Scratchpad memory
Beginner
A fast on-chip memory that software fills and empties on purpose, instead of letting hardware guess what to keep.
Novice
Fast on-chip memory that software manages directly: a program or a DMA engine (a block that copies data without the processor’s help) explicitly moves data in and out. Unlike a cache it has no tags and never guesses, so its timing is predictable. Common in accelerators.
Expert
It saves the area and energy of tags and gives fixed latency, but the compiler or driver must plan every transfer. Sizing it is a joint hardware and software decision: too small and traffic to DRAM rises; too large and it dominates the die.