(docs) readme - Change intro + change meaning of "ECG"

readme.md

@@ -1,9 +1,25 @@
 # Cardiograph computers
 
-The Cardiographs are a pair of imaginary computers:
+The Cardiographs are a pair of imaginary computers,
+designed as educational toys.
 
-- "Cardiograph Mark I" is an educational model of a mainframe machine
-- "MicroCardiograph" is a its miniaturized descendent, a microprocessor trainer
+Inspired by the CARDIAC paper computer,
+they are intended to be simple enough to build as
+hand-operated paper models.
+
+Their design is guided by two additional criteria:
+
+1. They should be capable of producing interesting graphical output
+2. They should accurately model the functioning of a real computer
+   (by operating on binary data, for example)
+
+## The two computers
+
+The two Cardiograph computers are:
+
+1. the _Cardiograph Mark I_ (CG) is a mainframe machine
+2. the _Micro Cardiograph_ (µCG) is a microprocessor trainer
+   (a miniaturized descendent of the mainframe)
 
 They use the same instruction set and have very similar CPUs. (TODO: is that true?)
 
@@ -11,11 +27,9 @@ The main difference is in their peripheral hardware:
 the Mark I is designed for batch processing and supports punched-card input,
 while the MicroCardiograph is designed to be used interactively.
 
-The Cardiographs were built by an imaginary enterprise, the Electronic Computer Group (ECG).
-
 ## Simulator
 
-There is a [simulator](micro/readme-micro.md) for the MicroCardiograph.
+_[Micro ElectroCardiograph (µECG)](micro/readme-micro.md)_ is a simulator for the Micro Cardiograph.
 
 ## CPU
 
@@ -127,10 +141,10 @@ Put differently: it starts executing instructions at the address contained in `$
 
 The components of a Mark I are:
 
-- an ECG 101 Central Processing Unit
-- an ECG 102 Core Memory Unit
-- an ECG 103 Print-Key-Punch
-- an ECG 104 Matrix Display
+- an CG 101 Central Processing Unit
+- an CG 102 Core Memory Unit
+- an CG 103 Print-Key-Punch
+- an CG 104 Matrix Display
 
 ### Console