Why are storages powers of 2?

[bizack]

So, why SSDs have no problem with wasted address bits (as in 20-chip example above)?

Those are separate NANDs (with stacked dies in each NAND). Also:

"The total flash capacity is actually 320 Gbytes, so a high level of overprovisioning was implemented."

So you're buying a 320GB SSD, but only getting 200GB. If you're a manufacturer, it becomes cost effective to produce the same boards, but artificially cap the addressable space and sell SSDs at different price-points, even though they're physically the same.

You're also dealing with consumer mindset:

16GB, 64GB or 128GB

As a consumer, I can see that 64 is 16x4 and I can see that 128 is 64x2. I internalize that as four times as much, and twice as much. When you start working with non-multiples, it's a harder sell.

 

[samiznaetekto]

The 6 and 6+ have a single flash memory chip installed in them, so whatever capacities that those chips are manufacturered is what Apple can use.

So, it's one die, not several stacked ones like in Samsung link above? What makes you think so?

 

[T5BRICK]

So, it's one die, not several stacked ones like in Samsung link above? What makes you think so?

It doesn't matter if it's a single die or several stacked ones, Apple is using an off the shelf component so the 16/32/64/128GB capacities are all you're going to get.

*edit* and if you're curious as to why I think it's a single memory chip... https://www.ifixit.com/Teardown/iPhone+6+Teardown/29213

 

[samiznaetekto]

Those are separate NANDs (with stacked dies in each NAND). Also:

"The total flash capacity is actually 320 Gbytes, so a high level of overprovisioning was implemented."

So you're buying a 320GB SSD, but only getting 200GB.

Yes, that's what I said. Neither 200 nor 320 are powers of 2. Power of 2 only has its magic when applied to a single, indivisible chip. But you can include 20, 15, 17, 77 - any number of them in the product. So, while the overprovisioned space (320) is divisible by a power of 2 (16), it's not a power of 2 by itself.

As a consumer, I can see that 64 is 16x4 and I can see that 128 is 64x2. I internalize that as four times as much, and twice as much. When you start working with non-multiples, it's a harder sell.

Well, there's no problem selling SSDs and hard drives in non 2^N capacities. I don't think most consumers think in powers of 2. They think how much stuff do I need to store? If the user is starting to feel tight with 16GB, they might think, "I just need 5 gigs more, and I'll be fine". So, if there was a 24GB iPhone, they'll buy that. These steps in power of 2 are simply forced by manufacturers. If your pants feel a bit tight, you don't by the 2x or 4x larger ones, now do you?

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It doesn't matter if it's a single die or several stacked ones, Apple is using an off the shelf component so the 16/32/64/128GB capacities are all you're going to get.

*edit* and if you're curious as to why I think it's a single memory chip... https://www.ifixit.com/Teardown/iPhone+6+Teardown/29213

I actually checked this teardown before starting the thread. Yes, this chip is a single package, but of how many stacked dies?

 

[bizack]

Yes, that's what I said. Neither 200 nor 320 are powers of 2. Power of 2 only has its magic when applied to a single, indivisible chip. But you can include 20, 15, 17, 77 - any number of them in the product. So, while the overprovisioned space (320) is divisible by a power of 2 (16), it's not a power of 2 by itself.



Well, there's no problem selling SSDs and hard drives in non 2^N capacities. I don't think most consumers think in powers of 2. They think how much stuff do I need to store? If the user is starting to feel tight with 16GB, they might think, "I just need 5 gigs more, and I'll be fine". So, if there was a 24GB iPhone, they'll buy that. These steps in power of 2 are simply forced by manufacturers. If your pants feel a bit tight, you don't by the 2x or 4x larger ones, now do you?

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I actually checked this teardown before starting the thread. Yes, this chip is a single package, but of how many stacked dies?

My last comment will be that a) it's good that you're curious and obviously intrigued by this subject and b) the answer isn't always a technical one.

Say you're the head of product for iPhone. You have a meeting with Tim Cook about iPhone 6. He asks 'so what configurations are we offering this year?' You respond '15GB, 60GB and 115GB.' His response probably won't be 'oh, cool, so we're going to offer non-standard sizes that conflict with the rest of the industry and will very likely confuse our users.' Additionally 'and we'll have to cut new deals with our manufacturers which will probably increase overall cost since yields for these configurations aren't as large.' Great job!

