rpt
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Re: How much RAM does the BCM2835 support?

Tue Jan 31, 2012 3:15 pm

Currently the maximum RAM available for the Raspberry Pi is 256M as larger PoP devices are not cost effective. But what is the maximum RAM that the BCM2835 can actually support?

Richard.

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Re: How much RAM does the BCM2835 support?

Tue Jan 31, 2012 3:19 pm

It'll support as much RAM as you like; the problem is sourcing that RAM. 512MB is available in this form factor, but it's really, really expensive at the moment, such that we weren't able to use it and come anywhere near our price point. Moore's Law says that price will come down, and also that more RAM will be packaged like this in the future, so we can hope that in a few years we'll be able to make versions at this sort of price with much more RAM.
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Re: How much RAM does the BCM2835 support?

Tue Jan 31, 2012 3:24 pm

liz said:


It'll support as much RAM as you like; the problem is sourcing that RAM. 512MB is available in this form factor, but it's really, really expensive at the moment, such that we weren't able to use it and come anywhere near our price point.


Can you wave your hands and tell how much more expensive than 256 MB it is? Triple? Five fold? Ten times?

This is some thing us mere mortals wouldn't have a chance to figure out.

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Re: How much RAM does the BCM2835 support?

Tue Jan 31, 2012 3:25 pm

liz said:


It'll support as much RAM as you like


There must be a limit - there are only so many BGA pads on the top of the SoC!

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Re: How much RAM does the BCM2835 support?

Tue Jan 31, 2012 4:09 pm

rpt said:


liz said:


It'll support as much RAM as you like


There must be a limit - there are only so many BGA pads on the top of the SoC!



Ok, ok, not as much as you like. But it is not the balls at the top which are the limit. The maximum memory size supported by the JDEC standard for a 12x12 168 PoP memory is 8Gb (notice small b!). It is always the same problem with making a bigger/different Pi: Logistics. You have to buy different parts, get them produced, keep the batches separated throughout it's complete life cycles which includes selling and shipping.

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Re: How much RAM does the BCM2835 support?

Tue Jan 31, 2012 4:36 pm

Gert said:


Ok, ok, not as much as you like. But it is not the balls at the top which are the limit. The maximum memory size supported by the JDEC standard for a 12x12 168 PoP memory is 8Gb (notice small b!).


So 2G byte is the limit for the PoP. But is this the limit for the SoC? For example, I have used a SoC with an ARM1176 core which limits the physical RAM to 1G byte.


It is always the same problem with making a bigger/different Pi: Logistics. You have to buy different parts, get them produced, keep the batches separated throughout it's complete life cycles which includes selling and shipping.


This isn't the question I asked. I simply want to know what is the theoretical maximum RAM that could be fitted. This could become relevant in a year or two's time when the PoP RAM falls in price and the Pi Mark 2 can use the same SoC but with more RAM for a similar price to today.

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Re: How much RAM does the BCM2835 support?

Tue Jan 31, 2012 4:37 pm

1 GByte

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Re: How much RAM does the BCM2835 support?

Wed Feb 01, 2012 10:36 am

If you are really interested in the PoP memory...

http://www.jedec.org/sites/def.....209-2B.pdf

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Re: How much RAM does the BCM2835 support?

Wed Feb 01, 2012 12:01 pm

walney said:


1 GByte



Yes, but don't forget that in Yorkshire a byte is only 4 bits.  Here in the swanky east of England a byte is 8 bits, and I've heard that in the capital itself a byte is 9 bits and words are 36 bits long.  Now that's posh!

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Re: How much RAM does the BCM2835 support?

Wed Feb 01, 2012 12:04 pm

4bit is a nibble
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Re: How much RAM does the BCM2835 support?

Wed Feb 01, 2012 12:15 pm

rpt said:


Gert said:


Ok, ok, not as much as you like. But it is not the balls at the top which are the limit. The maximum memory size supported by the JDEC standard for a 12x12 168 PoP memory is 8Gb (notice small b!).


So 2G byte is the limit for the PoP. But is this the limit for the SoC? For example, I have used a SoC with an ARM1176 core which limits the physical RAM to 1G byte.


It is always the same problem with making a bigger/different Pi: Logistics. You have to buy different parts, get them produced, keep the batches separated throughout it's complete life cycles which includes selling and shipping.


This isn't the question I asked. I simply want to know what is the theoretical maximum RAM that could be fitted. This could become relevant in a year or two's time when the PoP RAM falls in price and the Pi Mark 2 can use the same SoC but with more RAM for a similar price to today.


In a years time there would be no point in using the same SoC. You will be able to get more powerful devices for the same price.

