Sometimes you have to search for the first portion of the part number. Usually the number at the end is just signifying how fast the RAM is, so in your case it's probably 80 ns. Sometimes extra letters have to be ignored too because they just represent different options. So for example, I might try searching for GM71C1000J or GM71C1000.
Searching for GM71C1000 gives some good results that indicate the chip is a 1-megabit chip. When they say something like 1048576 words x 1 bit, they mean it has 1048576 addresses that each represent a bit, so 1048576 bits = 1 megabit. With eight of those chips on a SIMM, it would indicate a total size of 1 megabyte.