Does RAM not wear out from read/write cycles like flash memory?

[Filingo]

It seems like RAM is being written/read non-stop yet it doesn't seem to have its memory go bad.

How does it work?

[Eigenvektor]

It's different technology. RAM is not permanent storage like an SSD. When the power goes out it loses its contents and it actually needs to be periodically refreshed. It's made out of a ton of tiny capacitors, so it has no longevity issues.

[WereCatf]

1 minute ago, Filingo said:

Does RAM not wear out from read/write cycles like flash memory?

No, it doesn't. RAM loses its contents as soon as power goes out, but flash - memory has to retain its contents for a long time without any power, and so they're electrically nothing alike.

[amckern]

ELI5:

 

Random Access Memory is a volatile memory - it has no ability to store data

 

The memory on a SSD is non-volatile, it holds the data in a statically charged status - when the drive starts to ware out its because the cell is either week & cannot hold a new charge (think of it like the battery on dads old iPhone), or the cell can not discharge the existing charge

Edited May 4, 2021 by amckern
Spelling (dont use google search for spell check)

[Filingo]

Just now, Eigenvektor said:

It's different technology. RAM is not permanent storage like an SSD. When the power goes out it loses its contents and it actually needs to be periodically refreshed. It's a capacitor, so it has no longevity issues.

I thought that the memory itself is flash like storage device but it just goes off. You're saying that it's not the same flash material that storage is made of? 

[Eigenvektor]

6 minutes ago, Filingo said:

I thought that the memory itself is flash like storage device but it just goes off. You're saying that it's not the same flash material that storage is made of? 

No, RAM is made from capacitors (and transistors), so it can keep an electrical charge only for a limited amount of time. It is not permanent like flash storage. As  I said it even needs to be periodically refreshed, otherwise it would lose its contents even while your PC is turned on.

 

RAM is also a lot faster than SSD storage, so no they are not the same at all.

[Filingo]

Thank you guys

[Doug_Dangger]

This never took off.

[mariushm]

(not really technically correct, super simplified, but good enough)

 

You can think of ram  as millions of   pairs of super tiny incandescent bulbs each glued to a calculator solar cell - the solar cell outputs some voltage if there's light produced by the incadescent bulb , or nothing if it's dark.

 

If you want to set a bit to 1, the ram chip sends a pulse of energy into the incadescent bulb - the filament heats up and produces light... but as soon as there's no more pulse of energy,  the filament starts to cool down and brightness decreases.

There's a circuitry in the ram chips which constantly checks if any solar cell outputs some voltage, and if so, another pulse is sent to that particular incandescent bulb making it bright again - the trick is checking and sending pulses faster than the cool down time, you don't want the bulb's brightness to go below some threshold where you're no longer sure the bulb is 1 or 0.

If you want to set a bit to 0, the circuitry that keeps checking and sending pulses to refresh the incadescent bulbs is instructed to skip sending pulse to that particular bit. 

 

So you can replace the incadescent bulb with a capacitor, a component which holds a charge, but is slowly leaking that energy (losing it) and a transistor which can detect if that capacitor holds a charge. 

So it's a super simple circuit, one capacitor and one transistor, repeated billions of time inside a silicon die, then you have the circuitry which periodically checks each bit and refreshes it. 

 

Because the capacitors are designed to be simple and to leak, data is lost within seconds of disconnecting power.

 

SSDs are designed a bit differently, and there's more components involved in holding bits inside the chips. 

A more complicated component is used, which holds the charge for long time .. so it's no longer working like an incandescent bulb always having to be refreshed because the light fades out, but the component is much slower and takes more time for the energy amount to be set just right inside a bit cell, and it also requires a more complex circuit to discharge the cell, to reset it back to 0.

It's not the writing to flash memory that causes the wear, it's the erasing circuit which gradually wears out the memory cells... after a number of erases, the cells can no longer reliably hold the charge at a precise enough level for the ssd controller to easily say "that's a 0 , that's a 1  , this 2 bit cell holds bit 0 set to 1 and bit 1 set to 0 " and so on... 

 

 

 

[Filingo]

45 minutes ago, mariushm said:

(not really technically correct, super simplified, but good enough)

 

You can think of ram  as millions of   pairs of super tiny incandescent bulbs each glued to a calculator solar cell - the solar cell outputs some voltage if there's light produced by the incadescent bulb , or nothing if it's dark.

 

If you want to set a bit to 1, the ram chip sends a pulse of energy into the incadescent bulb - the filament heats up and produces light... but as soon as there's no more pulse of energy,  the filament starts to cool down and brightness decreases.

