KDF9 was built from germanium semiconductors but also used a form of logic based on toroidal tranformers.

Its chief memorable feature was that, instead of having an accumulator, it utilised a pushdown stack so that arithmetic operations operated upon the top two entries in the stack and thus were of zero-address form. This made it a close match to reverse polish notation which was very convenient for compilers. This feature does not seem to have been utilised by later designs. The principal programming language was Algol 60.

	to Bill Finday’s website which includes KDF9 emulator binaries for most mainstream operating systems. The Whetstone Algol system is included, among other KDF9 programs, and the means to write, compile and run your own new ones. Ada source and documentation of the emulator are provided for anyone wishing to make other ports.
	also to David Holdsworth’s collection of original KDF9 software, together with the C source code for a second, O/S independent emulator.