When you view a document located on an external memory card, iSilo still needs to read whatever parts you access into your handheld's internal memory in order to display the content. Thus there will always be some delay associated with this because reading from the external memory card can be significantly slower than accessing data directly from the handheld's internal memory. However, iSilo employs caching to help minimize this delay.
The greater the amount of free internal memory on your handheld, the better the potential response because iSilo will be able to cache more of those parts of the document that you access. When you first open a document located on an external memory card, you may experience some initial delays that seem to disappear as you continue to use the document. This is because as you use the document, iSilo caches those parts that you use and when you go back to those parts of the document that have already been cached, iSilo will not need to read them into memory again because it will have already cached them in your handheld's internal memory. However, if you have little free internal memory, iSilo will not be able to cache much of the document and so will need to read from the external memory card more often, resulting in a slower response.