Does free() really free memory pages of fragmented heap

#include <stdlib.h>
#include <stdio.h>
#include <string.h>

#define QUANTITY 512
// Piece size
#define PIECE (1024*1024)

void *pieces[QUANTITY];

void allocate()
{
    for(size_t i = 0; i < QUANTITY; ++i)
    {
        pieces[i] = malloc(PIECE);
        memset(pieces[i], 0xff, PIECE);
    }
}

void fragment()
{
    for(size_t i = 0; i < QUANTITY; i+=2)
    {
        free(pieces[i]);
        pieces[i] = NULL;
    }
}

void deallocate()
{
    for(size_t i = 0; i < QUANTITY; ++i)
        free(pieces[i]);
}

int main()
{
    // Allocate, fragment and deallocate memory and see
    // if system virtual memory is really freed by deallocation
    for(;;)
    {
        allocate();
        puts("Allocated");
        getchar();
        fragment();
        puts("Fragmented");
        getchar();
        deallocate();
        puts("Deallocated");
        getchar();
    }
    return 0;
}