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Head Sliders

Hard Drives 101: Magnetic Storage
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The term slider describes the body of material that supports the actual drive head. The slider is what actually floats or slides over the surface of the disk, carrying the head at the correct distance from the medium for reading and writing. Older sliders resemble a trimaran, with two outboard pods that float along the surface of the disk media and a central “hull” portion that actually carries the head and read/write gap. The figure below shows a typical mini slider. Note that the actual head, with the read/write gap, is on the trailing end of the slider.

The underside of a typical head mini slider.The underside of a typical head mini slider.

The trend toward smaller and smaller form factor drives has forced sliders to become smaller as well. The typical Mini-Winchester slider design was about 4 mm x 3.2 mm x 0.86 mm in size. Most head manufacturers have since shifted to smaller Micro, Nano, Pico, or Femto sliders. The Femto sliders in use today are extremely small—about the size of the ball in the tip of a ballpoint pen. Pico and Femto sliders are assembled by using flex interconnect cable (FIC) and chip on ceramic (COC) technologies that enable the process to be completely automated.

The table below shows the characteristics of the various types of sliders used in hard disk drives.

Hard Disk Drive Slider Types
SliderYear IntroducedRelative SizeLength (mm)Width (mm)Height (mm)Mass Type (mg)
Mini1980
100%
4.00
3.20
0.86
55.0
Micro1986
70%
2.80
2.24
0.60
16.2
Nano
(+ Pressure)
1991
62%
2.50
1.70
0.43
7.8
Nano
(- Pressure)
1994
50%
2.00
1.60
0.435.9
Pico
1997
30%
1.25
1.00
0.30
1.6
Femto
2003
20%
0.7
0.7
0.23
0.6


Smaller sliders reduce the mass carried at the end of the head actuator arms, which provides increased acceleration and deceleration, thus leading to faster seek times. The smaller sliders also require less surface area, allowing the head to track closer to the outer and inner diameters, thus increasing the usable area of the disk platters. Further, the smaller slider contact area reduces the slight wear on the platter surface that occurs during normal startup and spindown of the drive platters. The figure below shows a magnified photo of a Femto slider mounted on the head gimbal assembly, which is on the end of the head actuator arm.

Magnified head gimbal assembly featuring a Femto slider. (Photo courtesy Hitachi Global Storage Technologies.)Magnified head gimbal assembly featuring a Femto slider. (Photo courtesy Hitachi Global Storage Technologies.)

The newer slider designs also have specially modified surface patterns that are designed to maintain the same floating height above the disk surface, whether the slider is positioned above the inner or outer cylinders. Conventional sliders would increase or decrease their floating heights considerably according to the velocity of the disk surface traveling beneath them. Above the outer cylinders, the velocity and floating height would be higher. This arrangement is undesirable in newer drives that use zoned bit recording, in which the bit density is the same on all the cylinders. When the bit density is uniform throughout the drive, the head floating height should also be relatively constant for maximum performance. Special textured surface patterns and manufacturing techniques enable the sliders to float at a much more consistent height, making them ideal for zoned bit recording drives.

A typical Femto air-bearing slider surface design is shown below.

Femto air-bearing slider surface design.Femto air-bearing slider surface design.

A Femto slider has three distinct areas with complex shapes designed to achieve a consistent head-to-disk floating height across the disk as well as minimal height loss under high-altitude (low-pressure) conditions. The shallow etch area creates a stepped air inlet allowing airflow to create a positive pressure under the air-bearing surface that lifts the slider away from the disk. The deep etch area creates an opposite negative pressure pocket that simultaneously pulls the slider closer to the disk surface. The combination of positive and negative pressures is designed to balance the force of the suspension arm pushing the slider toward the disk, while keeping the slider at the desired floating height away from the disk surface. The balance of positive and negative pressures stabilizes and reduces the floating height variations commonly found in older slider designs. The first drive using the Femto slider design was the Hitachi 7K60 2 1/2-inch drive released in May 2003. Most of the higher-capacity drives on the market today use this design.

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  • 4 Hide
    SteelCity1981 , August 31, 2011 5:44 AM
    Wow very, very interesting article to say the least.
  • 8 Hide
    soccerdocks , August 31, 2011 6:30 AM
    "Density initially grew at a rate of about 25% per year (doubling every four years)"

    If density grows at 25% per year it would actually double in just barely over 3 years. At 4 years it would be 144% greater.
  • 1 Hide
    joytech22 , August 31, 2011 11:22 AM
    Quote:
    when passed over magnetic flux transitions.

    I somehow expected "Flux capacitors" instead.
  • -7 Hide
    johnners2981 , August 31, 2011 12:20 PM
    soccerdocks"Density initially grew at a rate of about 25% per year (doubling every four years)"If density grows at 25% per year it would actually double in just barely over 3 years. At 4 years it would be 144% greater.


