How much RAM does an embedded computer really need?

[technix]

So it is that question again, how much RAM do you need for an embedded computer, especially for debugging and testing purposes?

For example, is it overkill to set up 256MB SDRAM on AT91SAM9260 maxing it out?

[Siwastaja]

Obviously, it's about the use case, most suitable tool for the job. Simple jobs have not gone anywhere.

For simple control which does not involve storing images, audio, large datasets, whatever, just some classic control, 1KB microcontroller does; or if I want an actual computer which runs linux, gnu tools and TCP/IP stack and whatever making my life easy, then maybe 128MB does (mostly for OS overhead!), this would be an embedded router / openwrt territory. If I want to connect it to a process control / infotainment monitor, then I might want HDMI and maybe 1GB of memory allowing a web browser; this would be Raspberry3 territory.

[DiTBho]

So it is that question again, how much RAM do you need for an embedded computer, especially for debugging and testing purposes?

I am fine with the first Fon-v1, which only has 16Mbyte of ram but it's ok for what I do with the board, whereas I am in big troubles with my JN1 because 512MB are not sufficient for what I'd like to do with that board.

So I don't know .... maybe the answer depends on what you want to do? 

[DiTBho]

computer which runs linux, gnu tools and TCP/IP stack and whatever making my life easy, then maybe 128MB does (mostly for OS overhead!)

The fon-v1 has 16MB of physical ram. It can be somehow hacked to have 32MB, you have do desolder the chip, solder a bigger one, modify the firmware, and pray.

I will do it ... sooner or later, in the meantime it still has 16MB, and it's loaded with:
- kernel 2.6.26 stripped: 5Mbyte < ----- I am afraid you cannot achieve this with kernel v3, v4, v5
- digest libC stripped: 2Mbyte  <----- they don't cover what glibc and MUSL provide, but it's ok for me
- ramrootfs (busybox based): 3Mbyte
-----------------------------------------------
- total 10Mbyte ------> 6Mbyte free!!!

What can I do with 6Mbyte? Well .. let's check it out

- tcp/ip, ip-v4 only, minimal (stripped down of all the congestion avoidance algorithms and misc)
- NFS-V3 client
- a "poor man" mini httpd web-server to export some good information to my browser
- mini sshd server running, it only accepts max 4 connections, it's enough to have a remote console
- gdb server running over the serial and over the network

With this machine I am having a lot of fun. But practically what is it used for?
Developing on a super low cost MIPS Linux Machine, and practically it's a weather station.

So you can understand why there is a "poor man" httpd server running 

[technix]

Developing on a super low cost MIPS Linux Machine, and practically it's a weather station.

Ummm you may want to upgrade the platform if you want to run anything more than that:

PIC32MZ-DA series has 32MB embedded DDR2 SDRAM in it and uses MIPS core. It also have XIP in both onboard and QSPI Flash (2MB + 128MB) so the kernel and libraries basically comes already "loaded in RAM" upon boot.
Loongson LS1C0300 uses external SDRAM, up to 128MB of it and it also uses a MIPS core.

[cgroen]

It must just be me, but how on earth should one answer this question  ?
I have made embedded systems with as low as 128 bytes of RAM and I have made embedded systems with 32 MBytes of RAM.
"How long is a piece of string?"

Or am I misunderstanding something in the question ?

[coppice]

It must just be me, but how on earth should one answer this question  ?

Whimsically. No other kind of answer will match that for value.

[SiliconWizard]

What the heck is an "embedded computer"?

There are probably millions of use cases. Your question doesn't make much sense.

Now if you're asking this, we can guess you don't have a specific application in mind. Possibly means you want to design some kind of generic "small computer", maybe as a dev tool, for others to use?
(Because if that were for a particular project of yours, surely you would know approximately how much RAM you would need.)

[TomS_]

is it overkill to set up 256MB SDRAM on AT91SAM9260 maxing it out?

Is it overkill to build a dump truck that can carry 400 tons of dirt?

Probably yes if you are talking to the local golf club. Likely no if you are talking to a mine.

[ImpulseBen]

So many variables. What is it you're testing / debugging? Add video analysis or any kind of AI and RAM gets eaten up real quick.