Hello James, JT> to add additional features, but other zip programs won't be able to JT> interpret this data so very little is actually gained by using this JT> approach. I disagree. If you have backwards compatibility that means your new format can still write to suit current decompressors _if need be_. If you invent a totally new format you are likely to end up with 'just another format' which might end up relegated to the bin like so many others in the past have been. Was not the RAR format superior to ZIP? The only reason for not maintaining compliance with ZIP is that if the ZIP file header construct prohibits you from including the main shortcomings we have been speaking about. Once again IMHO, Al+