    No you're wrong, how embarrassing :) . You're using compound interest. Quit trying to be a smartass
  • 4 Hide
    Device Unknown , August 31, 2011 12:53 PM
    johnners2981No you're wrong, how embarrassing . You're using compound interest. Quit trying to be a smartass


    I'm no math guy, in fact i suck at it, but I see his point, why wouldn't it be compound? and even at compound interest is 144 still accurate? please enplane
  • 9 Hide
    soo-nah-mee , August 31, 2011 3:05 PM
    I believe soccerdocks is right - example...
    Beginning value: 10
    After one year: 12.5
    After two years: 15.625
    After three years: 19.531 (Almost double)
    After four years: 24.41
  • -8 Hide
    johnners2981 , August 31, 2011 3:08 PM
    Device UnknownI'm no math guy, in fact i suck at it, but I see his point, why wouldn't it be compound? and even at compound interest is 144 still accurate? please enplane


    Please enplane??? Compound interest is used to calculate interest and not things like density.
    They were right in saying "doubling every four years" and he was trying to correct them when there was no need so showed him who's boss, oh yeah
  • -7 Hide
    johnners2981 , August 31, 2011 3:10 PM
    soo-nah-meeI believe soccerdocks is right - example...Beginning value: 10After one year: 12.5After two years: 15.625After three years: 19.531 (Almost double)After four years: 24.41


    His calculation is right not the application, why is he using compound interest to calculate the percentage increase in density? It doesn't make sense.
  • 6 Hide
    soo-nah-mee , August 31, 2011 3:13 PM
    johnners2981His calculation is right not the application, why is he using compound interest to calculate the percentage increase in density? It doesn't make sense.
    It's not compound "interest", but it is compounding. If you say something increases 25% each year, you can't just keep adding 25% of the original value! Silly.
  • 2 Hide
    striker410 , August 31, 2011 3:24 PM
    soo-nah-meeIt's not compound "interest", but it is compounding. If you say something increases 25% each year, you can't just keep adding 25% of the original value! Silly.

    I agree with the others on this one. Since it's adding 25% each year, it is compound. You are thinking of it from the wrong angle.
  • 2 Hide
    asymetriccircle , August 31, 2011 4:17 PM
    ok i dont know all this interest shenanigans, but that first diagram, shouldn't the magnetic field be going the other way given the direction of current they show? i was just thinking right hand rule.
  • -8 Hide
    johnners2981 , August 31, 2011 4:22 PM
    soo-nah-meeIt's not compound "interest", but it is compounding. If you say something increases 25% each year, you can't just keep adding 25% of the original value! Silly.


    How's it silly? If you're going compound annually then why not compound it monthly, daily, hourly then???
  • 7 Hide
    soo-nah-mee , August 31, 2011 4:47 PM
    johnners2981How's it silly? If you're going compound annually then why not compound it monthly, daily, hourly then???
    You HAVE to compound it at some interval, and since the author said 25% PER YEAR...
  • -6 Hide
    johnners2981 , August 31, 2011 4:55 PM
    soo-nah-meeYou HAVE to compound it at some interval, and since the author said 25% PER YEAR...


    You don't have to compound it, the author also says it doubles in 4 years which obviously involves NO COMPOUNDING
  • 8 Hide
    bobfrys , August 31, 2011 5:04 PM
    Either way the author made a mistake. If you say density increases 25% a year that means 25% larger THAN THE PREVIOUS YEAR.

    If they extrapolated that 25% number from doubling every 4 years then they did their math wrong. It all depends which number is the real number, and which number did they incorrectly pulled out of their ass.
  • 3 Hide
    jamie_1318 , August 31, 2011 5:36 PM
    You have to compound it with the same length as the growth rate is factored in. That's the only way the metrics make sense. It means that each year is 25% more storage than the last year.
  • -2 Hide
    PhoneyVirus , September 1, 2011 1:15 AM
    Getting this for Christmas from the girlfriend I have 18th edition witch was the best version for the FSB X48 last of its kind the good old days, the 19th Edition felt like there was to much information took out. I'm hoping 20th Packs the info about Core 5/7 and some AMD, I found older versions didn't talk about ADM much so again I hope its packed. Looking forward to reading the book this winter well after Christmas then Windows 7 inside out deluxe edition here I come.
  • 0 Hide
    Nnymrod , September 1, 2011 3:00 AM
    Hard drives are really cool, and while SSDs are definitely better in almost every way, and are most definitely the future... I still like hearing platters spin up :)  And they will be the best option for backup drives for awhile.
  • 2 Hide
    Haserath , September 1, 2011 7:36 AM
    asymetriccircleok i dont know all this interest shenanigans, but that first diagram, shouldn't the magnetic field be going the other way given the direction of current they show? i was just thinking right hand rule.

    Actually he is showing the electron flow with the arrows in the first diagram, but the current is the 'positive flow' which is the opposite of the electron flow.
  • 0 Hide
    fstrthnu , September 1, 2011 7:48 AM
    Well Tom's Hardware certainly did their homework here
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