What needs to be done to enable 32 bit I/O transfer mode for (E)IDE disks, on a system running a
2.4 series Linux kernel?

A.
This feature isn’t supported in 2.4 series kernels.

B.
The hdparm utility must be used.

C.
The Linux kernel must be recompiled.

D.
The sysctl utility must be used.

E.
This feature is enabled by default in 2.4 series kernels.

Explanation:
hdparm provides a command line interface to various hard disk ioctls supported by the stock Linux
ATA/IDE device driver subsystem. Some options may work correctly only with the latest kernels.
-d Disable/enable the “using_dma” flag for this drive. This option now works with most
combinations of drives and PCI interfaces which support DMA and which are known to the IDE
driver. It is also a good idea to use the appropriate -X option in combination with -dl to ensure that
the drive itself is programmed for the correct DMA mode, although most BIOSs should do this for
you at boot time. Using DMA nearly always gives the best performance, with fast I/O throughput
and low CPU usage. But there are at least a few configurations of chipsets and drives for which
DMA does not make much of a difference, or may even slow things down (on really messed up
hardware!). Your mileage may vary.