how to write and read file fastly?

I have one data translation device of which I am getting data using 'getdata' function. now I have to save this data and once it saved I have to read it again and plot a graph. I am getting data using following code [d,t]=getdata(ai); // where d is data and t is time data1=d(:,1); data2=d(:,2);

I have to save this data very fast and again read it and plot graph. which method shall I use?? xslread and write or csvread and write or dlmread and write?

[Walter Roberson]

Duplicated by later http://uk.mathworks.com/matlabcentral/answers/272052-how-to-write-and-read-file-fastly which has an answer