On Sat, 23 Nov 2002 13:58:22 -0600, Nathan E Norman <[EMAIL PROTECTED]> wrote:
>On Sat, Nov 23, 2002 at 03:39:32AM +0000, Pigeon wrote: >> OK, but what about the hard drive? In both cases the head has to track >> over the preceding sectors and switch into write mode when it gets to >> the right sector to be written. OK, so one's magnetic, one's optical, >> but the head servos are doing the same thing. The spiral track on a CD >> means you basically have to "pick the track up" a few rotations behind >> where you need to start writing so you've got time to sync in; not a >> problem. And it's the same problem as starting a new session on a >> multisession CD, or packet writing. It's only gonna be awkward if the >> laser drive is so screwed that it burns garbage for the first few >> sectors after you put it into write mode. > >HDDs have concentric tracks. CDs have spiral tracks. Therefore, >tracking on a CD platter is harder. The head servos are not doing the >same thing. I know. This makes it harder; it makes it slower; it doesn't mean you can't do it, and the difference between doing it and not doing it is software, not hardware. >HDDs spin at a much higher rate than do CDs. Therefore, latency is >not as big of an issue with HDDs. And the head servos - and head drive and the hardware in general - has an easier time. You win some, you lose some. >HDDs read and write magnetic ones or zeroes. If you "screw up" and >reverse the sense of a bit on an HDD, you can repair[1] it. Not >possible on a CD-R[2]. AFAIK the HDD doesn't generally know that it's flipped the wrong bit until it tries to read that sector and gets a CRC error. That's when your filesystem flags an error and you wish you'd made a backup. If the bit is not on a sector that the drive was in process of writing anyway, it has no way of correcting it. It might be in some other file altogether. So yes, you can repair it, but I don't think this is automatic, transparent or part of normal operation. >You claim it's a simple matter of backing up and picking up where you >left off. On an HDD this is trivial; you simply wait for your sector >to come round again. On a CD you have _one chance_ to "pick up where >you left off"; if you miss it you can't wait for the CD to spin round >again; the track is a spiral! You must again backtrack and try to >find the next sector. If you "miss" and start in the wrong place, you >are screwed. This is pretty much what I said, but you're not "screwed" because of the spiral track, it just takes longer to have another go. This means that the app that's writing to the drive has to wait around, but it's not a problem for the drive itself. As I said, it's only gonna be a problem if the laser drive is so up the spout that it writes garbage for the first few sectors after going into write mode - which is highly unlikely, or multisession/packet writing would be pretty much impossible, in fact any writing would be hard, and to design a laser drive like that would be harder than designing a proper one. >I am reminded of a quote: Never attribute to malice that which can be >described by sheer incompetence. Hardware manufacturers are always >producing junk; for the most part the market corrects these flaws. I have repaired so many TVs that have failed after a few years because of poor build quality that I have maybe a more cynical viewpoint on this. They fail for stupid reasons; poor quality solder connections, inadequately rated components, failure to allow for thermal expansion of hot-running parts, using a switch rated at 3A to pass a 10A surge. If the market corrected flaws, the build quality of TV sets would improve. It doesn't; it gets worse. Especially where technical equipment is concerned, the market is too ignorant to recognise that the manufacturers are producing junk. I get loads of puzzled looks when I explain to someone that the fact that they paid x grand for their TV doesn't affect the fact that it has failed because it is a badly-made pile of shite, and that any TV they buy for any price from any manufacturer is going to be a badly-made pile of shite; people just don't want to believe it. Manufacturers produce junk so that the technically ignorant market is forced to keep buying junk over and over again. The non-ignorant form too small a percentage of the market to have a significant effect, and are forced to buy junk because there's nothing else. This may be less true of the computer market but it is still true enough and especially so where CD writers are concerned. The main market for CD writers is for home users to copy music and playstation games etc. This is the same market that is responsible for the appearance of PCs with bulgy plastic front panels that make it hard to get your fingers to the floppy drive, transparent cases with flashing lights inside and Windows XP. This is the market that would read this thread and not understand a word of it. This is not a market that will naturally correct flaws without having the hardware manufacturers keep other flaws up their sleeve. Heck, the whole computer market is based on one big rip-off, getting both individuals and businesses to buy new machines and new versions of Windoze every few months, constantly "upgrading" and never getting any more functionality - why do you need a 2GHz CPU for word processing? That never even occurs to most buyers. I could go on, but I'd start talking about the car industry and get even further off topic. 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