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Disk Drives Explained

Posted by CowboyNeal on from the stuff-to-read dept.

CowboyRobot writes "Magnetic disk drives are one of those things I usually take for granted without thinking about, but I recently realized how little I understood about how they really work. ACM Queue has an article from their 'Storage' issue titled, 'You Don't Know Jack About Disks', which does a very good job of explaining exactly how magnetic disks have evolved since the 70s and how they work today."

3 of 132 comments (clear)

  1. Nintendo Gamecube by rf0 · · Score: 3, Interesting

    It always intresting to see how things work. Nice little thing to add to this is the way Nintendo do copy protection on their disks (although not scritly on topic). Instead of relying on heavy software encryption they went for a nice simple solution. They spin the CD-Rom the wrong way. As such you need special burners if you want to copy it.

    Now thats a neat idea

    Rus

    --
    Cheap UK and US VPS
  2. A bit more history by Mostly+a+lurker · · Score: 4, Interesting
    Although I found the article interesting in terms of the modern developments in PC hard drives, it is a little misleading concerning the overall situation in the 1970s and 1980s.

    To take the IBM mainframe example he quotes: yes, IBM originally used a CKD (count-key-data) architecture and this was still preferred in the late 1970s for highest performance applications. However, in the last 1970s, IBM already provided FBA (fixed block architecture) disk drives such as the 3370. These moved intelligence of disk geometry into the disk controller and were quite easy to program.

    Other mainframe and minicomputer manufacturers had innovative schemes during the early 1980s.

  3. Re:he forgot to mention..... by vadim_t · · Score: 3, Interesting

    You probably mean you used one of those compression programs like Stacker or Double/DriveSpace.

    The problem is that they don't know how much disk space you have, since it depends on the compressability of the data. Sometimes you would need to write something large to the drive, and the installer would tell you that there's not enough space, although it would have fit. That happens because some data compresses really well. A MP3 won't compress at all, but something like a 16 color image might compress really well.

    So, for these cases you can adjust the estimated compression ratio. You tell the program you expect files will compress to 1/8 of their size, and it adjusts the free space estimation. That's all. Data won't compress any better because of it. I saw lots of people setting a huge compression ratio thinking that seeing 10 times more "free space" would somehow let them put 10 times more stuff on it.

    For a demonstration, I made a "32 MB" 1.44MB floppy, and showed how it got full with 2 MB of files.