What is S.M.A.R.T. and how to read S.M.A.R.T. attributes

Question

Read the bottom for updated information/amendments
Hi everyone,
S.M.A.R.T. is Self-Monitoring, Analysis and Reporting Technology.
[size=15]1. S.M.A.R.T. info websites[/size]
OK, now we all know what S.M.A.R.T. stands for. For more details about S.M.A.R.T., here is a comprehensive non-technical explanation about S.M.A.R.T. by pcguide.com. Maxtor has published a white paper on S.M.A.R.T. too. And this is from Seagate. Anyhow, I am not going to discuss whether S.M.A.R.T will protect your harddisk from failure, etc etc here. Let us focus more on S.M.A.R.T. itself.
[size=15]2. S.M.A.R.T. monitoring tools[/size]
S.M.A.R.T. data is stored as a tabulated data somewhere in the harddisk as registers. The tools below support reading these registers value from S.M.A.R.T. enabled harddisk.
1. SpeedFan *sign-up is required for download, but it's FREE
2. Active SMART
3. Sisoftware SANDRA 2002.6.8.97 SP1 , older version doesn't support
[size=15]3. S.M.A.R.T. Tabulated Information[/size]
Here is a screenshot captured with SpeedFan.
Let us go through the screenshot. As can be seen, there are 5 columns - Attribute, Value, Worst, Warn and Raw.
Attribute
describes the meaning of the values. As mentioned above, the SMART data is stored as a tabulated data as registers. Each attribute represents one register ID. eg Raw Read Error Rate is register ID 01, register ID 03 is Spin-up Time, etc.
Note that the register IDs are not displayed by SpeedFan, but are displayed by other SANDRA and Active SMART. I have no idea how many S.M.A.R.T. attributes are there, Active SMART stated it can detect more than 35 attributes!
However, some attributes are manufacturer specific. So possibly some attribute names as shown in these SMART tools might not represent the true meaning of the values too!!
Value
is the current relative value of the attribute read from the registers.
Worst
is the worst value ever achieved.
Warn
is the critical threshold value of the attribute. If the Value has reached and OVER this threshold value, with very high probability the harddisk is in trouble. If SMART is enabled in the BIOS, SMART will alert user in the POST screen, with some manufacturer specific error code. You may need to refer to your manufacturer then.
Note : Value, Worst and Warn are all relative values, such as percentage, not actual count. I have no idea how to calculate these values. This is the very S.M.A.R.T. algorithm, isn't it? ?(
Raw
is in fact, the most understandable represented value here! It represents the actual count of the attribute. SpeedFan displays this raw value as hexadecimal numbers. Such as Power On Hours Count is "AA8", which is 2728 in decimal numbers, meaning that the harddisk has been power on for 2728 hours!! There are some Raws represent average rate, such as "CRC Error Rate" etc.
[size=15]4. S.M.A.R.T. Attributes In Detail[/size]
Hopefully by now, you have the basic idea how to read the tabulated data. I will try my best to go through the attributes one-by-one, which after that shall make you understand more about S.M.A.R.T. and of course, starts to appreciate it.
Raw Read Error Rate represents the condition of the physical disk, based on raw (physical) read errors, and physical surface defects.
Spin Up Time is the time taken for the hdd to spin-up. more info
Start/Stop Count is the number of counts (cycles) the hdd start/stop. more info
Reallocated Sector Count - the number of sectors have been reallocated. Surface scan and found bad sector will increase this count. Now this drive has 7 bad sectors already!
Seek Error Rate - how often the drive failed to locate the data (seeking)
Power On Hours Count - the number of hours you have powered on the HDD.
Spin Retry Count - how many time your drive need to attempt to get the drive platter spinning. If this value is more than 1, your drive is seriously in very bad condition!
Calibration Retry Count - represents the number of time your drive perform calibration retry. I am not sure if low-level format would increase this value.
Power Cycle CountThe number of time the hdd has been powered on. On and Off = 1 cycle.
Read Soft Error Rate - should be Soft Read Error Rate. Similar to Raw Read Error Rate but this one depends on logical level, such as error occured in the hdd buffer, etc.
Temperature - The drive temperature, Forget the relative values, read from the Raw value -- "2D" in this example, which is 45C. But my SpeedFan displayed 47C at that time!! SpeedFan seems to produce some +-2C error from actual reading once in a while. :P
