with the general
iconography of the day, and seemed as if it would be immediately
understandable.

I can’t remember why the lightning bolt was yellow.
With hindsight that seems the strangest thing about it; cyan
would have been a more obvious choice for electricity. Possibly
it was just to contrast more with the blue screens of the
computers.

Speaking of which … I can’t remember why the screens were blue,
either. I think I just intended it as a neutral-ish
sort of colour which wasn’t black, so that it was clear that the
screens were turned on. I’m pretty sure the blue wasn’t
an allusion to the Windows Blue Screen of Death – that wouldn’t
make sense, because in a typical use of PuTTY, only one
end of the connection is running Windows, and neither end has
crashed!

Looking back, I suppose I might also have considered making the
two computers look different from each other, on the theory that
the client machine might be sitting on someone’s desk, and the
server might be in a rack in a datacentre? But I was a student
when I started writing PuTTY, and my Linux server you
could remotely log into was on my desk and not in a rack. So I
think that just never even occurred to me.

PSCP (and PSFTP): file transfer

In 1999, a contributor sent an SCP implementation, and PSCP was
born. I decided to draw it an icon of its own.

It wasn’t especially important for PSCP to have an icon at all.
You don’t run it from a GUI (it’s useless without
command-line arguments), so it doesn’t need an icon for you to
find it in Explorer or identify it in the Start Menu. And it
doesn’t put up GUI windows, so it wouldn’t need an icon to
identify those in the taskbar either. But I drew an icon anyway.
I can’t remember why. Maybe it was just for completeness, or I
felt like doing a bit of drawing, or something.

I made the PSCP icon by modifying the existing PuTTY icon,
replacing one of the two computers with a piece of paper with
variable-length lines on it, suggesting a written document:

I kept the lightning bolt connecting the remaining computer to
that document, the theory being that you use PSCP to remotely
access documents. (In some fairly vague sense.)

Later on, we gained a second file transfer tool, PSFTP, and I
reused the same icon for that, on the basis that they’re both
file transfer tools and the icon doesn’t really say anything
specific to one of them. PSFTP is still a command-line
application, but unlike PSCP, it’s possible to run
it from the GUI (by clicking on it in Explorer or the
Start Menu), because it has an interactive prompt, so if you
don’t run it with any command-line arguments, you can tell it at
the prompt where to connect to. So PSFTP put the same icon to a
more practical use than PSCP did.

(On the other hand, giving two tools the same icon means you
have to check carefully which one you’re dragging around in
Explorer! Perhaps it would have been better to make the PSCP and
PSFTP icons different in some way. But I couldn’t easily think
of a visual depiction of the ways the two tools differ.)

Pageant: SSH agent

Pageant, our SSH agent, was the next tool in the suite that
needed an icon.

My original idea for an icon depicting an SSH agent was to draw
the face of a secret agent – in the stereotypical
outfit from the sillier end of spy fiction, with a wide-brimmed
hat and a turned-up collar.

But I’m terrible at drawing faces. After a few failed attempts,
I realised that Pageant would never get released at all
if I