Hi Margaret, SGIO would avoid this issue under Windows. But is it really an issue? I would argue that maybe a large OS cache is still beneficial in the case you highlight. While there is time wasted in flushing the cache's contents for output, there is time saved by reading the file from the cache for input. And intuitively (I haven't benchmarked it), the time saved by not reading the file from disk (very slow medium) is probably greater than the time used to flush the RAM cache (very faster medium). So yes, step2 is slower than step one, but all the RAM still makes step2 faster than if there was nor RAM cache at all. No? I did a lot of benchmarks on direct IO and buffers when using SAS data sets in http://www.amazon.com/High-Performance-SAS-Coding-Christian-Graffeuille/dp/1512397490