Checked the datasheet, but cannot find a max ram figure! I seem to remember 1GB from somewhere, could be wrong.
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Re: How much RAM does the BCM2835 support?

Wed Feb 01, 2012 12:46 pm


Checked the datasheet, but cannot find a max ram figure! I seem to remember 1GB from somewhere, could be wrong.


My error, I should have put a bottom line in my post saying: "So that is what we support". So yes: 1Gbyte is the limit.

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Re: How much RAM does the BCM2835 support?

Wed Feb 01, 2012 1:03 pm

According to JamesH "In a years time there would be no point in using the same SoC. You will be able to get more powerful devices for the same price."

Apart from quibbling about Moore's law having 18 months rather than a year, I can well understand that by that time 512 MB (4Gb) RAM will have come down in price to the current 256 MB price, and maybe the 128 MB device will no-longer be produced. So Pi mark X will have 256 / 512 MB for A & B.

But a new SoC? Needing a new board? And a new blob? And all the incompatabilities that would go with that lot? What about the schools - do they throw away all last year's Pis?

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Re: How much RAM does the BCM2835 support?

Wed Feb 01, 2012 1:25 pm

Burngate said:


According to JamesH "In a years time there would be no point in using the same SoC. You will be able to get more powerful devices for the same price."

Apart from quibbling about Moore's law having 18 months rather than a year, I can well understand that by that time 512 MB (4Gb) RAM will have come down in price to the current 256 MB price, and maybe the 128 MB device will no-longer be produced. So Pi mark X will have 256 / 512 MB for A & B.

But a new SoC? Needing a new board? And a new blob? And all the incompatabilities that would go with that lot? What about the schools - do they throw away all last year's Pis?


Much can be done in 256MBytes.

For Herne's sake, we ran WFWG in 2MBytes + 2MBytes expansion.

By the time schools get involved in volume purchasing, perhaps 3-6 months hence, either the larger memory will be available at lower cost or the Pi Foundation will have experience of the educational software currently being worked on and they can, with their partners, provide a recommended set-up for schools.

Calm down dear.

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Re: How much RAM does the BCM2835 support?

Wed Feb 01, 2012 2:02 pm

Burngate said:


According to JamesH "In a years time there would be no point in using the same SoC. You will be able to get more powerful devices for the same price."

Apart from quibbling about Moore's law having 18 months rather than a year, I can well understand that by that time 512 MB (4Gb) RAM will have come down in price to the current 256 MB price, and maybe the 128 MB device will no-longer be produced. So Pi mark X will have 256 / 512 MB for A & B.

But a new SoC? Needing a new board? And a new blob? And all the incompatabilities that would go with that lot? What about the schools - do they throw away all last year's Pis?


Well, there won't be any incompatibilities. Any new SoC in the distant future would use the same standard Linux libraries, would run the same (ish) version of Linux. Any apps written would still work (maybe needing a recompile for best performance).

It's the same with upgraded PC's - software written on one machine works on one with a different processor. Just faster.

Yes, it would need a new board, yes it would need a new blob (probably). Neither of which make any difference to the end user.
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Re: How much RAM does the BCM2835 support?

Wed Feb 01, 2012 2:17 pm

JamesH said:



It's the same with upgraded PC's - software written on one machine works on one with a different processor. Just faster.


But that's just changing the CPU, here we are talking about a new SoC. My experience of Broadcom devices is that when a new SoC comes out, the CPU core is the same as last time but the peripherals have all changed. This involves a complete redesign of both hardware and software.


Yes, it would need a new board, yes it would need a new blob (probably). Neither of which make any difference to the end user.


But it will cost the foundation money and time to redesign. If the same board is used but with bigger memory at the same cost then it is simple. As Burngate suggests we could move to Pi models with 256M/512M instead of 128M/256M.

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Re: How much RAM does the BCM2835 support?

Wed Feb 01, 2012 3:57 pm

Look I use a plug computer (Marvell SOC) at the moment and it took a short while for linux bods to compile everything necessary for debian and a wide suite of core apps and they didnt have manufacturer access to drivers etc  .. Likewise the same with the pi SOC but the pi ppl had the advantage of Broadcom links

and if you want further proof of how quickly these unix guys can get a unix distro up and running on different SOC's you only need look to the chinese android TV settop box (on several different SOC's) or tablet marketplace where in a matter of weeks after google releasing Android ICS these very small (almost one man band) set top box makers have ICS running pretty much perfectly  ... and all say within a month of google releasing the google TV source code they will have it up and running on their boxes.

It may be that some changes need to be made for custom GPU or low level interfacing code but you can't get that low level with the broadcom GPU anyway (as its closed) and i'm sure the discount beagleboarders will have no problem changing a few addresses in their code.

