Re: Why Do embedded processors have more Flash than RAM

For an embedded computer just think of Flash as disk and there is
always more disk than RAM. Except you can access the flash much faster
than disk so you can execute code right out of the flash with out
loading it in RAM as you would from a disk. That actually cuts down
the amount of RAM needed. On the other hand Flash has limited
write/rewrite life so your dynamic storage for temporary feequently
changing data is why the RAM is there at all. Just write out to Flash
what you want to keep around between power cycles, without power
refreshes RAM forgets.

So Flash is disk, with limits and bennifits.

-dcb

On Thu, 3 Nov 2005 07:48:18 +1100, "Phil W" <electropw@xxxxxxxxxxx>
wrote:

>Hi,
>
>Obviously your concept of processors comes from PC type system where all
>programs run in RAM.
>However, in embedded microprocessors programs generally run in flash, eeprom
>or rom, since there is no other storage medium that is non-volatile to hold
>the program whilst the power is off.
>In embedded systems there is generally no need to run programs in RAM since
>they are usually dedicated to a single application and do not need the
>ability to run different applications.
>Have a look at the AVR. It does not even give you the option of running a
>program from RAM, it's all assumed to be data.
>
>Phil
>
>
>"Maddy" <santhos@xxxxxxxxx> wrote in message
>news:1130945007.761856.138370@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
>> Hi,
>>
>> I cant help wonder why embedded processors have more Flash than RAM?
>> Right now, I am working with the AT91SAM7S, it has 256K Flash and only
>> 64K RAM. Why is this?
>> I am assuming we cannot run out of Flash. So if I had a program greater
>> than 64K what am I suppposed to do?
>>
>> Maddy
>>
>

.

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