Legacy memory is one of the hardest things to keep alive in a long-lived product. The IS41C16256-35K from ISSI is a 256-Kbit SRAM that still shows up on industrial, instrument and telecom boards — typically as a local buffer or scratchpad sitting next to an older MCU or ASIC. When one of these boards needs repair or a sustaining build, there is often no clean substitute, so the practical question is how to source the exact part safely.
Why this part is still on real bills of materials
A board designed around a given parallel memory device locks in three things: the address and data bus width, the access timing, and the physical footprint. Changing any of them means touching firmware timing, PCB layout, and sometimes the chip-select logic. For a product that is already certified or field-deployed, that risk is far larger than the price of the memory itself — which is why sustaining teams keep buying the original part number.
What to check before you buy
- Exact part number and suffix. Speed grade and package are encoded in the suffix; a different suffix can mean different timing or a different body size.
- Organisation and voltage. Confirm the bus width and supply requirement against the datasheet so the part matches your existing socket.
- Date code and lot. For mature parts the date code matters for traceability and for customers with age-sensitive incoming inspection rules.
- Quantity reality. Spot inventory moves. Treat a listed quantity as the current lot and re-confirm before you schedule a build.
Memory choices at a glance
| Situation | Practical choice | Why |
|---|---|---|
| Sustaining an existing design | Same part number, matched grade | IS41C16256-35K |
| Small non-volatile parameters | Serial EEPROM instead | 24LC16BT-I/SN |
| New design needing scratchpad | Modern SRAM / PSRAM | Better availability and documentation |
Buying tips for mature memory
Ask for the date code up front, request lot photos when the volume justifies it, and confirm the access-time grade in writing. If you are consolidating several legacy lines into one purchase, send the whole list rather than one line at a time — that lets a distributor quote the package and flag any line that is genuinely unobtainable before you commit.
We hold the IS41C16256-35K in spot inventory, and you can browse the wider memory and logic range for related devices.
Recommended next steps
If you are sourcing any of the parts mentioned in this guide, we can help you confirm stock, pricing, and lead times quickly.
- Upload your BOM — send your full parts list and receive a consolidated quote within 2 business hours.
- Browse related in-stock lines: Memory / Logic Devices.
- Contact our team for hard-to-find or end-of-life components.
About us & trademarks: JTDZ Tech (Shenzhen Jingteng Electronics Technology Co., Ltd.) is an independent distributor of electronic components. We are not an authorised distributor or representative of the manufacturers named in this article. Manufacturer and part names are used for indicative purposes only, to help identify the components discussed; all trademarks remain the property of their respective owners. Always verify specifications against the manufacturer's datasheet before design-in or purchase.
