Thread: malloc not actually allocating right amount of memory?

I'm taking a course on C (Software/Hardware Interfaces) and we just talked about using malloc in lecture the other day, so i decided to play with it and see how much memory I could allocate before receiving a failure. I made a program which looped a call to malloc that allocated a meg, and counted how many megs it could allocate before failing- but on my 1 gig laptop the final result was that it could allocate 2 gigs before failing o.O

Then I tried the below script to allocate half a gig, and opened Task Manager to see how much memory was actually being taken up, and it was less than a MB

Code:

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

int main()
{

    void *test;
    int megabytes = 512;

        if((test = malloc(1024*1024*megabytes))==0)
        {
            printf("ALLOC FAIL"); fflush(stdout);
        }
        else
        {
            printf("ALLOC SUCCESS");
        }

    while(1)// hangs program so it doesn't close, and can be viewed in task manager
    {

    }

    return 0;
}

Can anyone explain what's going on? TIA

oh and here's the script I originally used (which is a little longer- i used a link list to store all the values, on the off chance there was any sort of auto memory-management system that realized that there where no pointers pointing to the chunks of memory being stored)

Code:

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

typedef struct node
{
    void *dat;
    struct node* next;
} node;

int main()
{
    node *first;
    node *test;

    int count=0;
    int go=1;

    first = (node*)malloc(sizeof(node));
    test = first;

    while(go)
    {
        if((test->dat = malloc(1024*1024))==0)
        {
            printf("ALLOC FAIL at %d mb", count); fflush(stdout);
            go=0;
        }
        else
        {
            test->next = (node*)malloc(sizeof(node));
            test = test->next;
            count+=1;
        }
    }
    while(1){}

    return 0;
}

aaah that makes sense, i forgot that it could allocate to the hard disk! thanks for the responses guys