Bits 12 and 1 of the interrupt registers are assigned to disk interrupts. Bit 12, DSKSYN, indicates that the sync register matches disk data. This bit generates a level 5 interrupt . Bit 1, DSKBLK, indicates "disk block finished." It is used to indicate that the specified disk DMA task that you have requested has been completed. This bit generates a level 1 interrupt . More information about disk data transfer and interrupts may be found in Chapter 8, "Interface Hardware."