You have to look forward or you die  .. so its good that already the pi ppl are looking to the pi2  .. hopefully by then they will have a bit of cash and preorder volume (MOQ) to go for a more punchy SOC  and a good bit of RAM in the pi2  ... most of the community infrastructure should move across seamlessly multiple produts (SOC's) and i'm sure the pi's I/O interfaces are generic enough to survive the transition intact bar a few address changes

roll on pi2 with a different SOC

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Re: How much RAM does the BCM2835 support?

Wed Feb 01, 2012 4:06 pm

rpt said:


JamesH said:



It's the same with upgraded PC's - software written on one machine works on one with a different processor. Just faster.


But that's just changing the CPU, here we are talking about a new SoC. My experience of Broadcom devices is that when a new SoC comes out, the CPU core is the same as last time but the peripherals have all changed. This involves a complete redesign of both hardware and software.


Yes, it would need a new board, yes it would need a new blob (probably). Neither of which make any difference to the end user.


But it will cost the foundation money and time to redesign. If the same board is used but with bigger memory at the same cost then it is simple. As Burngate suggests we could move to Pi models with 256M/512M instead of 128M/256M.


Believe me, it's not a problem. Broadcom have faster SoC's running Linux (and ICS), if Raspi chose to use one of those it would just be a board redesign - the software would already be in place.

Although just increasing the memory would also be an option if that physical particular size drops in price enough.
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Re: How much RAM does the BCM2835 support?

Wed Feb 01, 2012 4:38 pm

JamesH said:




It's the same with upgraded PC's - software written on one machine works on one with a different processor. Just faster.



Yes, it would need a new board, yes it would need a new blob (probably). Neither of which make any difference to the end user.



Believe me, it's not a problem. Broadcom have faster SoC's running Linux (and ICS), if Raspi chose to use one of those it would just be a board redesign - the software would already be in place.

Although just increasing the memory would also be an option if that physical particular size drops in price enough.



Thanx, James. I don't care about how much memory there is - 128 is way greater than what I've been used to. So forcing me to have more is not a problem!

Just so long as we get a good run at this pi before we find it's out of date!

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Re: How much RAM does the BCM2835 support?

Wed Feb 01, 2012 4:59 pm

Burngate said:


JamesH said:




It's the same with upgraded PC's - software written on one machine works on one with a different processor. Just faster.



Yes, it would need a new board, yes it would need a new blob (probably). Neither of which make any difference to the end user.



Believe me, it's not a problem. Broadcom have faster SoC's running Linux (and ICS), if Raspi chose to use one of those it would just be a board redesign - the software would already be in place.

Although just increasing the memory would also be an option if that physical particular size drops in price enough.


Thanx, James. I don't care about how much memory there is - 128 is way greater than what I've been used to. So forcing me to have more is not a problem!

Just so long as we get a good run at this pi before we find it's out of date!


I don't think going out of date is an issue, if in the fullness of time a faster device is built, the old ones still work, and if they were fast enough for what you wanted to do with them, they are still fast enough!
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Re: How much RAM does the BCM2835 support?

Wed Feb 01, 2012 5:09 pm

Burngate said:


Just so long as we get a good run at this pi before we find it's out of date!



Heard the saying: if it it's in stock it is out of date!

Going back to the memory chip itself the beta boards have a Hynix h9tknnn2gdmplr

Change the 2 for a 4 and you get the 512MB part!

I thought I'd keep a track on the trade price over the next few months, but I've not been able to find a distributor stocking them:-( I did spot that the 512MB part are 'Samples only' so not surprising they are to expensive for the Pi

and I couldn't find any equivalents (pity it's not standard numbering like 4256z-80!

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Re: How much RAM does the BCM2835 support?

Wed Feb 01, 2012 5:14 pm

arm2 said:


Burngate said:


Just so long as we get a good run at this pi before we find it"s out of date!


Heard the saying: if it it"s in stock it is out of date!

Going back to the memory chip itself the beta boards have a Hynix h9tknnn2gdmplr

Change the 2 for a 4 and you get the 512MB part!

I thought I"d keep a track on the trade price over the next few months, but I"ve not been able to find a distributor stocking them:-( I did spot that the 512MB part are "Samples only" so not surprising they are to expensive for the Pi

and I couldn"t find any equivalents (pity it"s not standard numbering like 4256z-80!


Micron already list the 1GByte device as in production.

It's all about price and need.

256MBytes is a good size for many if not most applications.  OK you may have trouble holding multiple tasks in memory.  But then it's aimed at teaching programming.  So right now I believe 256MBytes will fit many, if not most, users.

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