Complex sentence: Though 68010 had a loop mode, it was little used and 68020 replaced this with a proper instruction cache of 256 bytes, the first 68k series processor to feature onboard cache memory.
Split into simpler sentences: Though 68010 had a loop mode, it was little used. The 68020 replaced this with a proper instruction cache of 256 bytes, the first 68k series processor to feature proper onboard cache memory.