Question on EEprom chips

I'm having to reprogram some EEprom chips.
What does the suffix mean on chips. For example
ST M27C256-15F1 and ST M27C256-12F1
other suffix's I've seen are 10F1, 12F6
Other manufacturers also have different suffixes.(TI uses a 120JL or 25JL, etc.)
2nd question. My company got a new programmer, a Logical Devices XPRO-3000u, and my supervisor says I don't need to erase the old chips with a ultraviolet eraser, that the programmer will do it for me.
I found that the erase option on the programmer isn't available on these chips, and I was wondering if it could be done manually. Note: Filling with 00's works but the burner says the chip isn't blank, and trying to fill it with FF's just gets an error.
Any info would be appreciated, I know these chips are from the 80's
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UPNDOWN schrieb:

These are EPROM chips.
This means E_rasable P_rogrammable R_ead O_only M_emory The additional 'E' would designate an E_lectrical E_rasable...
You'll need the ultraviolet eraser.

Access speed. -15 = 150ns -12 = 120nsec

:-)
- Udo
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