Internal Ram in 8051
the 8051 includes a certain amount of on-chip memory. On-chip memory is really one of two types: Internal RAM and Special Function Register (SFR) memory.
External Ram in 8051
As an obvious opposite of Internal RAM, the 8051 also supports what is called External RAM.
As the name suggests, External RAM is any random access memory which is found off-chip. Since the memory is off-chip it is not as flexible in terms of accessing, and is also slower. For example, to increment an Internal RAM location by 1 requires only 1 instruction and 1 instruction cycle. To increment a 1-byte value stored in External RAM requires 4 instructions and 7 instruction cycles. In this case, external memory is 7 times slower!
I.R.K.Seneviratne - Sri Lanka
internal and external memory
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avr is high speed cmpar to 8051.in 8051 there are less number of instructions
architecture
65536 bytes, because the 8051 family has a 16 bit external address buss.
The 8051 microcontroller has a maximum data memory capacity of 64 KB, which includes both internal and external RAM. Internally, it has 128 bytes of RAM and can be expanded to utilize external memory through its address bus. The architecture allows for addressing external RAM, but the practical limit often depends on the specific implementation and additional circuit design.
89s51 and 89s52 both are same version of 8051 microcontroller
The difference is that those MCUs that start with 80 are romless, those with 87 use EPROM erasable by light
Program Store Enable: The read strobe to external program memory.
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The 16 bytes (128 bits) at internal RAM locations 0x20-0x2F are bit-addressable.
The at89c52 are ones that are more advanced. This means that they are programmable compared to the 8051 which is not. So this makes a really big difference.