As you know, when the ATA PC card is inserted in your MC10000, all of the designs are displayed as icons on the screen. In versions of the MC10000 prior to 2.2, each time you touched the "page turn" keys there was a noticeable delay while the machine created thumbnail images for each design on that page of the card. Effective with 2.2, each time a card is inserted in the machine, there is a period of "hourglass" activity, during which all of the designs have thumbnails created. Those images are stored on the card as files of type .jbf. This makes turning the pages go much faster. The .jbf files cannot be used in any way on the PC. You can delete them, but they will be recreated the next time the card is placed in the machine. Since they consume very little space, this is not much of a burden and it does make using the machine go a bit faster.