# MSI Plessey > Source: https://docs.barcoder.ai/docs/standards/msi-plessey > research date 2026-06-03 · extracted at 2026-10-03 > Publisher: Barcoder — encyclopedia of QR, barcode and payment-code standards Specifications: - [MSI Barcode — Wikipedia](https://en.wikipedia.org/wiki/MSI_Barcode) - [MSI Plessey barcodes — Cognex](https://www.cognex.com/resources/symbologies/1-d-linear-barcodes/msi-plessey-barcodes) ## Overview **MSI**, also known as **Modified Plessey**, is a numeric-only, continuous, variable-length 1D linear barcode symbology derived from the original Plessey Code [1][1]. It encodes only the digits 0–9 and supports no letters or symbols [1][1]. The symbology is not self-checking, so one or two optional check digits are normally appended for integrity [1][1]. Its primary application is inventory control — particularly the marking of storage containers and warehouse shelves [1][1][2][2]. ## History MSI was developed by **MSI Data Corporation**, basing the design on the earlier Plessey Code symbology [1][1][5][5]. Because of this lineage it is commonly called "Modified Plessey" [2][2]. (Plessey Code itself originated with the British Plessey Company.) ## Technical specification - **Character set:** digits 0–9 only; no alphabetic or symbol support [1][1]. - **Encoding:** each digit is converted to its 4-bit binary-coded decimal (BCD) representation [1][1]. A leading `1` bit is prepended and two trailing `0` bits appended to form the full bit stream [1][1]. - **Module structure:** each bit is printed as a bar/space pair three modules wide. A `0` bit is a 1/3-width bar followed by a 2/3-width space; a `1` bit is a 2/3-width bar followed by a 1/3-width space [1][1][5][5]. - **Start / stop:** start character is the bit `1` (pattern `110`); stop character is `00` (pattern `1001`) [5][5]. - **Self-checking:** MSI is a continuous symbology that is **not** self-checking [1][1]. - **Check-digit options:** MSI supports no check digit, or 1–2 check digits in several schemes [1][1][5][5]: - **Mod 10** — uses the Luhn algorithm; the most common option [1][1][5][5]. - **Mod 11** — two weighting variants: the IBM pattern uses repeating weights (2,3,4,5,6,7) and the NCR pattern uses (2,3,4,5,6,7,8,9) [1][1][5][5]. - **Mod 1010** — two sequential Mod 10 (Luhn) check digits [1][1][5][5]. - **Mod 1110** — a Mod 11 check digit followed by a Mod 10 check digit, giving maximum error detection [1][1][4][4]. ## Use cases MSI's dominant deployment is inventory and warehouse management: it is used to mark storage bins, containers, and especially **shelf edges** in warehouse and retail stockroom environments [1][1][2][2]. Its numeric-only nature suits internal stock-location numbering where alphanumeric data is unnecessary. ## Implementations - **[zint](https://github.com/zint/zint)** — C, ~771 stars, active in 2026. A barcode-encoding library supporting 50+ symbologies; lists "Plessey (MSI & UK)" / MSI Plessey among them [6][6]. - **[bwip-js](https://github.com/metafloor/bwip-js)** — JavaScript, ~2.4k stars, active in 2026. A pure-JavaScript port of Barcode Writer in Pure PostScript (BWIPP) covering 100+ types; exposes MSI as `msi` ("MSI Modified Plessey") [6][6]. (The widely used `python-barcode` library does **not** support MSI [3][3].) ## Comparison - **MSI vs. Plessey:** MSI is a direct derivative ("Modified Plessey") of the British Plessey Code, sharing the BCD-oriented heritage but redefining the bar/space module structure and check-digit handling [1][1][2][2]. - **MSI vs. self-checking codes:** Unlike self-checking symbologies (e.g. Code 39), MSI carries no built-in per-character integrity, which is why a Mod 10 or Mod 11 check digit (or both, as Mod 1110) is conventionally added [1][1]. - Among compact numeric codes MSI is bulkier than Interleaved 2 of 5 because each digit consumes a fixed BCD-derived width, so where density matters ITF is usually preferred; MSI persists mainly by inertia in shelf-labelling systems [1][1][2][2]. ## Status MSI is a **legacy, niche** symbology. It is no longer chosen for new general-purpose deployments but remains supported by commercial scanner SDKs and barcode-generation libraries (Cognex, Seagull/BarTender, zint, bwip-js), and still appears in established warehouse shelf-labelling systems [1][1][2][2][5][5][6][6]. ## Sources [1] [MSI Barcode — Wikipedia](https://en.wikipedia.org/wiki/MSI_Barcode) — Wikipedia, accessed 2026. [2] [MSI Plessey barcodes](https://www.cognex.com/resources/symbologies/1-d-linear-barcodes/msi-plessey-barcodes) — Cognex, accessed 2026. [3] [Supported Formats](https://python-barcode.readthedocs.io/en/stable/supported-formats.html) — python-barcode documentation, accessed 2026. [4] [MSI Plessey (Mod 1110) Generator](https://www.barcodegenerator.tech/Msi1110) — BarcodeGenerator.tech, accessed 2026. [5] [MSI Barcode](https://handwiki.org/wiki/MSI_Barcode) — HandWiki, accessed 2026. [6] [zint — A barcode encoding library](https://github.com/zint/zint) — GitHub (zint/zint), accessed 2026. [1]: https://en.wikipedia.org/wiki/MSI_Barcode [2]: https://www.cognex.com/resources/symbologies/1-d-linear-barcodes/msi-plessey-barcodes [3]: https://python-barcode.readthedocs.io/en/stable/supported-formats.html [4]: https://www.barcodegenerator.tech/Msi1110 [5]: https://handwiki.org/wiki/MSI_Barcode [6]: https://github.com/zint/zint ## Deployments _No country reports mention this standard by name._ ## Regions / aggregations not mapped to a single country - Universal