Instruction set
An instruction set refers to the repertoire of instructions provided by any particular CPU architecture.
Also a key part of an instruction set are the means provided for indicating sources and destinations for data processed by those instruction, the addressing modes of the instruction set. For example, some early machines only included a single register, the accumulator, and were otherwise a load-store architecture; eventually provision for multiple registers became common. Also, it is now common for instructions to be able to use a stack as the source or destination for data.
Some early computers used the alternative term order code for the instruction set (and order for instruction). This was more common in the UK; especially at Cambridge (on the EDSAC, and descendants such as the LEO). In the US, uses included several Lincoln Laboratory computers.
