fread() optimization binary file

I am reading a 40 MB file with three different ways. But the first one is way faster than the 2 others. Do you guys have an idea why ? I would rather implement condition in loops or whiles to separate data than load everything with the first quick method and separate them then - memory saving -

   LL=10000000;

   fseek(fid,startbytes, 'bof');

   %%Read all at once %%%%%%%%%%%%%%%%%%%%%%
   tic
   AA(:,1)=int32(fread(fid,LL,'int32'));
   toc
   %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

   fseek(fid,startbytes,'bof');

   %%Read all using WHILE loop %%%%%%%%%%%%%
   tic
   i=0;
   AA2=int32(zeros(LL,1));
   while i<LL
      i=i+1;
      AA2(i,1)=fread(fid,1,'int32');      
   end
   toc 
   %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

   fseek(fid,startbytes,'bof');

   %%Read all using FOR loop %%%%%%%%%%%%%%%
   tic
   AA3=int32(zeros(LL,1));
   for i=1:LL
      AA3(i,1)=fread(fid,1,'int32');      
   end
   toc 
   %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

Elapsed time is 0.312916 seconds.

Elapsed time is 138.811520 seconds.

Elapsed time is 116.799286 seconds.

Answer 1

[Walter Roberson]

Consider reading data in chunks (e.g., 4 Kb): that should give you better speed than reading single int32 at a time, but would also reduce the amount of memory needed.