Hector Martin

Fun fact: people like to say that unlike Flash memory, RAM can be read or written to one byte at a time, but that's a lie. A typical DIMM's memory array can only be addressed in 64KiB blocks! Writing one byte means reading 64K, modifying one byte, and writing 64K! (1/n)

In fact, *reading* is a destructive operation in RAM. Reading one byte means reading 64K (which destroys it), then writing back the 64K untouched! However, the RAM chips perform this read-write operation when directed, so the 64K doesn't have to go out via the bus and back. (2/n)

The difference is that RAM doesn't wear out, so nobody cares that it works this way. The RAM can also combine a long sequence of reads or writes, sequential or scattered, within one page, into one read, a sequence of I/Os, and a write back to the array. (3/n)