Mac Daniel's Advice

Hot Swap or Not?

Charlie Ruggiero - 2001.02.28

Q: Recently I read about how FireWire and USB on newer Macs are hot swappable (this means you can unplug and re-plug devices while the computer is on). I am confused, because I thought that serial and ADB connections on older Macs were hot swappable as well. I have swapped out both connections without problems.

A: This, as I remember, was a hotly debated subject between various experts in the field. When it all comes down to it, there is not a clear cut answer for all the older connections.

Serial (modem and printer ports) on older Macs is considered by most (including me) to be hot swappable. I have swapped thousands of serial devices with no problems I could detect. To be careful, you should always do what Apple says. As a general rule, you should only swap devices when they are not being accessed. You can cause problems with FireWire and USB if you unplug them while data is being transferred. Serial is the same way: If you are transferring data via local talk or through a modem unplugging the device or cable could cause data corruption. I would not expect this to cause hardware damage, however.

ADB in my opinion, is not hot swappable. I have seen many people swap keyboards and mice with no problems, but I have also seen the ADB port become dead because of this very same thing. Although rare, hardware damage can occur to both your computer's port and the devices you plug in. It is best to shut down your computer before swapping any kind of ADB devices. After all, data corruption is far less serious than hardware damage (especially if you back up your data frequently).

Update: ADB is hot swappable on the PowerBook G3 Series (WallStreet).

SCSI (not considering some advanced server SCSI solutions) is not hot swappable. You can cause serious damage to hardware and data by unplugging and re-plugging SCSI cables and devices.

Headphone/Speaker Jack is hot swappable to a point. I say this because a lot of people use speakers. Be sure to turn your speakers down or off before you plug them into this port. When the metal touches the back it could cause a pop, which, if the speakers are turned up enough, can break the speakers.

Monitor port is sometimes considered to not be hot swappable, but I have never seen damage from someone plugging in a monitor after the computer has started up. If I do unplug or plug in a monitor after the computer is on I always make sure the monitor is off before doing so. If you want to be on the safe side, shut down your computer before unplugging your monitor cable. Sometimes when you plug in a monitor after you turn on the computer, you will not be able to set a resolution above the default. To fix this, just restart with the cable already in.

Floppy port (like on the Mac Plus) is not hot swappable.

Ethernet (this includes the various different connection types) is always hot swappable. If it was not, then every time your computer lost a network connection there could be damage.

Modem connections are the same as Ethernet.

S-Video in/out and composite (RCA) video in/out are hot swappable. These connections are similar to those you would find on your VCR and DVD players.

The bottom line is that you do not know always shut down and do your cable swapping. Incorrect use of hardware is not covered by your warranty, so always follow Apple's recommendation (which you can find either in your manual or in their vast tech-info archives).

Charlie Ruggiero has used a lot of Macs, from Plus to G4, and even ran a BBS (remember those?) on a Plus. He works as Macintosh tech support and technology advisor for the College of Education at Michigan State University. He does a lot of hardware and software troubleshooting, as well as a great deal of video editing, capture, and streaming. Charlie is well versed in HyperCard, fairly knowledgeable in Future Basic, and has a good background in sound and video. He even has his own site, Edge of Heaven.

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