Serial reads one character at a time from the input.
It places those characters, one at a time, into an input buffer - the size of which depends on the Arduino you are using.
You then read those characters from the input buffer using the Serial.read() function, which returns the characters from the buffer one at a time.
If you want to read more than one at a time you can use the Serial.readBytes(buffer,len) function to read up to "len" characters from the serial buffer into the memory pointer to by "buffer":
- that will read 9 bytes into the variable "buf", leaving room for one extra character for the null-termination for the string.