Before you clip a programmer onto a BIOS chip, you need to know two things about it: how big it is and what voltage it runs at. Both are encoded in the part number printed on the chip. Get the size wrong and the programmer reads garbage or refuses the file; get the voltage wrong and you can damage a 1.8 V chip with a 3.3 V programmer. This guide explains how the major manufacturers build their part numbers, with the patterns that matter most for laptop repair.
What a part number encodes
Most SPI flash part numbers follow a similar structure:
| Part of the number | Meaning |
|---|---|
| Manufacturer prefix | Who made it |
| Series letters | Interface family and supply voltage range |
| Digits | Capacity, usually in megabits |
| Letters after the digits | Generation or technology, sometimes voltage |
| Package code | SOIC-8, WSON-8, USON and so on |
| Temperature and options | Industrial or commercial range, packaging, factory settings |
The full decoding of the trailing letters is in each datasheet's "ordering information" section. For repair, the capacity and the voltage family are what you must get right. The chips themselves are introduced in SPI Flash Chips Explained: The 25-Series BIOS Memory and described under spi flash.
Capacity
In most part numbers the digits after the series letters give the capacity in megabits:
- 32 → 32 Mbit = 4 MB
- 64 → 64 Mbit = 8 MB
- 128 → 128 Mbit = 16 MB
- 256 → 256 Mbit = 32 MB
Some manufacturers add extra digits after the capacity for the technology generation, so the capacity is the leading part of a longer number. The SPI Flash Size Calculator (BIOS Chip Mbit to MB) reads common markings and gives the size in bytes.
Voltage: the most important detail
Laptop boards use both 3.3 V and 1.8 V flash. Many newer boards use 1.8 V parts. A standard programmer such as the CH341A drives its pins at 3.3 V; using it directly on a 1.8 V chip stresses or damages the chip and can upset the board. Recognising 1.8 V parts by their part number is therefore essential.
| Manufacturer | 3.3 V families (examples) | 1.8 V families (examples) |
|---|---|---|
| Winbond | W25Q…JV, W25Q…FV | W25Q…JW, W25Q…FW |
| Macronix | MX25L… | MX25U… |
| GigaDevice | GD25Q…, GD25B… | GD25LQ…, GD25LB… |
| ISSI | IS25LP… | IS25WP… |
| XMC | XM25QH… | XM25QU… |
These patterns cover most chips you will meet, but always confirm the supply range in the datasheet for the exact part. When a chip is 1.8 V, use a 1.8 V adapter with the programmer, as explained in CH341A 1.8V Adapter: When You Need It.
Winbond
Winbond parts start with W25, followed by a series letter — Q for most current quad-SPI parts, X for older ones. Then come the capacity digits and a two-letter generation code that also tells you the voltage family: JV and FV are 3 V generations, JW and FW are 1.8 V generations. The letters after that encode the package and temperature range.
Example: W25Q128JV… is a 128 Mbit, 3 V part; W25Q128JW… is the 1.8 V equivalent.
Macronix
Macronix parts start with MX25, then a letter for the voltage family — L for 3 V, U for 1.8 V, R for some other ranges — then the capacity and further digits. MX25L12835F is a 128 Mbit, 3 V part; MX25U12835F is the 1.8 V counterpart.
GigaDevice
GigaDevice parts start with GD25. Q and B indicate 3 V families; LQ and LB indicate 1.8 V families. The capacity follows: GD25B128 is a 128 Mbit, 3 V part; GD25LB128 is a 1.8 V part.
Other manufacturers
You will also meet parts from ISSI, XMC, EON, Micron and several others. The same approach works: find the voltage family in the series letters, the capacity in the digits, and confirm in the datasheet. When in doubt about voltage, measure the chip's supply pin on a powered board — it tells you what the board gives the chip.
Measuring the supply as a check
If a marking is ambiguous, measure the chip's supply pin on a powered board, between the supply pin and ground. A reading close to 1.8 V settles the question; so does about 3.3 V. Do this with care, on the supply pin's decoupling capacitor rather than the pin itself where possible, and never with the programmer connected.
Package and temperature codes
The package code matters for how you connect to the chip:
- SOIC-8 — leaded, clip-friendly. Two body widths are common.
- WSON-8 / USON-8 — no leads, a pad underneath; clips do not fit. See the WSON guide.
- BGA — rare on laptops; needs special handling.
Temperature codes (commercial, industrial) do not matter for reading and writing, but matter when choosing a replacement chip: prefer the same or wider range.
When the programmer software disagrees
Programmer software identifies chips by their electronic ID. Sometimes it lists several possible parts for one ID, or a different name than the marking. That is normal: manufacturers reuse IDs across compatible parts. Choose the entry whose capacity and voltage match the marking. If the software cannot identify the chip at all, see CH341A Cannot Detect the Chip: Causes and Fixes.
Reading tiny or worn markings
Flash chip markings are laser-etched in small characters and can be hard to read, especially under flux residue or on a chip that has been heated. Clean the top with isopropyl alcohol, light it from a low angle so the etching casts shadows, and photograph it under the microscope. If part of the marking is unreadable, the visible part plus the board's schematic — which usually lists the flash part number — is normally enough.
Logging chip details
Write down the full marking of every flash chip you read, along with the board code. Boards of the same design sometimes ship with flash from different manufacturers; knowing which chips a board can carry tells you which IDs to expect in the programmer software and which voltage to prepare for before you even open the laptop.
Choosing a replacement chip
If a flash chip is physically damaged, replace it with the same part number or a compatible one with:
- the same capacity;
- the same voltage family;
- the same package and body width;
- support for the same read commands the board uses.
Program the replacement before fitting it, or in place with care.
Example: the chip that would not read
A technician clips a CH341A onto a laptop's BIOS chip and the software reads only random data. The chip is marked W25Q128JW. The "W" generation code means it is a 1.8 V part; the programmer has been driving it at 3.3 V. With a 1.8 V adapter added, the chip is detected immediately and two reads match. The chip survived; not every chip does, which is why reading the part number first matters.
FAQ
How do I know if a flash chip is 1.8 V?
From the series letters in the part number — for example JW or FW for Winbond, U for Macronix, LQ or LB for GigaDevice — and the datasheet.
What does the number 128 mean?
128 megabits, which is 16 megabytes.
Can I replace a chip with one from a different manufacturer?
Often yes, if capacity, voltage, package and command support match.
Why does my programmer show a different chip name?
Chips from different manufacturers can share IDs. Pick the entry matching your chip's capacity and voltage.
Does the temperature code matter?
Not for reading or writing. For replacements, choose the same or a wider temperature range.
Bottom line
Read the part number before you clip anything: the digits give the capacity, the series letters give the voltage family. Use a 1.8 V adapter for 1.8 V parts, confirm details in the datasheet, and choose replacements that match capacity, voltage, package and command support.