Question SATA to PATA adapter jumper settings: Master / Slave / Cable Select / ACD - What does ACD do?

Eug

Lifer
Mar 11, 2000
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Hi there.

I'm in the midst of upgrading an ancient Mac Pro. One of the things I added was a SATA Blu-ray drive. Unfortunately, the optical drive bays in the machine support only IDE / PATA, and not SATA. So I ran a SATA cable to the optical drive bay and it works fine in OS X. Unfortunately, it does not work in Windows 10, because the Mac emulates IDE for this and does not support AHCI. (There is an AHCI patch, but for this model it does not work for SATA optical drives.)

So, I'm thinking of buying a SATA to IDE adapter to convert the SATA Blu-ray drive to an IDE drive. The existing DVD-RW drive in the machine is set to cable select, so I presume I would need to do the same on the SATA to IDE adapter. It turns out many such adapters have no jumpers at all, or else jumpers for Master and Slave, but not Cable Select. (I suppose with no jumper maybe some of the latter ones default to cable select but I have no way of confirming that for most of them, since either there are no online manuals or else their manuals don't mention it at all.) I presume I will need to use Cable Select for any new drive.

However, I did find this Startech IDE2SAT2 one which has jumper settings for Master, Slave, Cable Select, and ACD. I have never seen ACD before. I googled it and came up with ATAPI CD-ROM but without any explanation. What does ACD do?

8180VzmZfnL._AC_SL1500_.jpg

I see that in the example picture they have both ACD and Master jumpered. However, their manual makes no mention of this either.
 

Eug

Lifer
Mar 11, 2000
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From the name, I'm guessing this ACD setting emulates an optical drive, but if so, I still don't know what that means.
 

Steltek

Diamond Member
Mar 29, 2001
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The ATAPI command interface that is built into both the PATA and SATA specifications has support for devices that provide functionality beyond that required just by standard hard disks. In the case of an optical drive, for instance, the device would need ATAPI support for an "eject media" command. A tape drive would need ATAPI command support to load and eject tapes, rewind tapes, etc. Those commands could not be passed through to a standard hard drive as the hard drive simply wouldn't know what to do with them.

I suspect that the 'ACD' jumper setting on this device is what is used to tell the system that it is communicating with a non-hard drive device so it knows it can pass on non-hard drive related SCSI commands to the device through the ATAPI interface. That is the reason why the manual states you must have jumpers on both sets of pins for optical devices but not for hard drives.

BTW, from reading reviews, be aware you'll have to provide your own jumper for the 'ACD' pins because the device itself comes from the manufacturer with only a single jumper provided.

The naming convention 'ACD' may also be some excessively vague reference to drive enumeration. I know in FreeBSD, for example, all IDE optical drives are enumerated with names starting with 'ACD' (i.e. dev\acd0, dev\acd1, etc the number corresponds to first, second, third etc. drives).
 
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Eug

Lifer
Mar 11, 2000
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The ATAPI command interface that is built into both the PATA and SATA specifications has support for devices that provide functionality beyond that required just by standard hard disks. In the case of an optical drive, for instance, the device would need ATAPI support for an "eject media" command. A tape drive would need ATAPI command support to load and eject tapes, rewind tapes, etc. Those commands could not be passed through to a standard hard drive as the hard drive simply wouldn't know what to do with them.

I suspect that the 'ACD' jumper setting on this device is what is used to tell the system that it is communicating with a non-hard drive device so it knows it can pass on non-hard drive related SCSI commands to the device through the ATAPI interface. That is the reason why the manual states you must have jumpers on both sets of pins for optical devices but not for hard drives.

BTW, from reading reviews, be aware you'll have to provide your own jumper for the 'ACD' pins because the device itself comes from the manufacturer with only a single jumper provided.

The naming convention 'ACD' may also be some excessively vague reference to drive enumeration. I know in FreeBSD, for example, all IDE optical drives are enumerated with names starting with 'ACD' (i.e. dev\acd0, dev\acd1, etc the number corresponds to first, second, third etc. drives).
Ah yes. Eject command and such. Thanks, that does make sense. I guess I could just try it and see. Luckily I have lots of jumpers lying around from my PC building days to add the ACD jumper.

