First, a word of caution: I am not an IT specailist, just a user.
The "official" translation of "buffer" within IT is "memoria intermedia", but in this case the "memory buffer" would be "la memoria intermedia de la memoria"
I know in Spain "official" translations are used (like "ratón" for mouse, "pinchar" for click, "disco compacto", etc...", but in Latin America we typically leave the technical words in Elnglish or make a fancy technical term from the word in English. Like "Me compré un
compact de Luis Miguel", o "Debes
clickear (o hacer click) en el icono"
I wuold leave "buffer" as "buffer". I have heard it in spoken Spanish at least. So it would be "el buffer de memoria".
About "on-screen grid", "grid" could be "grilla" o "cuadrícula". These are used for example in graphical softwares for the reference grid, snap to the grid, etc... However, I have never used these words to mean "a group of cells in an Excel sheet". In this context, I would use "tabla" o "planilla" (table or spreadsheet). "On-screen" pordría ser "de la pantalla" (of the screen), "en la pantalla" (in the screen), "que se ve en pantalla" (seen on the screen) o "que aparece en pantalla" (that gets displayed on the screen).
How does this sound?
Check the memory buffer and on-screen grid
Verificar el buffer de memoria y la planilla que aparece en pantalla