hi i bought this cd writer and i used it after 5 months its read speed was very low "needs about 40 min to copy 700 mb cd" so what is the problem when i bought it it work fine
You are not by any chance running Windows XP?Check that DMA is enabled for the drive (do this by entering the device manager and check properties for your IDE channels). If you can't enable DMA from Windows (it's common) then delete the IDE channels and reboot.
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And yes, DMA should definately be enabled or else performance will take a serious hit.
If the issues mentioned above don't work out for you, your drive might be having problems with certain discs (are they perhaps dirty?) or suffering from a filthy lens.