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diff --git a/zk/The_History_of_Computing_Swade.md b/zk/The_History_of_Computing_Swade.md
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--- a/zk/The_History_of_Computing_Swade.md
+++ b/zk/The_History_of_Computing_Swade.md
@@ -1,6 +1,7 @@
 ---
 title: Very_Short_History_of_Computing_2022
-tags: [literature, computer-history]
+tags:
+  [literature, computer-history, Leibniz, Babbage, Lovelace, Turing, Neumann]
 created: Friday, August 23, 2024
 ---
 
@@ -20,7 +21,7 @@ A typical timeline approach rooted in major innovations.
   Pascal, Leibniz)
 - Modern aids to calculation: slide rules following the discovery of
   [logarithms](Logarithms.md)
-- Mechanized calculating engines of Babbage in the 19th century
+- Mechanised, automated calculating engines of Babbage in the 19th century
 - Punched-card machines leading to IBM in the early 20th century
 - Analogue and electro-mechanical computers of the early 20th century inclusive
   of wartime computers
@@ -33,3 +34,64 @@ A typical timeline approach rooted in major innovations.
 - Consumer personal computers
 - Internet and later, Web
 - Smart phones
+
+## Mechanical calculating devices in the 17th century
+
+Focus was chiefly on creating a desktop calculator capable of four-function
+arithmetic.
+
+![Photograph of Pascaline](../img/pascaline.jpg)
+
+![Photograph of replica of Leibniz stepped drum machine](../img/leibniz-stepped-drum.jpg)
+
+The main contenders were Pascal's Pascaline (which only did cumulative addition)
+and Leibniz's wheel or "stepped drum" calculator that could do all operations
+(in theory).
+
+Subsequent designs were based on these artefacts. In practice, neither worked
+consistently well with the carriage of tens remaining a sticking point.
+
+![Photograph of Arithmometer](../img/arithmometer.jpg)
+
+![Photograph of Comptometer](../img/comptometer.png)
+
+The arithmometer (crank driven) and comptometer (key-driven) were descendents of
+the Leibniz design that became commercially viable by the 19th century along
+with other mechanical calculators. In the US, Burroughs dominated the market.
+
+## Babbage: mechanized, automated calculation
+
+> I wish to God these calculations had been executed by Steam (Babbage)
+
+With Babbage's machines we see an approach to computation that can only be
+understood against the backdrop of the Industrial Revolution in which they were
+conceived.
+
+The idea is that the machine is a factory and number is the product. In the same
+way as the mechanised looms created textiles. It is the extension of a model of
+industrial production from goods/commodities to information.
+
+Babbage conceived two machines: the Difference Engine (DE) and the Analytical
+Engine (AE). Neither were successfully built in his lifetime. The DE preceded
+the AE and was basically an advanced mechanical calculator whereas the AE
+approximated a general purpose computer.
+
+## Difference Engine
+
+The DE's single purpose was to calculate and output mathematical tables such as
+the results of polynomial equations. The idea was that you would input the
+variables of the equation and activate the machine and it would output the
+results. Associated with this concept was the idea that once it arrived at the
+answer a bell would ring and the machine would _halt_. This influenced Turing
+later. It was non-programmable and designed for a specific set of calculations.
+
+## Analytical Engine
+
+Conceived as a general-purpose computing machine capable of perfoming a wide
+range of calculations, programmable using punched cards similar to those used
+with Jacquard looms.
+
+It more resembled modern computers in that Babbage used concepts that would
+later translate into the von Neumann architecture. There was a "mill" (CPU),
+"store" (memory) and input/output mechanisms. It also had a concept of looping
+and conditional branching.