strace of fwrite

[Guru]

I have written one very basic file write program by fopen/fwrite/
fclose.
That executable i run through strace.

From strace output i observed fwrite uses "write" system call.

Ex-

write(3, "Text String001"..., 4096) = 4096
write(3, "Text String002"..., 4096) = 4096

Here 3 is my open fd for given file.
Here it always writes 4096 bytes

1) My doubt is, this 4096 is default page size/default memory block
size.Exactely what is this 4096 ?