What this PROM is and where it fits
The AMD AM27S27/BWA is a 4Kbit (512 x 8) parallel PROM in a 22CDIP package. It stores firmware programmed once before deployment.
512 x 8 organization — firmware fit
Organized as 512 words of 8 bits each, this PROM holds exactly one 4 Kbit firmware image. That is enough for a boot loader, a small lookup table for a CRT monitor geometry correction, or a state-machine microcode for a PLC I/O module. The 22CDIP footprint is standard for 24-pin DIP sockets with two pins unused — verify the socket pinout against the original part before ordering.
Temperature grade and deployment environment
Rated for -55°C to 125°C case temperature, this is a military-temperature device. It belongs in avionics black boxes, missile guidance electronics, satellite telemetry boards, and downhole instrumentation where the ambient can swing from cold soak to hot operation. The ceramic hermetic package (22CDIP) resists moisture and outgassing, so it is also a candidate for sealed or high-reliability industrial enclosures.
Lifecycle and sourcing reality
Listed as Active, but this is a legacy bipolar PROM — AMD ceased volume production years ago. Real availability runs through surplus and independent distribution. We source and quote this part to order against an RFQ; availability and current pricing are confirmed at quote time. If the exact BOM line needs a drop-in replacement, the AM27S29/B2A is a surface-mount variant (same 4Kbit, 512 x 8, 70 ns) but requires a PLCC socket and board layout change — not a pin-for-pin swap. The AM27S25A/B3A at 35 ns is faster but also surface-mount. For a true through-hole alternative, the AM27S281A/BLA doubles the density to 8Kbit (1K x 8) at 50 ns and shares the same 22CDIP footprint, so it can replace the AM27S27/BWA if the firmware fits the larger space.