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Fresh-Faced Recruit
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Aug 17, 2000, 01:55 PM
 
I know how bad it is to disconnect or connect SCSI while the machine is running, is it the same for Serial ports which have a printer and modem connected to them or is it safe to 'plug and play' ?
Why won't OS 9 format floppy disks?
Why does my PM 5500 make a loud fanning noise once in a while?
What is the meaning of life?
Why is the sky blue
     
Professional Poster
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Aug 17, 2000, 02:12 PM
 
the sky is blue because the overwhelming predominance of particles that make up the atmosphere that we perceive as 'blue' are of the same size as is the wavelength of the color blue... this is so, and therefore these particles reflect the wavelength of the color we know as 'blue'

do not pull anything from a serial port when the Mac is powered up.
(ok i stand corrected and am guilty of being too cautious, pull serial devices at will)
what is a floppy disk?

your fan is kicking in as needed to cool your Mac or perhaps the bearings are going out (worn) or perhaps it is not seated properly (loose)

Monty Python explained the meaning of life in full and richly so

[This message has been edited by wlonh (edited 08-22-2000).]
     
Mac Elite
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Aug 22, 2000, 07:44 AM
 
As long as they aren't in use, it's safe to connect or disconnect serial devices to a Mac that's on.
     
Dedicated MacNNer
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Aug 22, 2000, 10:09 AM
 
Safe to disconnect:
Serial Ports = OK
USB = OK
Firewire = OK
Monitor = OK
SCSI = NO!
ADB = NO!

While it is technically possible to "hot-swap" SCSI and ADB devices, you are risking serious damage to your computer if you do so.
     
Mac Elite
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Aug 22, 2000, 04:16 PM
 
Guess I was lucky when accidentially disconnected ADB couple of times...

SCSI is hot swappable, that's what some of the big servers do...or if your SCSI got screwed so bad that you can't boot with it, then hot plug it to re-initialize...but generally, don't even think about it. When I turn off my Yamaha SCSI burner hot, my entire computer freezes...
G4/450, T-bird 1.05GHz, iBook 500, iBook 233...4 different machines, 4 different OSes...(9, 2k, X.1, YDL2.2 respectively) PiA to maintain...
     
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Aug 22, 2000, 04:30 PM
 
big servers maybe so, but notwithstanding that it is a very bad idea to hot swap SCSI on a Mac, ditto ADB, of that i have always been sure...

i know folks that have done bigtime damage to their Macs on both scores
     
Mac Elite
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Aug 22, 2000, 05:14 PM
 
I was under the impression that the unplug mouse->crash Mac was fixed in System 6.

SCSI:
I have never had any problem hot-swapping my scanner (no it is not in any way a useful practice but I am fairly certain it does nothing bad); I have done it on my old Performa and on my new G4 w/ SCSI card. actually, that's not true-I lied. if I unplug the scanner while the scanner software is running and my computer is set to 256 colors, the scanner software crashes. that is the only time.

drives you DO NOT want to turn off while the computer is on if they were on while the computer started up. the computer will porbably crash. However, there is an incredibly useful little utiliy called "Schuzzy" (I believe freeware, from Circus Circuits Software) which can load SCSI drivers and mount SCSI volumes even if the external devices were plugged in/turned on after the computer has started up. when I used this utility, disconnecting my zip drive hot (after removing the disk) did not cause any problems (very useful for sharing 1 zip between 2 computers). I still would not recommend hot-swapping external hard drives, though.
     
Clinically Insane
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Aug 22, 2000, 06:17 PM
 
I think people are being too cautious here... I hot swap ADB and SCSI all the time with my computers on! Never had a problem.
And about the Yamaha freezing when you turn it off hot, never happened to me... what comp you runing it on, what burner etc?

Cipher13
     
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Aug 22, 2000, 06:42 PM
 
Cipher, I'm on G4/450 Rev2.6, with the lattest Firmware/software update for both the G4 and the Yamaha burner. Burner is connected through Adaptec 2930 SCSI card.

I've once hosed a SCSI-2 cable by hot-swapping it, but that was the worst damage ever happened to me...

I'll give "Schuzzy" a try. thx for the recommendation!
G4/450, T-bird 1.05GHz, iBook 500, iBook 233...4 different machines, 4 different OSes...(9, 2k, X.1, YDL2.2 respectively) PiA to maintain...
     
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Aug 22, 2000, 06:57 PM
 
"...given the Mac's aggressive SCSI standpoint (hardware reset vs. Unit Attention), you cannot turn SCSI devices on and off without creating directory code errors on your media. These are low-level directory errors which affect the device partition, and, ultimately, the SCSI driver. They are, unfortunately, not the type of directory problems detectable by tools like Norton Utilities, but they can be determined by using some more obscure SCSI tools and measuring instruments."

"...a few things about the SCSI controller itself, and the idea that hot swapping/power up/down SCSI devices in the chain isn't allowed. While that's a valid point, in practice it's often NOT an issue. Two solutions to the power up issue are: Make sure that a device that might be powered up or down is not the last device on either the internal or external chain. #2… if you're going to be powering devices up and down, after completing use of the powerup device (scanner), make sure to shutdown to nvramclear the SCSI controller instead of a simple restart, which may not clear the controller map."

