why do plc's have so little memory still?

jraef said:

And the CPU was about an 18" cube!

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I still work on a few of these....customer slow to upgrade due to original cost involved on the PLC3, they want to get maximum ROI.
We actually supplied equipment with the PLC3 CPU rack being more cost than the whole rest of the furnace system.

ganutenator said:

3) automation direct is kinda the harbor freight of automation.

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Beg to differ. We have been exclusively using their PLC's and HMI since 2010. We have over 60+ C-more ver.7 HMI's installed in harsh manufacturing environments in 4 different countries. (Think Chemicals & sub fabs). Never had to replace a single HMI, CPU, or an Direct logic I/O card to date.

In Contrast, we have had to replace over 20+ Panel View+ Series 6 12" screens (Cost over $5,000 Each), Several Rockwell/AB Remote I/O modules, Ethernet modules, Relay output cards etc. The newest and the largest Automation direct C-more is under $2,000 with better Resolution and speed.

There are PLC's still running Semiconductor Manufacturing operations using PLC's having less than 2 Meg of memory. Some are still using PLC 5's. So what is it that you are wanting to do with all this memory? Just curious.

I agree with those that say it is BS. Our motion controllers have more memory than the PLCs that control them. Memory is cheap. The problem is retaining it during power off situations. In our case we have a special memory that keeps retained memory but we cannot retain all of the memory. We have 1MB allocated to the program memory alone.
Our new RMC200 has 16 MB reserved for curves or cam tables. We have over 12M 4 byte entries for capturing data.

I think we have a total of 256MB of ECC ram. ECC is the kind of ram that Xeon processors must use. ECC ram will correct errors.

What we have found over the 30+ years of making motion controller is that ram gets cheaper and cheaper and bigger and bigger. Todays small rams will be as expensive or more expensive than larger rams because of lack of demand. It makes no sense to skimp on ram.

I read something about lack of address lines. That isn't a problem with modern CPUs.


BTW, we have had many more problems with static rams than we have had with dynamic rams.

all this memory

skyfox said:

So what is it that you are wanting to do with all this memory? Just curious.

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All this memory?
Reminds me of some of the earlier Bill Gates quotes.

Most of the time, I am quite happy that the automation world moves more slowly than the computer world.

But the fact that we are still working w/ KBytes at this place in time, is f..ng b.s.