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diff --git a/zk/Delay_line_memory.md b/zk/Delay_line_memory.md
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+++ b/zk/Delay_line_memory.md
@@ -0,0 +1,22 @@
+---
+title: Delay_line_memory
+tags: [computer-history, memory]
+created: Wednesday, September 18, 2024
+---
+
+# Delay line memory
+
+- First described in the _First Draft_ by #vonNeumann based on work by Eckert
+  and Mauchley.
+
+- Information is stored as acoustic waves travelling through a medium, typically
+  mercury. As sound travels more slowly than electric charge (light), if
+  electric signals are converted to sound, the delay time involved can be used
+  as a type of store.
+
+- It worked as follows:
+  - Imagine we have an 8-bit number. The number is input as a sequence of pulses
+    where a pulse is 1 and the absence of a pulse is 0.
+  - The pulses are converted into sound waves (as with a speaker) and sent
+    through a mercury-filled tube.
+  - The length of the tube
diff --git a/zk/The_History_of_Computing_Swade.md b/zk/The_History_of_Computing_Swade.md
index 12be604..4de14a2 100644
--- a/zk/The_History_of_Computing_Swade.md
+++ b/zk/The_History_of_Computing_Swade.md
@@ -334,20 +334,26 @@ the ABC to make ENIAC.
 ### Concept of the _internal stored program_
 
 - Key innovation of the EDVAC was the _internal stored program_ (ISP).
+
 - Solution to the problem of preceding computers requiring down-time when
   switching between applications and problem sets.
+
 - Circuitry would need to be reconfigured before the computer could run on the
   next problem
+
 - ISP removed the friction:
+
   - the instructions comprising the program would be prepared on tape or punched
     cards and read into electronic memory
   - the hardware configuration of the machine would remain the same accross
     different programs and require no reconfiguration, only the input program
     data would change
+
 - This was basically the invention of software. Both instructions and data
   shared the same memory space once they were read-in. Before, the data would be
   stored in memory but the instructions would be read one-by-one from the
   external storage media.
+
 - Key consequences:
   - flexibility (no need for re-wiring)
   - speed: fetching instructions from memory is quicker than fetching from
@@ -364,26 +370,46 @@ the ABC to make ENIAC.
 ### Post-EDVAC devices
 
 There were several notable devices which attempted to implement the architecture
-described in the _First Draft_ using vacuum tubes:
+described in the _First Draft_ using vacuum tubes and other fully-electronic
+methods for memory:
 
 - the Manchester "Baby"
 - the Cambridge EDSAC
 - Turing's ACE computer
 
-#### Manchester Baby
+#### Manchester Baby (1948)
 
 - An experimental computer intended to create the
   [von Neumann architecture](CPU_architecture.md) using
   [Williams_Tube_RAM](Williams_Tube_RAM.md)
+
 - Developed at the Univesity of Manchester and completed in 1948.
+
 - Considered the first electronic stored-program computer and first to contain
   all the elements of a modern electronic digital computer.
 
-#### EDSAC
+#### EDSAC (1949) J.Wilkes et al.
 
 - _Electronic Delay Storge Automatic Computer_
+
 - Constructed by Maurice Wilkes and others at the Mathematical Laboratory
-  Cambridge University (UK).
+  Cambridge University.
+
 - The second digital stored-program computer after the Manchester Baby.
+
 - It used vacuum-tubes for the arithmetical operations in the ALU and mercury
   delay lines for the RAM.
+
+- Designed to be used by relatively non-specialist practitioners from other
+  university departments who were expected to program it themselves. To this
+  end, a formal programming paradigm was forged for the EDSAC which established
+  the following:
+
+  - subroutines as a library of common procedures available to programmers (e.g.
+    printing a result, reading input tape, program checking, mathematical
+    operations)
+  - diagnostics: techniques for verifying program code and its correctness
+
+- The key players wrote the first textbook on programming in 1951: _The
+  Preparation of Programs for an Electronic Digital Computer_ (Wilkes, Wheeler,
+  and Gill)
diff --git a/zk/Williams_Tube_RAM.md b/zk/Williams_Tube_RAM.md
index 6fa23a0..7aa38f9 100644
--- a/zk/Williams_Tube_RAM.md
+++ b/zk/Williams_Tube_RAM.md
@@ -8,13 +8,16 @@ created: Tuesday, September 17, 2024
 
 - One of the early attempts to create RAM in computers based on the EDVAC
   stored-program architecture.
+
 - Worked by displaying a grid of dots on a cathode-ray tube ("screen")
+
 - Due to the way CRTs work, this creates a small charge of static electricity
   over each dot. The charge at the location of each of the dots is read by a
   thin metal sheet just in front of the display.
+
 - Each dot position could be written to and read from and the pattern was
   constantly refreshed as the dots would fade over time.
 
-[A Williams CRT tube](../img/williams-tube.jpg)
+![A Williams CRT tube](../img/williams-tube.jpg)
 
-[Memory dot pattern from a Williams Tube](../img/williams-tube-dots.jpg)
+![Memory dot pattern from a Williams Tube](../img/williams-tube-dots.jpg)