Hard Drive Platter Thicknesses

It should come as no surprise that hard drive platters have different thicknesses:

Hard Drive Platter Thickness

Hard Drive Platter Thickness

The thicker ones measure 1.25 mm, which is near enough to 50 mils to suggest they date back to the Good Old Days. The three thinner ones in the middle are 0.77 mm = 30 mil and could be slightly younger than dirt. There’s more where these came from and I expect more variation on the theme.

The beveled edges make the platters look thinner than they really are; they’re firmly clamped together with no space between them.

As nearly as I can tell, the IBM 350 Disk Storage Unit on the IBM 350 RAMAC had platters about 25 mil thick. Those were two feet in diameter, so they definitely don’t make ’em like they used to!

The thickness wouldn’t matter, except that the OpenSCAD program producing the hub & spacer tabs for the Mood Lights needs to know.


  1. #1 by madbodger on 2015-11-26 - 09:21

    I know those early IBM drives had a giant hub, but 25 mil thick at that diameter? I would have expected thicker platters and more rigidity. I never got to see the platters in those things, but the later removable-pack drives I worked with had much thicker platters (from memory, 100 mil or so).

    • #2 by Ed on 2015-11-27 - 18:52

      I inferred that from a slide in that presentation, but, yeah, you’d think a big platter so thin would flop in the breeze…

  2. #3 by RL on 2015-11-26 - 11:01

    Later IBM disks of similar diameter, like the 1301, were about 1/8″ thick.

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