Implementation is indeed "king"!
One problem with theoritcal "O-n" notation is "how expensive is an O?"
I remember one of my first programming assignments on 1960's hardware.
We were using wire-wrap technolgy for H/W prototypes.
The basic software task was to sort thousands of punch cards and produce an output.
We had a port of our mainframe code that would run on our lab machine.
But it took 6 hours to run!
It used the minimum number of compares between card images, but it was very,very slow.
Using a bi-directional indexed bubble sort and a fancy merge, I was able to reduce the time from 6 hours to 5 seconds!
That doesn't seem possible, but it was possible.
These ancient machines with 24K words of memory were slow. My coffee pot probably has a faster processor albiet with not as much memory?!
I understood the problem very well.
My code had no O/S or file system.
Essentially, I wrote it on the "bare metal".
Yes, this was a "one trick pony", but it could do its trick very, very well.
I could calculate partial results as the punch cards were read in, while still allowing the card reader to run at full speed.
On the output, I could calcuate results fast enough so that the ancient shuttle line printer ran at a maximum rate.
The 5 second number is the "dead time" when no I/O is happening at the max rate.
In reply to Re^7: Out of Memory when generating large matrix
by Marshall
in thread Out of Memory when generating large matrix
by cathyyihao
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