Thanks Tom! You answered my questions. Thanks!
Please see my other post as to what some of my machines are doing. As for your comment on never having a problem with using DMA access on CD-ROMs before, under any version of Windows, I have to wonder how I could have been working with the wrong systems and system makers in the past. ;-) I never could get Win 95-98 to accept this setting as of up to a few years ago, when I was actively providing close systems for sale. Now, I see on my XP machine that it allowed one of my CD-RWs to go that way, but not the newer DVD. Maybe its really all a matter of the mobo's I have been using recently, and the fact that much of my stuff has long since been called "state of the art". My reference to "just using an IRQ to gain the attention of the CPU?" is just my slang description for what an IRQ does. Interrupts are nothing more than exclusive (most of the time) doorways to speaking to the CPU. However, using DMA is not always possible, even if allowed to do so. Windows 98 SE has an aversion to disabling the use of an IRQ in your BIOS for your video card. It will word, but also become unstable and sometimes not allow the system to properly shut-down. This is most obviously a Windows-problem, not a hardware one, but this is my past and where I am coming from. I probably should have helped you some by being more specific on asking what DMA will do for a CD-ROM-like device. I am aware of the speed increase and the by-passing the CPU. I really wasn't asking for the definition of the terms, but the results and reliability of doing this. My mistake. I should have been more clear. As for the Linux info, thanks a lot! That's really helpful stuff. I will also check the on-line docs and do some research on it. I will have to play with my Linux box to see if DMA access is enabled for the slower, older CD-RW drive it has in it and if it performs properly. I am really looking forward to all the neat things that I can do in Linux that Windows always hid from me. ;-) Thanks again for response. T Tom Brinkman wrote: > On Monday September 30 2002 09:26 am, Technoslick wrote: > >>Tom, >> >>Your comments bring up a question... >> >>In Windows, enabling DMA for CD-ROMs (and it variants) is considered >>a 'no-no' and will cause problems most every time. In many cases, >>Windows will automatically deactivate it if you set it on. How is it >>different in the Linux O/S, and what advantages are received by using >>Direct Memory Access in Linux over just using an IRQ to gain the >>attention of the CPU? > > > DMA has to do with faster disk IO. I don't know what you mean by > "just using an IRQ to gain the attention of the CPU?" On my mobo, as > with most all of 'em, the ide1 (second ide) is on IRQ 15. Enabling or > disabling DMA doesn't change this. IO improvement such as DMA is very > important since all drives, ide or scsi run on the 33 mhz PCI bus. Also > PIO modes (no DMA) go thru the cpu, DMA bypasses the cpu and does data > tranfers directly to memory. > > The various types of DMA, eg, for my CD drive, (hdparm -i) > UDMA modes: udma0 udma1 *udma2, employ some gimmicks to improve goin > thru the 33 mhz PCI bus. Much the same as AGP compared to PCI for > video. Therorectically AGP doubles it from 33 to 66 mhz, actually it > provides less than 10% boost. It's more important for disk IO tho. > While udma2 might get 12mb/sec, udma5 will get around 40mb/sec (hdparm > -t). 'Course that's for harddrives. Enabling DMA for Cd drives won't be > near as much, but it's still better than without it .... if your > hardware is capable. > > From 'info hdparm' > "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." > > I dual boot W98 (rarely ;), it sets all my drives including my CD > drives to DMA. I can't remember any Windoze version or combo of > hardware I've used in the past that didn't enable DMA. I do remember > some Winsux burning software that disabled DMA, but that's a software > deficiency. > > As to "How is it different in the Linux O/S". Memory access, > management and VM in Linux is much different than in Windoze. It's also > a moving target, with newer Linux kernels striving to constantly > improve it. Google "linux memory management", or search the kernel > mailing list. This might be a good place to start http://linux-mm.org/ > > > ------------------------------------------------------------------------ > > Want to buy your Pack or Services from MandrakeSoft? > Go to http://www.mandrakestore.com
Want to buy your Pack or Services from MandrakeSoft? Go to http://www.mandrakestore.com
