Read only hard drive 1

[soundmonkey]

I am trying to build a forensic workstation for a course. IT has two removable ide bays and a fixed ide drive. I need to make one of the removable drive bays read only, or if possible switchable between read only and RW. Is is a simple matter of putting a switch on pin 25 of the IDE cable or is it more complicated than that?

 

[Peahippo]

This is a great question, and I'm keen on getting an answer also.

According to

http://www.pcguide.com/ref/hdd/if/ide/confSig-c.html,

most of the 40 pins on the IDE/ATA cable are used for something, but it's not obvious which one or ones can be switched off (or more likely, held high (+5v) or low (ground)) to make the hdd usable for only reads and not writes.

You mentioned pin 25, which is DIOR:-HDMARDY:HSTROBE ... but I don't know what that means. DIOR probably means "data input/output ready", which is clear enough. But the DIOR line seems to have two sub-definitions:

-HDMARDY: low hard disk "MA" ready. Once connected to ground, the signal is enabled. I don't know what MA means; perhaps some memory-access reference.

HSTROBE: high H strobe. Likely it tells the controller on the hdd that data is ready to be cycled ("strobed&quot into it from the cable's data lines. Once connected to +5v, the signal is enabled.

DIOR may not be a good signal to monkey with, since we need to convince the hdd that it's OK to output, but not to input. DIOR seems to be blind to the difference between input and output.

It may also be possible to set the hdd partition as read-only, but I'd have to investigate further.

Can anyone find a link for the definitions of the signals? The signal names given in the above link are ambiguous as to their function.

 

[soundmonkey]

I meant pin 23 which I have down as the IO write. pin 25 is IO read.

 

[Peahippo]

Pin 23 is defined as "-DIOW: STOP". To me, this means we would have to hold the signal line high (+5v) to avoid the write of data into the drive.

Now, I'm assuming the IDE/ATA interface uses +5vc/0vdc for its signalling. I would need to confirm that before ever applying voltages of any kind to wires or pins on the cable.

But if it is simply a constant +5vdc on the line, then you have to face the challenge of breaking open the cable run somewhere along the line in order to inject +5vdc into it (into the drive ... not into the controller).

IDE cables are cheap, and I suggest you use some 5h1tty old IDE drive that has no value ... many of the sub-1GB ones fit into this category. (I took a 130MB drive out of production the other day ... it's a perfect candidate for such experimentation.)

First figure out which cable line is pin 23. Chances are, with one side of the cable being marked in red for pin 1, then 23 will be the 23rd wire over from that.

Once found, take a razor and slice a section of the wire free from the cable. Cut that across the middle and note which end goes to the drive. Strip the insulation from that end (note that this wire is tiny and this will require exacting work to avoid cutting the conductor again), and then solder on a long red wire, like the kind used in the power lines coming out of your power supply. For info:

http://www.pcguide.com/ref/power/sup/parts_Drive.htm.

Take one of your spare power plugs and stick the other end of the red wire into it at the point of the plug's own red wire. To make the red wire fit into the plug snugly, strip a longer length than normal and then fold the exposed wire in half to make a double-wide wire end. Cram it in there good.

Viola! You have now hard-wired your IDE drive to always be write-disabled. What happens now, I really don't know. After all, the controller will still try to set -DIOW low and expect the hard disk to do the write operation. Rough signalling aside, the hard drive's controlling logic may respond to the IDE controller in some way that involves other signals, like along the data lines themselves ... and if that's not right, the IDE controller may consider the drive to have failed in some way.

 

[bcastner]

How about doing it in software?

http://www.gotpackets.com/rdd/rddindex.htm

 

[Peahippo]

RDD sems to only "restrict" those drives that are added to the current system, not those already existing in the system. The use of the words new/newly is conspicuous in the product.

But you have a point ... we can put the geeky hardware mods aside and ask if there is a software solution. Personally, I'd find out the controller chip used on the motherboard, and then surf the manufacturer's website for utilities. I assume that the manufacturer best knows the features of the controller, and may have built in all sorts of nifty features, like write-protection.

Hey, soundmonkey: What's the make and model of the IDE controller on your motherboard?