Since there are USB thumb drives and hard drives...

shetlineshetline
Posted:
in Current Mac Hardware edited January 2014
...why does Target Disk Mode (let's call it TDM for short) depend on Firewire? TDM first went away with the MacBook Air, and now we've lost TDM for the latest non-pro Macbooks.



Since I don't think Apple would invite all of the subsequent grief caused by the lack of TDM if USB were an easy out for more or less the same job, what is it that I'm missing?

Comments

  • Reply 1 of 5
    MarvinMarvin Posts: 15,326moderator
    USB 2 is a host-based protocol, firewire is peer-to-peer. Although there is an active computer in the equation, it may not be possible to give direct access to the internal drive from USB without the hard drive's controlling host active.



    The fact that Apple haven't done it already doesn't imply it can't be done because PPC machines weren't able to boot over USB and that functionality was introduced with the Intel machines. It may be the case they just haven't bothered making it possible. After all, they were trying to promote the use of firewire in every way they could.



    Actually, it doesn't seem like it would be a limit due to the protocol. If the USB drivers are loaded and the OS can see this at boot time then the OS can reach a state where it can read/write the internal drive with an active USB connection. Maybe TDM over USB will do this in a firmware update.
  • Reply 2 of 5
    anaahlawyanaahlawy Posts: 20member
    So would the rumored use of ethernet cable solve this problem? If so, would it be of higher or lower speed than the firewire (400 or 800)?
  • Reply 3 of 5
    futurepastnowfuturepastnow Posts: 1,772member
    Quote:
    Originally Posted by Marvin View Post


    USB 2 is a host-based protocol, firewire is peer-to-peer. Although there is an active computer in the equation, it may not be possible to give direct access to the internal drive from USB without the hard drive's controlling host active.



    The fact that Apple haven't done it already doesn't imply it can't be done because PPC machines weren't able to boot over USB and that functionality was introduced with the Intel machines. It may be the case they just haven't bothered making it possible. After all, they were trying to promote the use of firewire in every way they could.



    Actually, it doesn't seem like it would be a limit due to the protocol. If the USB drivers are loaded and the OS can see this at boot time then the OS can reach a state where it can read/write the internal drive with an active USB connection. Maybe TDM over USB will do this in a firmware update.



    Well, if you break open an external drive case, there's obviously a little controller chip in there that makes it work as the non-computer end of a USB connection. I'm sure Apple could include such hardware, probably at little cost, and the ability to power it without fully booting the machine it's in.



    I have no idea if it would be possible to do this without extra hardware, with only EFI in control of things. But I'm sure someone at Apple knows.
  • Reply 4 of 5
    sequitursequitur Posts: 1,910member
    A friend bought a new Mac from an Apple Store awhile back and they transferred his info from the old to the new Mac. Do they still do that? If so, I wonder how they do it.
  • Reply 5 of 5
    futurepastnowfuturepastnow Posts: 1,772member
    Quote:
    Originally Posted by sequitur View Post


    A friend bought a new Mac from an Apple Store awhile back and they transferred his info from the old to the new Mac. Do they still do that? If so, I wonder how they do it.



    Probably Ethernet. That's easy to do. Or if the old Mac has 10.5, you can just use the Time Machine backup to transfer everything.
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