Getting back to DMA mode in Windows XP

CD-ROM and DVD-ROM dri­ves can revert to using PIO mode, despite being set to use "DMA if Avail­able." Here's how to make Win­dows XP rede­tect the DMA capa­bil­i­ties of the drives.

CD-ROM and DVD-ROM dri­ves can revert to using PIO mode, despite being set to use "DMA if Avail­able." Here's how to make Win­dows XP rede­tect the DMA capa­bil­i­ties of the drives.

This behav­iour occurs with the fol­low­ing conditions:

• Win­dows XP is the oper­at­ing system
• A CD-ROM or DVD-ROM drive, which is known to sup­port DMA mode now works only in PIO mode.
• The drive con­troller is set to use "DMA if avail­able" but reports to be only in PIO mode.

Fol­low­ing is the mech­a­nism that has worked for me, please try it at your own risk, it involves hack­ing the registry:

1. Open RegEdit
2. Find the fol­low­ing KEY:
   HKEY_LOCAL_MACHINESYSTEMCurrentControlSetControl
   Class{4D36E96A-E325-11CE-BFC1-08002BE10318}00x
3. The last four dig­its will be 0000, 0001, 0002, 0003, and so on.
4. Under each key, delete all occurences of the fol­low­ing values:
   Mas­terId­Dat­aCheck­sum
   SlaveIdDataChecksum
5. Reboot the com­puter. Win­dows will now rede­tect DMA settings.

Trala! If that doesn't do it, please check the very use­ful com­ment below by a user named STARK.