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.
The Linux kernel must be recompiled.

B.
The sysctl utility must be used.

C.
The hdparm utility must be used.

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

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 -d1 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.