Note though regarding the manual. I did not see any mention of ACD in the manual. I just noticed the ACD jumper from the picture and wondering what it was for. (Some of the pictures had the master and ACD jumpered, whereas other pictures only had master jumpered.) All the manual mentions is master and slave. It doesn't even mention cable select.

BTW, I contacted Startech and their support representative had no idea what that jumper was for either, so they said they will contact their technical people.
 

Steltek

Diamond Member
Mar 29, 2001
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It is possible that it might work even without the ACD jumper set. It is one of those things you just have to try to see what works, I suspect.

I came across a German version of a user manual that had one sentence at the bottom about putting a jumper on ACD for "DVD compatibility". It wasn't a Startech manual, but it was obviously the same board, so Startech probably doesn't make it but just buys it from a different Chinese manufacturer and relabels it for sale (or, they make it and sell it to other OEMs for them to relabel and sell).

You could also probably get a cheapo bi-directional SATA to IDE/IDE to SATA converter on eBay that doesn't have jumpers (and which will probably work with a DVD drive). If you go that route, make sure to get one that has two SATA ports as they use one SATA port to go only from IDE to SATA, while the other SATA port is used only to go from SATA to IDE. On those adapters, if you use it with an IDE drive the jumpers on the drive MUST be set to master (the manuals, if they even send one, frequently don't tell you that).
 
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Eug

Lifer
Mar 11, 2000
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It is possible that it might work even without the ACD jumper set. It is one of those things you just have to try to see what works, I suspect.

I came across a German version of a user manual that had one sentence at the bottom about putting a jumper on ACD for "DVD compatibility". It wasn't a Startech manual, but it was obviously the same board, so Startech probably doesn't make it but just buys it from a different Chinese manufacturer and relabels it for sale (or, they make it and sell it to other OEMs for them to relabel and sell).
You are correct. Startech technical support was very responsive and I already got an answer today.

Their technical guy said that the ACD jumper is indeed to better emulate optical drives, but typically it is not needed. So the idea is just to try the M/S/CS jumper first but if that doesn’t work, then you can add the ACD jumper and try again.
 

Paperdoc

Platinum Member
Aug 17, 2006
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Regarding your original question on Master or Slave: Any standard IDE port can support up to TWO devices, and thus each must be identified to differentiate.The port MUST have a Master device attached, and IF there is a second device it must be set as a Slave ON THAT PORT.

IF you have TWO IDE ports on the mobo and use each with only ONE device attached, then EACH port MUST have its sole device set to Master. That term applies to a PORT, not to the whole mobo system.

Now, MOST systems that are set up for IDE (PATA) drives use an IDE cable with 80 wires in its ribbon, and THREE connectors on it in total. ONE of these (typically BLUE) goes to the mobo IDE port. ONE (typically BLACK) is on the other end of the cable and should be used for the device set to be the port MASTER. The third connector (typically GREY) in the middle of the cable is for the second device and should be used for the Slave unit. You already have a DVD device on one IDE port that is set to Cable Select. In that mode, the MASTER device is whichever is connected to the Black END connector; the device on the middle Grey connector will be Slave if it also is set to Cable Select.

Does the cable from mobo to the existing IDE DVD unit have that middle Grey connector not currently in use? Then that is what you use to connect to the new adapter board. Otherwise you'd need a second IDE port and cable.

Now, when two devices are on one port and cable, which device is Master does not matter for most things. HOWEVER, the manual for the board recommends that, IF you ever will try to use one of the devices on the IDE port to BOOT from (say, a bootable disk with utilities or an Install Disk for an OS), then that particular drive must be the Master of the IDE port.

So, assuming you are using one IDE port and cable for the two devices, your simplest path when you are not sure whether you can use the Cable Select option with the new unit is this. Change the jumper on the existing DVD drive to Master, and ensure it is plugged into the Black connector on the cable end. Set the jumper on the new adapter board to Slave and connect it to the Grey middle connector on the IDE ribbon cable. This ensures the two devices are identified differently and connected to the normal connetors on the cable. It also ensures that, if ever you are trying to BOOT from an optical disk, you CAN boot from the DVD drive (which is now the IDE port Master), but not from the Blue-Ray unit.