You donu2019t. In C code double x 1234.5678 fwrite x sizeofdouble 1 fd u2026there I wrote 8 bytes at once.At the lowest level of the hardware the interface between the CPU and thehard drive controller might take 4 or 8 bits at a time but that reallydoesnu2019t matter.That said There is one VERY good reason to split up a write like the oneabove and that is if the file is going to be shared between computers of adifferent kind.Some computers store numbers with the leastsignificant bytes first in memoryand others with the mostsignificant bytes first these are called u201cLittleEndianu201d and u201cBig Endianu201d machinesu2026after a story in Gulliveru2019s Travelsu2026which isespecially amusing to read in light of this.If you write all 4 bytes of an u201cintu201d variable in one chunk like this int x 0x12345678 fwrite x sizeofint 1 fd u2026and read it back on a machine which has different u201cEndiannessu201d to the onethat write it like this int x fread x sizeofint 1 fd printf 08Xn x u2026then itu2019ll come out as 0x78563412 All the bytes being in the reverseorder.If you think this might happen then you have to be much more careful int x 0x12345678 putc x 0xFF fd putc x8 0xFF fd putc x16 0xFF fd putc x24 0xFF fd u2026and read it back int x x getc fd x x getc fd 8 x x getc fd 16 x x getc fd 24 u2026in other words forceable write out in this case the low order byte firstand make sure you read it back in the same order.