A device for biopsy of body tissue. The keyboard includes a light channeling membrane and key members constructed at least partially of translucent material so that light produced from a light source is channeled upwardly to the upper surfaces of the key members. The present invention recognizes that a fast router has small routing table cache that has a high hit ratio and that a high hit ratio can be achieved with a small routing table cache by predicting which entries will be needed in the routing table cache in the future and by populating the routing table cache with those entries before they are needed. Using symbolic simulation, the variables are applied to a decompressor to obtain the symbolic expressions. The second type of database key may correspond to a record in the database and the second type of database key can be a unique value.