There's a circuitry in the ram chips which constantly checks if any solar cell outputs some voltage, and if so, another pulse is sent to that particular incandescent bulb making it bright again - the trick is checking and sending pulses faster than the cool down time, you don't want the bulb's brightness to go below some threshold where you're no longer sure the bulb is 1 or 0.

If you want to set a bit to 0, the circuitry that keeps checking and sending pulses to refresh the incadescent bulbs is instructed to skip sending pulse to that particular bit. 

 

So you can replace the incadescent bulb with a capacitor, a component which holds a charge, but is slowly leaking that energy (losing it) and a transistor which can detect if that capacitor holds a charge. 

So it's a super simple circuit, one capacitor and one transistor, repeated billions of time inside a silicon die, then you have the circuitry which periodically checks each bit and refreshes it. 

 

Because the capacitors are designed to be simple and to leak, data is lost within seconds of disconnecting power.

 

SSDs are designed a bit differently, and there's more components involved in holding bits inside the chips. 

A more complicated component is used, which holds the charge for long time .. so it's no longer working like an incandescent bulb always having to be refreshed because the light fades out, but the component is much slower and takes more time for the energy amount to be set just right inside a bit cell, and it also requires a more complex circuit to discharge the cell, to reset it back to 0.

It's not the writing to flash memory that causes the wear, it's the erasing circuit which gradually wears out the memory cells... after a number of erases, the cells can no longer reliably hold the charge at a precise enough level for the ssd controller to easily say "that's a 0 , that's a 1  , this 2 bit cell holds bit 0 set to 1 and bit 1 set to 0 " and so on... 

 

 

 

awesome, that's the type of explanation I needed since I'm not an electrical engineer

 

  

1 hour ago, Doug_Dangger said:

This never took off.

 

haha nice, I think Linus did a video on one of these?

[Beerzerker]

Seriously - You'd be suprised how many would be willing to pay a few bucks for one of those.

[Mark Kaine]

9 hours ago, Eigenvektor said:

No, RAM is made from capacitors

but caps dont last forever, 20 - 30 yrs maybe on average?

 

[Eigenvektor]

19 minutes ago, Mark Kaine said:

but caps dont last forever, 20 - 30 yrs maybe on average?

True, but that would be based on deterioration of the materials used in the capacitor and has less to do with its number of "write cycles". It's also a lot longer than you typically keep RAM sticks around, so it's not something most users need to worry about. An SSD on the other hand has a limited number of write cycles, because flash cells slowly deteriorate each time you change their state.

[mariushm]

27 minutes ago, Mark Kaine said:

but caps dont last forever, 20 - 30 yrs maybe on average?

 

We're talking about extremely small capacitors which only have to hold an extremely small charge of electricity.

 

The capacitors you're thinking of, the big round things you see on motherboards and video cards are capacitors designed with other materials and chemical substances and they're meant to store really big amounts of energy.

As a comparison, let's say a regular electrolytic capacitor has a capacitance of 1000 uF ... those very tiny ceramic capacitors under the cpu or gpu chip are usually 10 or 100 nF, which is 0.01uF  or 1 / 100 of 1 uF  ... so not 1000 times smaller, but 100k times smaller.

And those tiny 0402 ceramic capacitors are still HUGE compared to what's inside a ram chip ... a 1 GB chip has at least 1024  (megabytes) x 1024 (kilobytes) x 1024 (bytes)  x 8 capacitors (1 per bit) ... so billions of capacitors in around 1 finger tip.. they're very small and hold very little charge.

Even if they degrade a bit over time, we're talking about capacitors that only need to properly store a 0 or 1, two states... so if that capacitor degrades by 10-30% in 20 years, it will still reliably store a strong enough charge to be detected as 1.

 

The electrolytic capacitors are designed to meet some requirements, like how fast can they charge up, how fast can they give the charge to components and so on... they degrade if those parameters are exceeded, or if subjected to significant heat, and other reasons... in the end most electrolytic capacitors are only rated for 25-30 years because that's how long the rubber or whatever material is used to seal the bottom of the capacitor.. as humidity and temperature variations affect the plastic/rubber/material, it can developer microscopic cracks/holes/imperfections and then the actual liquid or semi liquid chemicals inside can leak or can dry out, and then capacitors degrade.

 

As an idea, here's a picture of a 1 mebibyte chip - that's 1²⁰ or 1,048,576 bits or 128 KB -  used in the 285/386 days. They put 8 such chips on a stick to a  1 MB  ram stick:

You can get a higher quality picture here : https://zeptobars.com/en/read/Micron-MT4C1024-dram

 

So keep in mind this whole chip is 8 mm by 4 mm (8662x3969µm)  the die sits in the middle of a rectangle chip and bonding wires are used to connect the die to the pins

 

 

example of a silicon die and bonding wires connecting the die directly to a circuit board