Hardware ECC Recovered is the number of counts ECC correction is performed on the data.
Reallocated Event Count - similar to Reallocated Sector Count but this one is on the data.
Current Pending Sector - is the number of counts how many sectors are currently pending. But what is a pending sector?? ?( ?(
Offline Correctable - which is Off-line Scan Uncorrectable Sector Count. Again, what is off-line scan?
UltraATA CRC Error Rate - which is in fact, CRC Error Count instead of rate. As shown, there have been "3C3", which is 883 errors occured already!!!
There are more S.M.A.R.T. attributes, such as
Thoroughput Performance - again, this relative value is surely got from some wierd algorithm again.
Seek Time Performance - some algorithm has been used to calculate this performance value.
Power Off Retract and Load Cycle Count are IBM HDD specific features -- unload the head off the platters when power off. More info on Head Load/unload cycle.
[size=15]5. SpeedFan S.M.A.R.T. Fitness and Performance bars[/size]
I should not comment on this too much because this is Almico's work. I am not sure how he calculate to define the "fitness" and "performance" though. It could probably based on mathematic relation between the current Values  and the threshold Warns.  
For most hdds, like Maxtor and Seagate's, out-of-the-box the fitness bar has already reaching half-way 50%. But for IBM hdd, the fitness bar is always around 100%. This is because IBM hdd has its threshold/Warn values set to unrealistically high until it's quite unreachable even after a long term use. While for other brand HDDs, the threshold values are more realistic. Thus, the fitness bar in particular, does not tell the true fitness of the HDD. Take it as a reference only. Please always refer back to the Raw values to determine the fitness.
[size=15]6. Conclusion : Judging HDD fitness by our own selves![/size]
Now we all know what the Attributes are, so roughly everyone will have the basic idea how to judge HDD health by our own selves depend on the attributes you're reading. S.M.A.R.T. itself however, define "fitness" and "performance" based on its own algorithm.
We can categorize the attributes into :
Error Related Attributes
"UltraATA CRC Error Rate", "Raw Read Error Rate", "Raw Soft Error Rate", "Hardware ECC Recovered Count", "Reallocated Sector Count", "Reallocated Event/Data Count", Offline Correctable"
-- tell how often are those errors occured. For the above example, this Maxtor harddisk should be RMA-ed for its high CRC Error Rate count.
Drive Fitness Attributes
Spin Up Time, Start/Stop Count, Seek Error Rate, Power On Hours Count, Spin Retry Count, Calibration Retry Count, Power Cycle Count, Power Off Retract Count, Load Cycle Count
-- check "spin retry count" and "Seek Error Rate", any value other than zero is really bad.
Other Attributes
I have no idea what they are for except Temperature.
As the conclusion, understanding S.M.A.R.T. attributes helps in knowing your HDD fitness by your own self, rather than waiting for the S.M.A.R.T. to alert you for severe error. That might be too late already.  8o
Thanks for reading.
Edited:
1. for better reading pleasure
2. added Conclusion
3. added explanations about SpeedFan SMART Fitness and Performance bar.

Answer 1

Quote
Originally posted by WarLord
I like this HD tool. i use it everyday now. the tempture readings are great Hd temp cpu temp and even the system temp nice added feature to the monitoring. And this is an alternative to enabling the SMART in the bios? Thats the way im understanding it. is that right Maesus ?Because i have disabled in bios. She went threw alot of trouble here. thank you  
Well from my observation, whether SMART is disabled or enabled in the BIOS, SMART is always working within the HDD itself.
Basically SMART is acting like a blackbox, monitoring and tabulating HDD condition from time to time and its attributes only fully revealable by the manufacturers. SpeedFan's SMART status only displays partial information that is displayable. Some attributes are hidden, ~OR~ the attributes' locations are different from one HDD to another brand, such that some values don't correspond to the attribute meaning at all.
It is very doubtful to claim that enabling SMART in the BIOS will hog down the performance. Just like a transport bus (yeah real bus that fetch passenger :P ), with or without the black box installed can't help it if the driver wants to speeding. :P