64Kbit parallel EEPROM — the legacy non-volatile workhorse
The Renesas / Intersil X28HC64S-15 is a 64Kbit parallel EEPROM organized as 8K x 8 bits, with a 150 ns access time and a 4.5V supply rail. It uses a full parallel address and data bus — 13 address lines and 8 data lines — which makes it a direct drop-in for designs that already have a memory controller or an MCU with an external bus interface. The 28-pin SOIC package keeps the board footprint compact for a parallel memory of this density.
The write cycle time is 5 ms for a word or a page write. That is slow compared to SRAM or Flash — you cannot stream data into this EEPROM at bus speed. The 5 ms write window means the host must poll the device's ready/busy status (or wait a fixed 5 ms) before attempting the next write. For storing calibration constants, serial numbers, or configuration tables that change infrequently, this is fine. For high-frequency data logging, a serial EEPROM with a faster page-write cycle or an FRAM would be a better fit.
This is a mature part with a stable supply — not a niche or obsolete component that forces a redesign down the line.