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{{From|https://help.ubuntu.com/community/DMA}} {{Languages|UbuntuHelp:DMA}} {{Translator|yiding.he}} === 介绍 === 如果你感觉你的 DVD 播放时有跳跃现象,或者拷贝音乐 CD 非常慢,或者在访问光驱时系统变慢,这可能是由于你没有启用 DMA,或者叫“内存直接访问(Direct Memory Access)”。DMA 能让硬盘或光驱等设备直接访问系统内存。Ubuntu 6.06 (Dapper Drake) 能够识别支持 DMA 的设备并自动启用 DMA。 [[Image:IconWarning3.png]] '''警告:'''启用 DMA 在某些情况下是有风险的,这通常跟硬件故障或使用了系统不支持的设置有关。'''不当的使用 hdparm 命令可能导致主要数据的破坏和/或丢失!近 4 年内的系统大都支持 DMA。''' === 启用 DMA === To enable DMA, you need to use the <code><nowiki>hdparm</nowiki></code> command and the configuration file <code><nowiki>hdparm.conf</nowiki></code>. These instructions assume that you are trying to enable DMA on `hdc`, usually the CD-rom drive. # See the what the settings are on `/dev/hdc` <pre>sudo hdparm /dev/hdc </pre> # If you get a line like <code><nowiki>using_dma = 1 (on)</nowiki></code>, DMA is already enabled. Skip to step 4 to see if it has been enabled at boot time. # Enable DMA on `/dev/hdc` <pre>sudo hdparm -d1 /dev/hdc </pre> # You have now enabled DMA for the drive. However, in order for the settings to be automatically applied at boot there you need to edit the <code><nowiki>/etc/hdparm.conf</nowiki></code> script. To do this use this command: <code><nowiki>gksudo gedit /etc/hdparm.conf</nowiki></code> Add the following to the end of your hdparm.conf <pre>/dev/hdc { dma = on } </pre> (another way of avoiding editing of the hdparm.conf file is to simply run <code><nowiki>sudo hdparm -d1 -k1 /dev/hdc</nowiki></code> to keep the DMA flag). === 常见问题 === If your drives are configured in [Cable Select] mode and while running `hdparm` commands you receive errors related to timeouts or drive not ready, try changing the drive to be a master or slave device depending on your system configuration. This does require opening the case and as far as I know most drives are set to Cable Select from the manufacturer. Sometimes step 3 above can fail with an "Operation Not Permitted" message. You can fix this by editing the file /etc/modules: For an Intel CPU put the lines <pre>piix ide-core </pre> above the line <code><nowiki>ide-cd</nowiki></code> For an AMD CPU put the line <code><nowiki>amd74xx</nowiki></code> above <code><nowiki>ide-cd</nowiki></code> For a VIA Chipset put <code><nowiki>via82cxxx</nowiki></code> above <code><nowiki>ide-cd</nowiki></code> Then reboot and try steps 3-4 again.... === Further reading === The hdparm has further options that may be more risky. They can be seen using the <code><nowiki>man hdparm</nowiki></code> command in the terminal. For a detailed description of DMA visit the IEEE http://standards.ieee.org/reading/ieee/std_public/description/busarch/1212.1-1993_desc.html IDE, EIDE and UDMA http://www.spcug.org/reviews/bl0108.htm ---- [[Category:CategoryDocumentation]] [[Category:UbuntuHelp]]
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