A 4116 DRAM chip with a 250 ns access time would have a 500 ns cycle time, so could read or write 2 million words per second. The Acorn people called this a 2 MHz memory. You could have shorter cycle times in "column mode" where you pulsed the /CAS signal only to access words in the same row and the Acorn designers made good use of that for the Electron (reading 8 bits from a 4 bit wide memory) and the ARM based Archimedes (fetching instructions other than jump, load or store as well as loading the video and audio FIFOs).

From one DRAM generation to the next the cycle time might be different for chips with the same access time. This allowed me to make the 512KB Macintosh faster than the 128KB one (http://www.merlintec.com/lsi/mac512.html).