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In the market, you can get USB drives of different storage sizes. However, among the same brand, I found that those USB drives are physically the same.

How can they achieve this? Is it that different USB storage sizes make use of different file systems?

If they are using the same storage technology, wouldn't their production cost actually be the same for 8 GB and 16 GB USB drives – since they have the same physical size?

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closed as not constructive by techie007, Linker3000, Breakthrough, Nifle, Wuffers Aug 29 '11 at 23:55

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You are equating "physically the same" with having "the same physical size". Two things that are the same size do not have to be physically the same! –  David Schwartz Aug 25 '11 at 21:37
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Size matters not! Judge me by my size do you? –  surfasb Aug 26 '11 at 2:59
    
@Kit Ho: consider two people of the same size. one goes to the gym and does heavy lifting, while the other doesn't do any exercise. Which out of the two do you think will be more powerful? It's the same with 8GB and 16GB. Though they look the same, the 16GB is packed with more chips or a single more chip. Get it?? :D –  user95609 Aug 26 '11 at 7:59
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To quote Ron Gilbert on Twitter: “First hard drive I ever saw was 5MB and measured 3ft x 2ft. I just lost 8GB of storage in my couch cushions.” – Physical size does not mean anything :) –  poke Aug 26 '11 at 10:32
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Want to really blow your mind? Sometimes different sized drives will have the same storage chips internally, but the smaller drive had a failure when tested at full capacity, so it was retested at the lower size and passed. This used to be much more common than it is today however. –  Jim McKeeth Aug 26 '11 at 21:04
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5 Answers

up vote 46 down vote accepted

The density of the storage is higher. Put simply there are more NAND flash memory chips (or the chips can hold more). The chips are very small though, so there is some empty room in most USB sticks. Making the chip bigger, or adding a second is almost always possible in the same space.

To save space, NAND flash chips also often package two pieces of silicon to same "chip", meaning the plastic/ceramic piece you usually call "chip" has one, two or four individual pieces of silicon inside. This comes with performance cost, but on USB stocks performance is not usually a concern. This all is made possible by transistors used to implement the memories shrinking all the time.

If you think about microSD cards, they are smaller than nail on my index finger, and they still come with capacities of 16 GB or more. Or SD cards, size of a stamp and 2 mm thin, come in capacities of 128 GB... And one SD card is easily smaller in physical volume than most USB sticks.

It is also a common practice in electronics design to first create the top-end model with all bells and whistles and then just not install some components to get the cheaper models; so these two sticks might very well be all identical, except one of them, while having space for another 8 GB die, does not come with it installed.

The reason for this is that designing the circuit board, testing the design, making molds for plastic parts, etc. is the expensive part. Making a single unit is cheap compared to that. Which means it makes sense to keep the plastic cover and circuit board identical, and just leave out some components, because you then save on the expensive part, materials.

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To expand on @soandos' answer, you can't think of storage expressly in physical volume. It is not the same as having a storage tub that you stuff things in. It is similar to why you can have two RAM sticks that are the same size, but one is 2GB and one is 4GB. The 4GB one just has more chips on it. The cost of production will still be higher for the larger drive if for nothing more than the additional number of parts, but there is the added development cost in the initial design process as well. –  MaQleod Aug 25 '11 at 18:51
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This is no different from hard drives all being the same form factor but vastly different sizes, if that helps you wrap your head around it. –  Shinrai Aug 25 '11 at 18:52
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A better example is a CD, DVD, and BluRay. They look exactly the same, but hold vastly different amount of storage. –  Keltari Aug 25 '11 at 19:04
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An even better example is a $1 bill, a $20 and $100, they look pretty much the same, have the same physical size but hold a vastly different amount of cash ... ;-) –  jlliagre Aug 25 '11 at 21:29
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@Kit-Ho - I think you are confusing technologies here. File systems have nothing to do with the storage capacity of the USB drives. If you were to pry off the plastic cases of the 8 and 16GB USB drives you would see 2 flash memory chips. Those chips are the 8 and 16GB storage containers that hold all your data. Those chips are manufactured differently and thats the reason why they are different sizes and cost different. The larger capacity something is, the harder it is to cram into such a small space. –  Keltari Aug 26 '11 at 4:47
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What gives the capacity of the USB drive is the amount of memory it has inside. The NAND memory is stored inside some chips. If you open your USB drive, you can see the chip inside it. Here's a NAND chip:

enter image description here

Even chips of the same size can have a different amount of memory space inside it. So, just the physical size of the chip isn't a indicative of it's capacity.

As you can imagine, chips with more memory have to be built in a different way: more raw material, different layouts, different amounts of eletronic components. So, bigger ones will cost more.

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The size of the USB stick is determined by the marketing people, the design department, and not necessarily the components inside it.

There are USB memory sticks that hold gigabytes of data that fit completely inside the USB port they are plugged into.

For a good example of just how small a thing large amounts of data can fit into, look at Micro-SD cards, which are used in many cell phones. The package is less than a centimeter on a side, only a mm or so thick, and can hold up to 32GB of data.

Generally, higher density components are more expensive. So a normal size USB memory stick doesn't have to use the most expensive, most dense components.

USB sticks are generally designed to fit comfortably within the hand and pocket. Smaller devices are more prone to getting lost, and larger devices won't fit in the pocket quite as well.

So in designing these devices, the company decides on a price point, which will govern to a certain extent how expensive the components can be, the design department decides on a branding and design and size, and then the technical people are told to make it work.

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+1 for "the technical people are told to make it work". –  MrMisterMan Aug 26 '11 at 8:09
    
And, just like magic, we always do. :) –  music2myear Aug 26 '11 at 14:10
    
@Peter Mortensen I appreciate your concern about such small syntax issues in my answer. However, please leave my posts as-is unless there are glaring and significant issues. Thank you. –  music2myear Aug 29 '11 at 22:20
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Inside the drive casing, there's a circuit board with some logic chips and some memory chips on it. It's likely that either:

  • The 8 GB uses the same board but leaves off half the chips that the 16 GB has installed
  • The 8 GB uses a different memory chip with half the capacity, but a similar package (and inside that package, there's half as much actual circuitry, as soandos suggests)

A large fraction of the part cost for a USB drive is probably in the memory chip. All other things being equal, a 16 GB chip should cost slightly more than 2 8 GB chips (because compactness is worth something), so it's not completely out of line to double the price when you double the capacity (especially at the high end of capacity, where the chip is a bigger part of the cost). Looking at one brand of USB drive with identical form factors, I'm seeing 4 GB for $15, 8 GB for $25, 16 GB for $40, 32 GB for $70 which is less than doubling at each step.

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Manufacturers would save money if they can just use the same casing for all the size options and then just fill it with what is needed the out side of the case does not determine size of the storage. mainly because it is not practical to do it that way.

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