This dialog is used for configuration of two IDE disk drivers:
  1. IBM1S506.ADD is the IBM driver which is shipped with &os2;. IBM has updated this driver quite a number of times. A newer driver is required for OS/2 Warp 3 and 4 if you wish to use hard disks which are larger than 8 MB.

    With this driver, many of the dialog items are disabled because they are only used with DANIS506.ADD (below).

  2. DANIS506.ADD is a replacement driver written by Daniela Engert. It is 99% command-line compatible with the IBM driver, but has added lots of enhancements. Since the IBM drivers cannot enable busmastering support with many of the newer chipsets, it is strongly recommended to use this enhanced driver, which can greatly enhance hard disk performance. Also, this driver allows to to configure your hard disk controllers in much more detail to resolve problems with your system setups.
Detailed help for each of the settings is available in the form of fly-over help (tooltips). Put your mouse pointer over a dialog item and wait for about a second, and an informational text will come up.

It is however necessary to understand in general that both drivers differentiate between three type of options:

  1. Global options affect operation in general. Those are on the top left of the dialog and include settings like startup messages and (with DANIS506.ADD) how hardware is searched at bootup.

  2. Adapter settings affect one adapter (controller) only. With the IDE and EIDE bus system, there is one adapter for two hard disk units. Computers usually have two adapters built in, so this makes a total of four units which can be connected to a standard computer. In the dialog, adapter options are on the bottom left.

    With both the IBM1S506.ADD and the DANIS506.ADD drivers, adapter settings must be specified only after an /A:x option, with x specifying the adapter to be configured by all the following options (either 0 or 1). The dialog will add this option automatically if you change any adapter parameter from a non-default value. All the settings in the "Adapter (controller) settings" group therefore affect only the adapter which is currently selected in the "Current adapter" group.

    Each adapter needs a few system resources such as an interrupt (IRQ), a Direct Memory Access (DMA) channel, and port addresses (base address) for data interchange between the adapter and the computer. If these options are not set, the driver uses defaults which work on most systems.

    See the remarks below for details about bus-mastering (DMA) support.

  3. Unit settings affect one unit (hard disk) only. Each adapter can have two units, which are commonly dubbed as "Master" and "Slave". In the dialog, unit options are in the right half.

    With both the IBM1S506.ADD and the DANIS506.ADD drivers, unit settings must be specified only after an /A:x option first (which specifies the adapter) and a /U:x option next (which specifies the unit in the adapter), with x being 0 or 1 each time. The dialog will add these options automatically if you change any unit parameter from a non-default value. All the settings in the "Unit (drive) settings" group therefore affect only the unit which is currently selected in the "Current unit" group.

Busmastering, Direct Memory Access (DMA). Modern hardware allows the EIDE controllers to read and write data directly from main memory without any help from the main processor. This greatly enhances disk performance because while data is exchanged with the disk, the processor can do something else.

While the older Programmed I/O (PIO) modes 3 and 4 still required control by the main processor, the EIDE standard introduced several multi-word DMA modes. In those modes, the drive takes over control of the bus (bus-mastering) and places data directly into the main memory (DMA). The standard IBM1S506.ADD fails to recognize many chipsets and can thus not enable busmastering on many systems. DANIS506.ADD does a much better job at this and still allows you to fine-tune the detection process.

Ultra-DMA is yet another extension of the original DMA protocol. Previously, data transfers took place only on the rising edge of the strobe signal. Ultra DMA modifies the protocol to allow data to be sent on the falling edge of the strobe signal as well, thus doubling the data transfer rate. Also, because of the increased danger of data corruption, error detection was added. As a result, Ultra-DMA is both faster and safer than regular DMA or plain PIO.

DMA with hard disks can cause problems on some hardware however. This can be due to older controller hardware which cannot handle this at all, or bad cables which cause too much noise on the bus so data is corrupted at higher speed. Also, many older drives cannot handle DMA well or only at lower speed. For this reason, busmastering can be disabled totally or (with DANIS506.ADD) limited to a fixed data rate.

The adapter /BM setting enables or disables busmastering for a whole adapter (that is, both units which are connected to that adapter). This option has been available in all versions of IBM1S506.ADD and is supported by DANIS506.ADD as well.

The unit /BM setting enables or disables busmastering for one unit only. This option is only available in newer versions of IBM1S506.ADD and is supported by DANIS506.ADD as well.

With DANIS506.ADD, you can also limit the data rate for a certain unit by explicitly specifying the protocol to use.