The Infineon CY7C0251-15AXCT is a 144 Kbit dual-port asynchronous SRAM organized as 8K×18. Two independent ports with separate address, data, and control lines let two bus masters — two processors, a processor and a DMA controller, or a processor and an FPGA — access the same memory array simultaneously. The 18-bit word width (8K×18) is a natural fit for systems that need a parity or tag bit alongside a 16-bit data word — common in networking equipment and RAID controllers where data integrity is checked in hardware. The parallel memory interface and 4.5–5.5 V supply rail place it in legacy 5 V logic environments, not modern 3.3 V or 1.8 V core designs.
15 ns access time — the timing decision
In an asynchronous system, the access time directly sets the minimum cycle time for a read or write operation. A 15 ns access means the SRAM can complete a random access in 15 ns from address valid, so a bus running at 66 MHz (15 ns period) can hit back-to-back accesses with zero wait states — provided the address hold and data setup margins are met. If your bus runs faster than 66 MHz, you need a faster SRAM; if it runs slower, this part has timing headroom.
Infineon lists the CY7C0251-15AXCT as Obsolete.
Package and handling notes
That is a fine-pitch surface-mount package.