About importing Z80 machine code

Spectaculator allows you to import and export raw Z80 machine code and data directly into and out of the Spectrum's memory.

Raw Z80 machine code can be produced by the SjASMPlus or the excellent Zeus Z80 cross-assemblers.

You can, of course, still use software such as HiSoft's DevPac in the emulated Spectrum. However, it is much easier to write Z80 code using your favourite Windows editor and then use a cross-assembler to assemble it.