This only applies to Windows, and provides yet another way of speeding up access to a file that is only going to be read. When turned on, all random OPEN file operations result in a local copy being made of the file in the workstation's "TEMP" directory. (It uses the TEMP environment variable definition to locate this directory.) The local copy is then accessed, rather than the network copy. When the file is closed, the local copy is deleted (and any updates to the file are lost!)

The Local Copy option provides nearly as much performance improvement as memory mapping and even loading files into memory, and has the advantage of not requiring any extra physical memory. So it can work just as well with a 100MB file as with a 500K file (provided you have sufficient disk space). As with all of the related schemes for getting around the performance penalty of peer-to-peer shared file access, it makes the most sense in situations where you are going to be accessing a large part, or all, of the file. (It would not make much sense to transfer a 100MB file from the server to the workstation and then only access a few records from it.) Unlike memory mapping and the MEM: device, this technique works with ISAM files as well, and is immune to concerns over how well Windows supports it (since all we ask out of Windows here is the ability to copy a file).