Any letters before the "27" part is usually manufacturer info and not too important.
If it has a "C" after the 27, it means CMOS.
This means they are usually newer, faster, and require less power to program and run.
You can replace a "non-C" with a CMOS eprom,
but it is not recommended to replace a CMOS with a non-CMOS.
The digits after the 27 or 27C are the eprom size in BITS
2716 = 16kBits = 2Kbytes
2764 = 64kbits = 8Kbytes
27c512 = 512kbits = 64kbytes
27c010 = 1 Mbit = 128Kbytes
If the next code is the letter "A" , it means it programs at a lower voltage.
For 2716A and 2732A that means 21V rather than 25V.
For 2764A and 27128A that means 12.5V rather than 21V
Starting with 27256, pretty much every eprom after that programs at 12.5V.
After that there is usually a dash " - "
Then the eprom speed.
There is no standard for eprom speed markings, so common sense prevails.
Older eproms (2716-2764) range from 100-450 ns.
So 2716-1 would be 100ns, 2716-35 would 350ns, 2732-45 would be 450ns
Sub-100ns are only found on 1Mb eproms and up.
So a 27c040-45 would be 45ns, 27c010-120 would be 120ns
(...although I have seen 27c040-12, meaning 120ns ).
In fact, the fastest eproms I've ever seen are 45ns.
You can always use a faster eprom, but not a slower one.
(...I know some application that need 120ns or better, so a 150ns won't work...)
Hope this helps.
Cheers,
Steph