That's a hugely broad definition of critical, enough to encompass most of business and finance software.

Sure. But is there far more critical COBOL than C out there?

The OS kernel for nearly every PC and server on earth is written in C.

Almost every electronic device on earth complicated enough to require software is probably running at least some firmware written in C.

I think those both outnumber ATMs by a hefty margin.

take a look at VMS to behold how elegantly and seamlessly we wrote software in whichever language suited the task most appropriately, barely conscious of the concept of foreign functions being a horror story for future generations instead of being entirely standard and letting us switch from BLISS to Pascal to ADA and C and C++ and DEC BASIC and throw in a few DCL macros or optimize the compilers to which source was of course provided and so that's how we delivered really rather efficient programs, really, in LOC, since nobody was hammering square pegs into semantic round holes or chasing effects when you needed to manage types intrinsically to your critical path routines but didn't need to extend the type system throughout your code base because RDB quaintly would let you call it in FORTRAN and get down to typology from the elements of mathematical sets themselves if you must, nicely isolated and ACID wrapped with system wide cluster transaction management available for everything and everyone's needs and the filesystem designed orthogonal to the database letting you think of your data in a single unified concept with primordial os level guarantee of data integrity for corollary sanity checking