Overclockers Australia - Anatomy of an IBM Deskstar 75GXP hard drive

Anatomy of an IBM Deskstar 75GXP hard drive
24-April-02 - Article by Manaz

All images on this page are clickable..

I think it's fairly safe to say that, without exception, everyone reading this article has at least one hard drive in their PC. Hard drives, whilst they were initially only an (expensive) option when PCs were first introduced to the world, have now become indispensible. Modern day operating systems are getting bigger by the generation, applications take up more space with each update, and some operating systems and applications have become so memory hungry that not only do PCs use the RAM that is physically installed in them, but also hard drive space as "virtual" memory. Six years ago, I bought a brand new system with a massive (for the time) 2GB hard drive in it. Six weeks ago, I bought a 60GB hard drive to replace the recently failed 20GB hard drive (the IBM drive in the title of this article) - and that 60GB hard drive is nowhere near the biggest which is readily available - Western Digital have a 100GB version of the same drive I bought, and IBM's latest 120GXP series of drives tops out at 120GB. And that's just IDE drives. SCSI drives are often bigger and faster than their IDE counterparts, though they carry a premium price over IDE drives for various reasons (which are beyond the scope of this article).

As I mentioned before, my 20GB IBM 75GXP recently decided to (unsurprisingly, thanks to the bad reputation IBM 75GXP hard drives seem to have earned themselves) die. The usual symptoms (for the death of a Deskstar) occurred - the drive became slow and noisy - the noise graduating from a dull whine to a grinding sound, as my data became more and more often corrupted, until eventually, about six weeks ago, Windows refused to boot. I've since replaced the IBM drive with a 60GB Western Digital, and the 20GB has kicked around my desk for a while, as I've been too busy to really sit and figure out what I was going to do with it.

In the end, I decided that it wasn't worth the effort of obtaining an RMA and posting the drive to IBM in Singapore, just to get another 20GB drive with a dubious reputation back - especially since the drive was no longer really needed, as I had replaced it. The drive kicked around my desk for a bit longer - I tend to hold on to "useless" computer parts for some reason, until I hit on an idea - since I've recently bought myself a Nikon Coolpix 995 digital camera, I thought I'd put together a bit of a photo essay, showing the inner workings of a modern hard drive.

Before I go on, I should make the following VERY clear to you. Opening your hard drive (or even just loosening and tightening a single one of the screws in it) WILL invalidate any warranty you have on your drive. Hard drives are manufactured in "clean" conditions - with no dust. Opening a hard drive will invariably lead to dust settling inside it - which will more than likely cause problems should you try to put the drive back together and use it again. As you will see later, even touching the platters inside the hard drive leaves marks on it - marks which can cause data loss or corruption, not to mention drive head crashes. Do NOT do anything like what I did with this drive unless you are 150% sure that you don't need the drive ever again, and that nothing on it is of ANY value to you at all. If you're crazy enough to pull a drive apart, put it back together and try to operate it again, neither I nor Overclockers Australia accepts ANY responsibility for any problems you may have with the drive, or the rest of your system, after doing so. You've been warned...

Here you have my IBM Deskstar 75GXP hard drive (on the right). Next to it, just for comparison, is an old 2GB Fujitsu SCSI-1 hard drive - made in 1994, it's a double height, 5.25" device (approximately 210mm x 150mm x 85mm) - and it weighs around 3.2kgs. The IBM drive, on the other hand, was made in 2001, is approximately 145mm x 100mm x 25mm, and weighs 570g. For that reduction in size, 7 years of development allows the IBM to hold 10x the data of the Fujitsu. I was planning on taking the Fujitsu drive apart as well, but unfortunately, quite a few of the screws holding it together have had their heads reamed, and so I can't get a screwdriver to take them out.

Here I have started to remove the screws holding the top plate of the drive in place. The six screws from around the edges have been removed. The remaining four screws had plastic covers over them - evidently designed to stop people doing the sort of thing I was about to do. Two of the remaining four screws were also completely covered by the label on top of the drive - a craft knife took care of both the label and the plastic covers - you can see the holes cut in the label quite clearly, but the plastic covering the screws was clear, so it's a lot harder to see.

Most hard drives don't use regular philips head or flat head screws - they use torx head screws. Torx drivers are required to undo these - you cannot use a regular screwdriver to loosen or tighten these screws. I don't know of any technical reason why torx head screws are better than philips or flat head - other perhaps than the fact that torx drivers aren't widely available, so using torx head screws may help stop people playing around when they shouldn't. Unfortunately for this drive, I've got access to torx drivers.

This picture shows two things. One - IBM don't always line the sticker on top of the drive up to where it's supposed to go. Two - this drive (just like all modern drives) has a hole in it. Contrary to popular belief, hard drives aren't actually sealed. This would be silly, for at least one very good reason. As the drive starts up, the platters spin up - in the case of this IBM 75GXP, the platters are spun up to a speed of 7,200rpm. Spin ANYTHING at 7,200rpm, and it's going to heat up, due to friction caused by the air surrounding it moving across the surface. And it's not just the surface of the spinning object (in this case, the set of drive platters) that heats up - the air will heat up as well. As air heats up, it expands. Expanding air inside a sealed enclosure will increase the air pressure inside that enclosure - leading to stress being put on the enclosure, as the air pressure inside tries to equalise with the air pressure outside. A hard drive which starts to warp out of shape is a bad idea - hence the hole - it allows the air to flow out of the drive as it heats up, so that no pressure builds up inside - and it lets air flow back into the drive as it cools - keeping the air pressure inside and outside even.

With all the screws removed from the top of the drive, the top cover came off surprisingly easily. Some manufacturers use a sticky foam-type substance to seal the top cover onto the drive - IBM have used a thin line of something that seems a little like silicon sealant to seal the drive. It's well and truly stuck to the top cover - but it's not sticky where it makes contact with the bottom part of the drive. A few things are immediately obvious when the drive is opened. The platters are the most obvious thing you can see - they're big (compared to the rest of the components), round and very shiny. In the centre of the platters is the motor which turns the platters - the bearings in the motor are VERY high quality, as the platters have to rotate VERY evenly. Running along the side of the platters are the actuator arms for the drive heads - they are controlled by the silver device in the bottom left corner of the drive (which consists of two VERY strong permanent magnets and a carefully produced wire coil on the end of the actuator arms). The orange plastic in the bottom right of the drive casing covers the wires that lead from the drive electronics (which are on a PCB underneath the drive casing). On the bottom surface of the top cover, you can see the line of sealant I mentioned before, and something attached underneath the hole I mentioned earlier.

This is the said "something". I mentioned before that the hole on top of the drive cover was to let air move in and out of the drive as it changes temperature - this is a filter, to ensure that any air which does come into the drive is clean. To give you an idea as to the size of it, it's about 9mm in diameter, and 4mm high.

I'm not sure if all hard drives these days have this feature. The little white plastic bits attached to the side of the drive casing are a "safe" area for the drive to leave the drive heads when it's shut down. There's no chance that the heads will be forced into the platters (causing considerable damage and data loss) by a sudden movement - such as the drive being bumped. *Really* old PCs (like the NEC 80286 based PC my family owned back in 1988) had a "park" command - which told the hard drive to move the heads into such an area. Obviously the IBM drive does this automatically when it's shut down (the heads were parked there when I opened the drive).

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