People don't think in powers of 2, but my example was multiples of 2 (64 is 16x4 and 128 is 64x2... the Apple employee at the Apple store can easily explain that this model is 4x as much as this model and this model is 2x as much as this model). It's easy to explain, understand, and put a price tag on.

 

[T5BRICK]

I actually checked this teardown before starting the thread. Yes, this chip is a single package, but of how many stacked dies?

Like I said, it doesn't matter how many stacked dies there are. Apple is limited to the sizes available from the chip manufacturer.

 

[samiznaetekto]

Like I said, it doesn't matter how many stacked dies there are. Apple is limited to the sizes available from the chip manufacturer.

If having 3 16GB dies on a chip is physically possible and Apple wanted to have 48GB capacity, don't you think Apple would just tell the manufacturer what they want?

Again and again, what's the principal difference between SSD drives and flash memory in smartphones? Why one can be in non-2^N sizes, and the other is only in 2^N sizes? Apparently, customers are OK with having non-2^N sizes on laptops and desktops. What makes you think they won't be OK with having non-2^N sizes on smartphones?

 

[cd3267]

I'm assuming they're in powers of 2 due to binary conversions.

 

[samiznaetekto]

Say you're the head of product for iPhone. You have a meeting with Tim Cook about iPhone 6. He asks 'so what configurations are we offering this year?' You respond '15GB, 60GB and 115GB.' His response probably won't be 'oh, cool, so we're going to offer non-standard sizes that conflict with the rest of the industry and will very likely confuse our users.' Additionally 'and we'll have to cut new deals with our manufacturers which will probably increase overall cost since yields for these configurations aren't as large.' Great job!

iPod (classic) had capacities like 5, 10, 15, 20, 30, 40, 60, 80, 120, 160:

http://www.everymac.com/systems/apple/ipod/index-ipod-specs.html

Yes, it was a spinning drive, so it can be made in almost arbitrary size, so why not 2^N sizes? And Apple wouldn't be here if those "non-standard" sizes didn't sell like hotcakes.

 

[gr8tfly]

iPod (classic) had capacities like 5, 10, 15, 20, 30, 40, 60, 80, 120, 160:

http://www.everymac.com/systems/apple/ipod/index-ipod-specs.html

Yes, it was a spinning drive, so it can be made in almost arbitrary size, so why not 2^N sizes? And Apple wouldn't be here if those "non-standard" sizes didn't sell like hotcakes.

First, because a spinning disk is not built out of binary circuits (see previous pages of this thread). Second, Apple would have had to go with what the industry was supplying, which was very limited in the 1.8" form factor. Something called economy of scale...which also applies to solid-state devices. Apple isn't in the business of building storage devices – rotational or solid-state.

 

[T5BRICK]

If having 3 16GB dies on a chip is physically possible and Apple wanted to have 48GB capacity, don't you think Apple would just tell the manufacturer what they want?

I'm sure Apple could, but you do realize that a custom capacity would cost more per GB than a standard capacity, right?

Again and again, what's the principal difference between SSD drives and flash memory in smartphones? Why one can be in non-2^N sizes, and the other is only in 2^N sizes? Apparently, customers are OK with having non-2^N sizes on laptops and desktops. What makes you think they won't be OK with having non-2^N sizes on smartphones?

A SSD has an array of memory chips of standard capacity while a smart phone typically only has a single memory chip for storage. We're going to ignore stacked dies because they don't matter.

 

[andyblila]

Why is it that it's always 16GB, 32, 64, 128 for phone storage and such? Why not, say, 20, 30, 50, 75?

The amount of data you need to store does not grow exponentially with time, more like linearly. And in real life, we don't double each step and don't buy things in powers of 2. Is 10-pound bag of potatoes too small for you? Buy 15.

So, why?

The binary system.

 

[PegasusTenma]

This is the nerdiest thread ever.

 

[Rigby]

If having 3 16GB dies on a chip is physically possible and Apple wanted to have 48GB capacity, don't you think Apple would just tell the manufacturer what they want?

Why would Apple want to use an expensive custom chip rather than cheap off-the-shelf versions?

Again and again, what's the principal difference between SSD drives and flash memory in smartphones?

As was mentioned "again and again", SSDs usually use multiple chips, phones usually do not. For the same reason SD cards and compact USB flash drives come only in powers of 2.