EDSAC Rebuild Project - Logic Reconstruction - CmpCol

Accumulator Shifting Unit 1
Accumulator Shifting Unit 2
Main Adder
Computer Control I
Computer Control X
Computer Control II
Computer Control III
Computer Control IV
Computer Control V
Computer Control VI
Computer Control VII
Computer Control VIII
Computer Control IX
Coincidence Unit
Clock Generator
Control Switches and Logic
Digit Pulse Generators
Engineers Control Panel
Half Adder Type 1
Half Adder Type 2
Main Control Unit
Multiplicand Tank
Memory Units
Multiplier Tank
Order Coder
Order Decoder 1
Order Decoder 2
Order Flashing Unit
Order Tank
Sequence Control Tank

Initial Orders Loader
Timing Control Tank
Tank Address Decoder 0
Tank Address Decoder 1
Tank Address Distribution
Tank Address Flashing Units
Tank Address Decoding Final Stage
Tape Reader
Test Frigs
Transfer Unit


The Complementer/Collater/Distribution Unit III is a composite module. It serves a number of functions, it complements the number from the Multiplicand for the subtract instruction and for subtraction of partial products in multiplies. It also acts to collate the Multiplicand with the Multiplier for the collate instruction (C).

If none of these are required, then it acts to delay the number from the Multiplicand to ensure that the output reaches the adder at the same time as it would have done if it were being complemented.

A further function is to add in any additional ones that have been generated by various parts of the CCU, for example when shifting right, or rounding.

This module is basically that shown in Figure 12 of the Report, but with a lot of additional delays to align pulses and to ensure that the output is in step with that from the Accumulator Shifting Unit as it goes into the Adder.