[C言語]getchar()関数は,1文字入力する毎に処理が走る訳ではない

#inculde <stdio.h>
 
int main( void )
{
    int data;
 
    while( 1 ) {
        // １文字入力
        data = getchar();
        if ( data == EOF ) {
            break;
        }
 
        // 入力された文字を出力
        putchar( data );
    }
 
}

$ gcc echoback.c -o echoback
 
$ ./echoback 
123
123
^d
 
$

gcc -g echoback.c -o echoback
 
gdb echoback
GNU gdb (Ubuntu/Linaro 7.3-0ubuntu2) 7.3-2011.08
Copyright (C) 2011 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "i686-linux-gnu".
For bug reporting instructions, please see:
<http://bugs.launchpad.net/gdb-linaro/>...
Reading symbols from /home/user1/work/echoback...done.
(gdb) list
1   #include<stdio.h>
2   
3   int main( void )
4   {
5       int data;
6   
7       while( 1 ) {
8           // １文字入力
9           data = getchar();
10          if ( data == EOF ) {
 
 
(gdb) b 7                                               #ブレークポイントを7行目にセット
Breakpoint 1 at 0x804841d: file echoback.c, line 7.
(gdb) run
Starting program: /home/user1/work/echoback 
 
Breakpoint 1, main () at echoback.c:9
9           data = getchar();                           #キー入力待ち. 
                                                        #"123Enter"を入力するまで進まない
(gdb) next
123
10          if ( data == EOF ) {
(gdb) next
15          putchar( data );                            #1文字目の出力
(gdb) next
16      }
(gdb) next
 
Breakpoint 1, main () at echoback.c:9
9           data = getchar();                           #ここではキー入力待ちにならない
(gdb) next
10          if ( data == EOF ) {
(gdb) next
15          putchar( data );                            #2文字目の出力
(gdb) next
16      }
(gdb) next
 
Breakpoint 1, main () at echoback.c:9
9           data = getchar();
(gdb) next
10          if ( data == EOF ) {
(gdb) next
15          putchar( data );                            #3文字目の出力
(gdb) next
16      }
(gdb) next
 
Breakpoint 1, main () at echoback.c:9
9           data = getchar();
(gdb) next
10          if ( data == EOF ) {
(gdb) next
15          putchar( data );                            #4文字目の出力(Enter)
(gdb) next
123                                                     #ここで纏めて文字が表示される
16      }
(gdb) next
 
Breakpoint 1, main () at echoback.c:9
9           data = getchar();                           #再度入力待ち
(gdb) nex
Ambiguous command "nex": next, nexti.
(gdb) next