Why don't mothernboards have built-in RAM?

[jtr1962]

While the answer to this question was obvious when RAM was very expensive, I'm wondering why nowadays motherboard makers don't put a certain minimal amount of RAM(say 128 MB) on new motherboards. It would only add a few dollars to the cost and would definitely be a good selling point, especially if there was a feature in the CMOS to disable the onboard RAM in case it either went bad or you wanted to use something different.

Nowadays single-sided 256 MB DIMMs retail at around $20, which means they probably cost $10 to make. I would imagine each of the 8 RAM chips on the module wholesale for under $1, so putting 128 MB would add a big $4 to what it costs to make the board, and RAM is likely only going to get cheaper per MB in the future. Board space isn't much of an issue with this idea, either. We're only talking four small ICs here for 128 MB(and less in the future as RAM density improves). In the event RAM prices become high again, the chips can just be left off the M/B and the onboard RAM feature disabled in the CMOS. Including a slightly larger amount(say 256 MB), if space and cost allow it, will mean a good percentage of users won't need to buy RAM at all, but the DIMM slots will always be there for expansion or in case the onboard RAM fails.

This idea would have several advantages. First off you will be able to use the board by adding just a processor. Second, the total memory capacity for a given number of DIMM slots will be bit higher due to the presence of the onboard RAM. Third, the onboard RAM should be a bit more stable because it is connected directly to the board.

 

[blakerwry]

good idea... bad idea....

from my 486 and pentium days I KNOW onboard RAM is a bad idea....


(1) you can run into compatibility problems between the onboard and added RAM

(2) the onboard RAM is very limiting in the clock speeds you can run the motherboard at... hence, overclocking potential is very limited. So is the upgradability of the mobo.

(3) It adds another point of failure and instability that is hard to troubleshoot.



Personally, I was glad when mobo makers stopped adding system RAM to the motherboard... I was even more thrilled when L2 cache got put nto the processors and taken off the motherboard... and I am going to be even happier when memory controllers are integrated into the CPU.

 

[blakerwry]

When reading your post I was thinking that disabling RAM through the CMOS might not work correctly or would have problems... however, a jumper based solution would probably make me rest easier...

ie.. what if the RAM dies and you cant get into the BIOS to disable the onboard RAM...

or what if the RAM shorts out and causes the other chips not to be accessable...


a jumper (or series of jumpers) would be able to bypass the DIMM completely...
The way SDRAM works(in parrelell to all modules at the same time) might make this a bit harder... as adding jumpers will increase trace lengths... you might only get the option of using either the on-board RAM or your own RAM.. but not both... someone who better understands this could probably shed some light.

 

[Prof.Wizard]

Interesting idea.

 

[Tannin]

They used to. Really, really crappy ones in the awesomely regurgitative tradition of Amstead, Olivetti, Triumph-Adler and Commodore - to name but a few of the dry-heave vomit box makers of the distant past when the likes of Compaq and Hewlet-Packard were actually regarded as relatively good. The fact that neither of those last-mentioned companies has improved in the slightest should give you some vague conception of the prevailing standards of the day.

 

[Prof.Wizard]

Olivetti is no longer producing computers AFAIK. It has sold the operations and the brand name to someone else.

 

[CougTek]

It might be a good thing to include onboard RAM with the motherboards if it was some kind of low latency, large L3 cache level memory. Much like the L3 of the new dual PowerMAC for instance, but with something like 64MB or 128MB. This is a similar amount of RAM than the one found on many mainstream graphic card selling for not much. I'm sure it could be done on a motherboard for an acceptable price. But new chipsets would have to be developped to use that part of the memory (as some kind of cache) before the main RAM is touched.

The GeForce 4MX and Xabre 600 use faster than 400MHz low latency RAM modules and they don't cost an arm and a leg. I would gladly pay maybe 50$ more for a motherboard with a large amount of onboard RAM if the performance boost would be of 15% or more. I don't know how much of an improvement a large (64MB or 128MB) L3 cache would give though.

 

[Mercutio]

I'll be perfectly happy to sell you a couple of PC Chips SS7 boards with 16MB of SDRAM onboard. I think I know where I can find a couple. You can try 'em for a couple of days, and when you get done dry-heave vomiting, you can come back and tell everyone what you've learned.

More seriously, there are "issues" with onboard RAM. The first is that you're dedicating some of the in-design memory banks to non-upgradeable memory. The second is the classic "Some of the onboard RAM is bad" problem, the third is the even-more-classic "I just upgraded to a different board and found out all the parts I thought I have are built into my motherboard." Finally, do you think any motherboard maker that would actually do such a thing would actually use RAM that's anything like what we (builders and hobbyists both) would honestly consider using? We'll call that the "I didn't know they made CAS4 15ns PC1995 DDR memory" rule.

 

[Tannin]

Also (to add a little to Mercutio's answer), I'm sure that the last thing the motherboard manufucturers need would be to be forced to (in effect) participate in the RAM price sweepstakes. A manufacturer has to hold stocks of all components, and holding stocks of RAM is a scary business. The damn stuff shoots up and down all the time and owning any sensible amount of it is a really good way to lose money.

If you are just speculating, that is one thing. You are free to buy or hold off depending on how you read the market. But if you are including it as a part of your product, you have to keep a certain amount on hand lest you find the production line grinding to a halt for lack of just one component, and you have to buy more as you use it up, even when you are 90% certain that the price is heading downwards fast. Not nice.