Chat here about code rewrites, mods, etc... with respect to the github project https://github.com/esp8266/Arduino

Moderator: igrr

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By Frogmore
#22687 Quad IO uses 4 lines for data for up to 4 times the speed of standard.
Dual IO uses 2 lines for data
Standard uses a single line for data

You need to use the mode that the flash part supports. The datasheet for the part should describe the modes that it supports. The HW design also has to have the lines connected.