Orthography
Esperanto eliminates the letters ‹q›, ‹w›, ‹x›, and ‹y› from the 26-letter English alphabet and adds the new letters ‹ĉ›, ‹ĝ›, ‹ĥ›, ‹ĵ›, ‹ŝ› and ‹ŭ›. Ido uses the 26-letter alphabet without changes, substituting digraphs for Esperanto's diacritics. While words in both Ido and Esperanto are spelled exactly as they are pronounced, the presence of digraphs means that Ido does not have the one-to-one correspondence between letters and sounds that Esperanto has. However, Ido's digraphs are more recognizable to speakers of Romance languages and its avoidance of diacritics guarantees that any computer system that supports English could easily be used for Ido.
The Fundamento de Esperanto does allow the use of the digraphs ‹ch›, ‹gh›, ‹hh›, ‹jh›, ‹sh› and the single letter ‹u› instead of the ordinary diacritical letters of Esperanto when those are unavailable. With the advent of computers, another system of surrogate Esperanto writing using ‹cx›, ‹gx›, ‹hx›, ‹jx›, ‹sx› and ‹ux› was introduced. It however remains unofficial.
In general, the letter ĥ in Esperanto becomes h or k in Ido. The letters ĝ and ĵ are merged into j while ĉ, ŝ, ŭ, kz and kv respectively become ch, sh, w, x, and qu.
Read more about this topic: Comparison Between Esperanto And Ido