IBM 689912U Hardware Maintenance Manual - Page 464

Operating system direct to hardware using a direct driver. Direct drivers, which bypass BIOS, have the advantage of faster throughput, but the disadvantage of limited error-handling capability and reduced software and hardware compatibility and flexibility. This method is not used in the IBM PC Series systems. Operating system to BIOS to hardware. This is the recommended way. It's the most flexible because it's independent of the hardware. Applications to operating system to BIOS to hardware. This method is inflexible and operating system dependent. Applications to BIOS to hardware. This method has some flexibility but it is BIOS dependent. Applications to hardware. This method is hardware dependent and very inflexible, however, it is very fast, very efficient, and it has no overhead. Adding adapters to the System When adapters are added to the system, an area in memory has to be allocated to run its programs. This can be done with either hardware switches or software mapping. If there is a conflict in software mapping: The first device to attach to an IRQ, DMA, I/O Address, or RAM location will probably function. The second device will not be found. Standalone diagnostics might function properly because the device that was found is the only device running. Software configuration conflicts occur when: Hardware is configured differently then the software using it expects it to be. Hardware memory address space is in conflict with memory used by the application software. System Resource Conflicts System failures occur when there are system resource conflicts with the: Interrupt Request Queue (IRQ) Direct Memory Access (DMA) I/O Address ROM and RAM Addresses IRQ: Assigns a unique interrupt request line to every I/O device (line numbers range from 0 to 15). Interrupts the processor to force it to service the request. Handles interrupts on a priority basis (low numbers have the highest priority). 454 IBM PC 300/700, IntelliStation Series HMM