[Macpartners] Re: Macpartners Digest, Vol 17, Issue 4

[Kerem B Limon]

Quoting "John C. Welch" <jwelch at MIT.EDU>:

> On 10/8/04 12:28 PM, "Kerem B Limon" <k_limon at MIT.EDU> wrote:
> 
> > In the interest of accuracy, I'll note that this is not what I am talking
> > about.
> > And I am not trying to state a flame war, but perhaps offer some feedback.
> > 
> > High-end PC motherboards also have diagnostics LEDs on-board, too, and PC
> > motherboards have practically *always* had diagnostic POST error codes and
> > beeps courtesy of the various IBM-compatible BIOSs since I can remember.
> This
> > may be a useful tool for the tinkerer or those of us who open up our
> machines.
> > It's good to see that Apple has adopted this trend. This, however, does
> not
> > help the average user or the tech who's trying to help them over the
> phone.
> > 
> 
> And unless you spent the money on third party hard cards, most of them
> amounted to "bad stuff, you're screwed". The ironic thing is that Apple had
> better post codes than most, but getting them translated took an act of
> God/Steve, or you had to know someone.

Actually, that is not accurate. Award, AMI, Phoenix, and IBM BIOSs (OK, even
Compaq BIOS) have always had a very detailed list of useful error codes,
including beep-sequences (a la Morse code) that can be looked up in a reference
table that would definitively indicate the failure mode. And this information
has been publicly available since before PCsauruses roamed the Internet.

> 
> > What I am talking about, however, is a hard drive access light or LED.
> Every
> > PC
> > since the first IBM compatibles have had this; this is an invaluable tool
> for
> > telling--without opening up anything--whether your computer is accessing
> the
> > hard drive or not. While old tools under OS 9 like Norton Disk Light may
> try
> > to
> > implement this in software, there is nothing like a hard-wired indicator
> like
> > this without regard to what OS is running on the machine. I've even
> soldered
> > LEDs to the hard drive pins (OK, I made a connector, fine) and slotted an
> LED
> > in some of my Apple cases for this very reason.
> 
> Again, on a machine with an active swap process, this is not going to be
> that useful. In fact, I'll say it's pretty much a feel-good light. If your
> boot drive isn't able to be accessed, there's a really handy
> indication...you can't boot.

See my comments in my reply to your previous message about how the hard drive
LED, whilst a binary indicator, can convey a multitude of information. Coupled
with when and how this information is conveyed, you can distinguish various
failure modes. In this case, you would most likely see a stuck HDD LED on a PC
and the POST would hang or timeout, indicating an electronically broken or
misconfigured HDD. Also, it is relatively easy to distinguish regular access
patterns (background noise) from unusual behavior (signal), even with a simple
on/off LED.

> 
> If it's a dead partition on the same drive, but you can get to your boot
> drive, the LED says "Stuff is happening", but since you can use your boot
> drive, you kind of expect that, since you're using the drive.

Again, more useful information available with an HDD LED. Obviously I have
booted. I am having trouble accessing stuff on this partition--hey, the HDD LED
is getting stuck solid on! Maybe it's not my software, there's something on the
partition there.

> 
> If it's a dead secondary drive, that's simple too, it won't mount. The light
> is ONLY telling you that *something* is happening. Not if it's good or bad.
> However, a bit of observation will tell you that. If the drive head motor
> has completely died, the light will be useless since a) you won't be able to
> access the drive *anyway* and the light will only tell you that nothing is
> happening, since they don't tell you that the spindle motor is okay, but the
> head motor is dead and gone.

Again, I've booted I presume, and we can't access secondary drive. The secondary
hasn't mounted and when I try to use a disk mounting tool or partitioning
utility, I cannot see the drive and/or the LED gets stuck if I see it and am
having trouble accessing it. I know what/how it's failing.

> 
> In Janet's case...she can tell the drive is running, since she booted off of
> it. What is the light going to do in this case...."Yes, just in case you
> didn't trust the booting bit, your hard drive arm is swinging back and forth
> like Britney Spears' hindquarters".

She can tell if it is something to do with the hard drive or software/OS (i.e.
media vs. software). She opens the folder, the drive starts accessing
vigorously (perhaps not as much as Mrs. Spears) and then gets stuck on. It's
probably a corrupt sector coinciding with a bit of a file that contains
directory/index info or some metadata stream that gets accessed when the
directory listing is done. On the other hand, the drive accesses, the freeze
does happen, but HDD activity ceases--it's a hung process or thread, most
likely, due to perhaps some corrupted binary. Or perhaps the LED goes into
overdrive, flickering wildly and thrashing--perhaps the software is trying to
do the 'wrong thing'? Is it trying to access something unnecessarily? Is there
something else running?

> 
> When hard drives weren't a requirement for function, the light made sense.
> It makes sense in a headless situation, since you may want to just visually
> check without logging into the machine remotely.
> But when you're booting off the drive, it's redundant and silly. If you have
> your CPU unit out of immediate visual range, it's not immediately useful
> anyway.

You've narrowed down the case to a desktop or workstation, obviously not
headless. With cable limitations the way they are, how far from visual range
can the computer be, anyway? Certainly not far with the case of an iMac! And
since when is it more troubling to take a peek at the box those rare (ahem)
times you run into trouble as compared to opening up your box and trying to
make sense of diagnostic LEDs?

> 
> > 
> > Have you ever put your hand on a floppy drive or laptop to 'feel' if the
> hard
> > drive was spinning? Since Apple makes an effort to d--esign ultra-quiet
> hardware
> > (not a bad thing in and of itself), lack of audio feedback on top of other
> > indicators makes it even harder to tell what's going on inside the machine
> if
> > your display/screen is on the fritz!
> 
> If your display or screen is on the fritz, you're probably not doing much
> with the machine at that point.

"display/screen" here in context meaning the GUI/UI is stuck or not responding
and not the hardware itself failing per se.

> 
> john
> 
> 
> -- 
> Yeah, I know Sid Vicious wore a lock on a chain around his neck just like
> that. But the first time you try and pogo with that thing on it¹s gonna chip
> a tooth, Road Warrior.
> 
> 
> 
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Kerem

Kerem B. Limon
kerem.limon at mit.edu /e-mail