It is part of the library defined by the ANSI standard, although not a part of the core C language standard. Keil includes implementations of standard library functions that they believe are relevant in 8051-based applications.

The folks at Keil are generally pretty sharp, and have probably hand-coded in assembly derivative-specific versions of memcpy() that leverage special features of the target device. Many devices feature multiple data pointers, auto-increment data pointers, etc. which can accelerate memcpy() operations.


Where is this example from? Do you have a link to the whole thing?

I've used memcpy() before on 8051's, but of course special care must be taken to avoid writing outside of the intended memory area. Especially since the Keil compiler does memory overlaying (necessary because of the 8051's anemic stack), writing out of bounds can cause subtle problems for which the source may be difficult to find.

In addition, simple use of memcpy() may be inappropriate in some cases. In the case of a DS89C450, for example, it may be necessary to increase the number of stretch cycles before copying from/to a slow external memory device.

Also, Keil's memcpy() is only implemented for the native architecturally supported memory of your device. Thus, you cannot use Keil memcpy() to copy to/from your I²C/SPI/one wire/other serial flash/EEPROM/NVRAM/other storage and so on.

--Sasha Jevtic

[EDIT: Erik already hit my last point before I did, which was the result of a telephone interruption. He also arguably stated it more cleanly than I did.]