When to allocate to external memory RAM or ROM

[kumarkde]

When there is both Internal RAM and External RAM in the project and space available in both, how do you choose to allocate variables between External RAM or Internal RAM ? Is there is general rule ?

[jimblumberg]

Normally "External" RAM is larger but also with much slower access. So generally if both are available then you would choose "Internal" RAM. However you might choose the external for large arrays, or seldom used variables.

Jim

[itCbitC]

Btw what is the difference between external and internal RAM?

[CommonTater]

Btw what is the difference between external and internal RAM?

Spelling?

[jimblumberg]

Normally when talking about internal and external ram you are dealing with micro-controllers. The internal ram is the ram contained in the micro-controller while the external ram is located externally.

Jim

[Yarin]

When there is both Internal RAM and External RAM in the project and space available in both, how do you choose to allocate variables between External RAM or Internal RAM ? Is there is general rule ?

No. This is entirely dependant on the device(s) in question.
As Jim mentioned, this is almost always only dealt with embedded devices, like PICs, etc.. I've never heard of a common PC with external RAM that stood on it's own (only ever, that which belonged entirely to an independent device).

[jimblumberg]

I've never heard of a common PC with external RAM that stood on it's own

In the dark ages of PC's, before Windows, to increase memory above 640k, memory cards were often used. These cards were also considered external memory. And since they ran at system bus speed they also had slower access times than the ram on the mother board.

Jim

[kumarkde]

Thnx Jim. And how about external and Internal Flash memory ? What functions to allocate to what.

[jimblumberg]

And how about external and Internal Flash memory ? What functions to allocate to what.

That depends on your compiler and micro-controller. For the external memory the functions you use would also depend on the compiler, how this memory is connected to the controller and many other factors.

Jim

[Yarin]

In the dark ages of PC's, before Windows, to increase memory above 640k, memory cards were often used.

Heh, wudduya know.

And how about external and Internal Flash memory ? What functions to allocate to what.

As has already been said...

This is entirely dependant on the device(s) in question.

However, if you were to start a new thread, maybe giving more info, like what exactly you're dealing with, you'd get some answers you can use