file input with readLines

More on my previous question ...

I have put in timing statements to try to get a better idea of where the
problem is, like so:

conn<-file('filename','r')

for (chunk in 1:100000) {
? print(paste('begin read at',date()))
? Lines<-readLines(conn,n=25)
? print(paste('begin processing at',date()))
?# process "Lines"
? print(paste('end loop at',date()))
}

Every time I go through the loop, all the date() functions return
*exactly* the same time! ?It *looks like* it runs through each iteration
very quickly and then takes longer and longer to simply start the next
iteration. ?I don't believe this. ?I think R must be doing some kind of
latency trick or something. ?But, anyway, the point is that I was
assuming the problem was in the I/O, and now I don't know if it's I/O or
processing. ?Either way, I don't understand it and would really
appreciate some wisdom from you guys.

Thanks.