What are 8 chip high density SIMMs?

Later, various accelerators featuring 68020, 68030, 68040, 68060 and PowerPC processors were made available by third parties. Such accelerators did not only have faster CPUs but also more and faster memory (on the most expensive boards 256 MB on two 128 MB SIMMs), real time clocks, IDE and SCSI ports and other enhancements.