Apple OSes and IDE DMA Support?

KFox wishes to get to the core of this particular issue: "I just recently purchased an iBook and I have noticed that even in Jaguar, the system gets choppy from disk I/O. It appears that Mac OS 9 and Mac OS X don't support DMA access for hard drives, even if the drives are initialized in a UDMA mode. Wintel has had support in this area for a long time (since Win95b). Has anyone in the Mac world had any experience with DMA support on hard drives? Is it supported on iBooks? If so, which models?"

Comments

Drive Setup v1.1

[brejc8]

The ChangeLog seems to have added UDMA in version 1.1 and later updated in 1.7 .
Try searching for UDMA Ultra-ATA ATA33/66/100 because DMA doesnt allways show up.

DMA check for your ibook

[TwP]

DISCLAIMER: I have not tried this, but I found a webiste that has ...

Daemon News has a little section on the iBook and DMA. You can see the Darwin boot sequence by holding down the "v" key at startup. Find the section titled "Further Exploration: Das Boot" in the article above and it will tell you how to view the boot messages and other useful tidbits.

IOATAPICDDrive: Using DMA transfers
IOCDDrive drive: MATSHITA, CD-ROM CR-175, rev 5AAE [ATAPI].
IOATAHDDrive: Using DMA transfers
IOHDDrive drive: , TOSHIBA MK3211MAT, rev J1.03 G [ATA].
IOHDDrive media: 6354432 blocks, 512 bytes each, write-enabled.

It appears that this revision-A iBook does indeed have DMA enabled for both the hard drive and the CD-ROM drive.

This does not help you enable your own DMA, but do a search on Google for enabling DMA on FreeBSD style systems. You might find something useful.

Choppy Disk or VM switching out

[Anonymous Coward]

Are you sure it's the disk causing the problem vs delays due to VM switching in and out. There's a memory utility (can't remember name, Memory Tracker or Memory Monitor?) that will beep each time memory is paged in or out (or you could use top if you can interpret the numbers).

I've found it can be pretty easy to use up all free RAM if you have a number of programs open or they leak memory. I've found at times I've had over 2GB of switch files.

This is with 896 MB of RAM, iBooks can be under spec'd in that department.

Re:Choppy Disk or VM switching out

[Golias]

I thought the same thing as the AC when I saw this post. This sounds like more like a VM issue than a "lack of DMA" issue.

I also recently bought an iBook, and the very first thing I did, before I even booted it up, was drop in a bunch more RAM (and my Airport card, while I was in there). I have not experienced the kind of sluggishness you are talking about during disk reads, so that might be what your actual problem is.

OS X is the best OS experience I've ever had, but it is a memory pig. If you have the default RAM in your iBook (probably 128), you are hitting the VM a lot. It's fine if you don't mind a little sluggishness, but memory is cheap now days, so buying more is money well spent. Even another 128 can make a world of difference.

try this

[austad]

# sysctl -a | grep dma

Look for a setting that's related to DMA and set it from 0 to 1 with "sysctl -w". You should be able to place the setting in /etc/sysctl.conf to make it enable it on every boot also.

Unfortunately, I don't have an OSX box to test it on right now, so I can't give you the exact settings. OSX is based on FreeBSD, and FreeBSD enables DMA by default, however, it's possible that apple found a need to disable it by default. Some drive/chipset combos have problems with DMA, and if they were unsure of which brands of drives or chipsets they would be using, disabling it by default would be the safe way to go.