Why can a bad device connected to a motherboard crash a mac during OS X runtime and not during start

[rodion15]

There's something I'm confused about:

Why can a bad device connected to a motherboard (such as a wifi card, optical drive, hard drive, etc) crash a mac during OS X runtime and not during startup?

According to apple troubleshooters in Apple-GSX, a Kernel Panic or System crash may be produced by a bad device, so that to diagnose it Apple advises you to: 1: start off a known good OS X volume such as an external hard drive (this would mostly rule out software) and if the problem continues 2: disconnect as many cables as possible from the motherboard/logic board: WIFI card, hard drives, optical drive, Card reader etc. and then test it like that (using an external monitor and external hard drive).

My doubt is: What does apple exactly mean by a system crash? I understand it's a freeze or kernel panic during OS X execution and not an spontaneous restart during start up (before logging in), in fact, apple calls these crashes during startup "intermittent shutdown".

In fact, if the unhealthy restart occurs during startup, the apple troubleshooter doesn't advise you to remove all those device cables and test. Instead it simply asks you the typical pram and smc resets then try with an external drive.

Why can a bad device connected to a motherboard crash a mac after log-on and not during startup? In what way can a defective device produce a crash?

 

[DelJo63]

I would think the crash occurs on first access AND that's not happening a boot time.
That would rule out kb, mouse, video, audio. On our mac, I see the switch become active before the logon screen, so I think ethernet(wired) can be ruled out too.

What you got?

 

[rodion15]

I would think the crash occurs on first access AND that's not happening a boot time.
That would rule out kb, mouse, video, audio. On our mac, I see the switch become active before the logon screen, so I think ethernet(wired) can be ruled out too.

What you got?

Hi jobeard, good to read you again,
sorry but I don't get your first paragraph, what do you mean with "switch".
My doubt is how can a bad device connected to a motherboard crash a mac after log-on and not during startup? In what way can a defective device produce a crash?

 

[DelJo63]

sorry but I don't get your first paragraph, what do you mean with "switch".

A switch is like a router

My doubt is how can a bad device connected to a motherboard crash a mac after log-on and not during startup?

Crash is (guessing here) on first access of the device and this device is not being accessed @ boot time

In what way can a defective device produce a crash?

A bad driver not compatible with your OS level

 

[cliffordcooley]

I can only guess a self diagnostic during bootup, doesn't account for all runtime scenarios. And that there is a runtime error causing the crash.

Example:
Memory modules passing self-diag test at boot, but then causes a BSOD or system freeze an hour later.

 

[rodion15]

I've edited my original test a little, I've added that the troubleshooter asks you first start off an external hard drive thus ruling out software and then if the crashes continue to remove all possible devices and retest.

What jobeard says above "it's first access to a device that produces the crash" seems to make sense, so a faulty device such as a wireless card may crash the machine. I don't know what a system crash is really, why does the machine freeze or restart?

 

[rodion15]

I can only guess a self diagnostic during bootup, doesn't account for all runtime scenarios. And that there is a runtime error causing the crash.

Example:
Memory modules passing self-diag test at boot, but then causes a BSOD or system freeze an hour later.

Thanks mate, that seems right.