"The risk of SCSI address damage to the partition map on a drive is real—but the risks depend on a dozen factors. The RF generation is a true real factor, and the termination is simply a "ping" by the controller to detect the time length of the SCSI chain—it will not (or should not) answer or respect any devices located a certain length beyond the calculated length of the SCSI chain. This prevents device echoes from coming back of the terminator (end of wire) and causing erroneous requests to the controller. Adding a hot device at the end of the chain is just dead wrong."

(taken from articles written 2 years ago by F. Keith Bumgarner [formerly?] of MacInformed http://www.macinformed.com/)

i have the archived articles in full should anyone want them...


     
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Aug 22, 2000, 07:00 PM
 
http://til.info.apple.com/techinfo.nsf/artnum/n30935

Swapping ADB devices (unplugging a device cable and replacing with another device cable) while the computer is on is commonly known as hot swapping and is NOT a recommended practice. Doing so may, at the very least, cause erratic behavior such as sluggish or slow performance of the device in question. For instance, mouse movement of the screen pointer may be so slow that it is effectively unusable.

At the worst, hot swapping could damage the ADB controller chip on the Logic Board. The same would hold true for connecting video or SCSI cables while the computer is powered on. Unless the cable technology is specifically designed for hot swapping, such as USB or FireWire, Apple recommends against hot swapping.

[This message has been edited by wlonh (edited 08-22-2000).]
     
Clinically Insane
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Aug 23, 2000, 03:07 AM
 
taken from articles written 2 years ago

Speaks for itself.
Recomendations are seldom right. Perhaps it is dangerous, but after 4 years of hot swapping ADB and SCSI on my 5500, never a problem.
Any computer more modern than 2 yrs old probably is more immune to these problems... even my 4 year old 5500, which predates the writing of the aforementioned articles, has never had troubles with hot swapping those devices.
The worst damage I have done to a SCSI devices have been 1) - blowing up two Yamaha 6416 burners (got them replaced free, hehe), and that was not through hot swapping. It was through plugging them into a Wintel (oops...). and 2) - I don't know how this happened, but it seems I tore a SCSI cable up somehow... must've snagged it when moving it... damn, did that look cool!
Anyway, I will happily continue to hot swap all of my devices, against all recomendations, and don't say "don't say I didn't warn you".
Should something happen, I will post how right everyone was in the Peripherals forum.

Cipher13
     
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Aug 23, 2000, 03:27 AM
 
don't say i didn't warn you!
http://til.info.apple.com/techinfo.nsf/artnum/n30935

my Mac is (GUESS WHAT) two years old!! and i wonder why i NEVER have any trouble with it... no beta NewWorldROM jive is only one reason... another is i do not hot swap that which is not meant to be hot swapped... and i have surely seen others come to great grief over having doen otherwise...

swagger on, pup!

[This message has been edited by wlonh (edited 08-23-2000).]
     
Professional Poster
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Aug 23, 2000, 03:39 AM
 
"Power off all devices prior to changing SCSI chain configuration: Always turn off the Macintosh and all peripherals before attaching or detaching any cables or devices or changing SCSI ID numbers. Doing otherwise could cause permanent physical damage to your computer or SCSI devices as well as the loss of important data"


http://til.info.apple.com/techinfo.nsf/artnum/n9387


another quite recent article:
http://til.info.apple.com/techinfo.nsf/artnum/n58245

Connecting a SCSI Device

1. Shut down your computer and make sure the SCSI device is turned off.

2. Connect one end of a SCSI cable to the SCSI port on your SCSI device.

3. Connect the SCSI adapter that came with your computer, shown below, to the other end of the SCSI cable.

4. Connect the SCSI cable with the adapter attached to the computer's SCSI port or to the last SCSI device already in the chain. IMPORTANT Make sure the last device in the SCSI chain is terminated properly.

5. Turn on all devices in your SCSI chain. Then turn on your computer. IMPORTANT Always turn on all external SCSI devices connected to your computer before turning on the computer itself. Otherwise, your computer won't recognize that the SCSI devices are connected to it and your computer may not be able to start up.

[This message has been edited by wlonh (edited 08-23-2000).]
     
Clinically Insane
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Aug 23, 2000, 05:59 PM
 
IMPORTANT Always turn on all external SCSI devices connected to your computer before turning on the computer itself. Otherwise, your computer won't recognize that the SCSI devices are connected to it and your computer may not be able to start up.

So very untrue... I ALWAYS turn on my burner just before I burn... no problems starting up, and no problems burning. As I have said, these are more disclaimers than anything. You have a problem and complain to Apple, they say "check the TIL. Its all in there... we warned you". There is very little risk on modern computers with modern peripherals. Even on older computers...
Only problem I ever had with a SCSI device was an old 40 meg hard drive (the thing is about 1' wide by 1' deep by 3" high, so that should give you an idea of age...), on my 5500, where it didn't mount the drive if it wasn't on at startup (which makes total sense - not a problem at all actually). If it wasn't on at startup, however, I could mount it using 3rd party software...

Cipher13
     
   
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