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Enterprise-class ATA Drives
dfung writes "This has been mindlessly discussed many times before here, but Western Digital has now introduced real enterprise-class ATA drives with SCSI-like performance specs and 30% lower price. So now you can buy a real 10K rpm ATA drive. Interestingly enough, they mention the reason for the traditional difference in price between ATA and SCSI which I never have seen mentioned here - it has to do with testing costs, not controller electronics|platter quality|etc. Another interesting tidbit is that 160 million ATA drives were sold last year. I saw about 2 million of them stacked up in the aisles at Fry's Electronics yesterday, but that sure is a lot of drives."
hmm; don't think of it that way. it's simply not possible for people to go and plug in stuff by hand on a cable and test them. usually. that's wayyyyyyy in the end anyway - intergration testing in software people's terms?
;). after each "scan burst" you toggle the clock, and sequentially read out all the registers to see if the chip did what you wanted it to do.
I would *suspect* that scsi chipsets have more things to be tested than ATA ones, since as you may notice, they are supposed to work with 15 devices OR by themselves, possibly providing onboard termination or not.
testing often starts at the wafer stage (where each chip is probed and marked, failed ones are crushed, oftenly), and again when chips are packaged - usually speed sorted / repaird (if possible - a lot of memory devices support repair) at this time. After that, integration testing is actually EASIER because this is when you have a whole set of firmware commands to work with, etc.
Frequently chips have dedicated testing commands, though (that you don't get to know), so things are not completely dire. most flash memory have test modes, for example, where if you put in a code sequence it will write the entire array into, say, a checker board pattern. This is to avoid massive delays of half microsecond writing each location, sequentially. Logic chips (like, say, scsi chipsets) usually have a different challenge - they have embedded subsections, often cache, that you don't have access to directly.
now, to get "into the chip" you will have to sequentially put in the test patterns / vectors into special registers that reside on the lines that run between each embedded component. one register at a time (usually sequentially through a few (dozen or less) pins. testing is expensive, but pins more so
this gets back to the scsi being harder to test - probably the control chipsets are more complex. I can't imagine the mechanical sections being any different (besides the 15krpm ones, anyhow) - generally when something have to communicate with a bunch of other things (like scsi) versus just a few (ATA), the former is more pain in the butt testing wise.
oh, btw - more PIN is also another factor to costs. testers have a limited number of pins, so if you have more pins to test, you test less per turn. can't speak authoratatively on the pincount of drive controller chipsets... just FYI here.
side note: one thing you realize after being in testing is that semiconductor manufacturs often (or, sometimes - depending on the manufacture) puts a LOT of margin into their chips. when they say the chip is rated 75 degrees C, they really mean 75 degrees because the chip was TESTED at that temperature.
ok. long rant... gotta stop now.
My life in the land of the rising sun.
It is always interesting to see all the jumping through hoops to defend the use of SCSI. But I think it is all bullshit.
Every manufacturer could, at any time, start producing a diskdrive that has the mechanical and head/servo electronics of an existing SCSI drive integrated with an ATA bus interface. It would have the reliability of the SCSI drive, and assuming that manufacturer has experience in ATA electronics there is no reason to assume that it would have problems on that end.
No need to have it in the market for 5 years to prove reliability. Disk drives are not even in the market for such a long time.
No, they just want to sepatate two different price categories and don't want to blur that gap by offering drives with features from both sides.