One example of a 27C256 equivalent:

The Winbond W27E257 EEPROM is a 27C256 equivalent, but electrically erasable instead.

I use these on my IBM 5155/5160/5170 motherboards.

You will still need an EPROM programmer (or other) to write to the W27E257, because the IBM 5155/5160/5162/5170 motherboard cannot write to EEPROM's.


W27E257-10  =  100 ns access time    (fastest 'speed')    (highest 'speed')
W27E257-12  =  120 ns access time
W27E257-15  =  150 ns access time    (slowest 'speed')    (lowest 'speed')


( Just a note about the above three speed ratings.  First, all are suitable for IBM 5155/5160/5162/5170 motherboards.  Next, the speed rating (e.g. access time of 120 ns) is akin to the speed rating on car tyres; it is effectively a maximum speed that the chip is to be run at.  The IBM 5155/5160/5162/5170 motherboards always run the ROM's at a fixed speed, irrespective of what ROM you fit.  So, on IBM 5155/5160/5162/5170 motherboards, there is no performance to be gained by using a 'faster' ROM than that specified by IBM for the motherboard.)