27xx

27xx is a catalog prefix used by several electronics manufacturers to denote a family of integrated circuits, most often associated with erasable programmable memory devices, though the exact function varies by vendor and context. The term is commonly encountered in vintage hardware and archival references.

The most recognizable use of 27xx designations is for EPROMs, such as 27C64, 27C256, and 27C512. These devices store firmware or code for embedded systems and are typically packaged in 28-pin DIP or similar formats. Read operations occur at standard logic voltages, while programming requires a higher programming voltage and, in windowed EPROMs, exposure to ultraviolet light to erase the stored data. The "27C" prefix generally indicates parallel access memory with a direct address/data interface, and capacities in the series range from tens of kilobits to several hundred kilobits. In practical terms, 27C64 corresponds to 8 kilobytes of storage, 27C256 to 32 kilobytes, and 27C512 to 64 kilobytes.

Historically, 27xx EPROMs were widely used in 1980s and early 1990s electronics, including home computers, consoles, test equipment, and embedded controllers. As flash memory and EEPROM technologies emerged, new designs shifted away from 27xx EPROMs, but the parts remain of interest for restoration, preservation, and study of vintage hardware.

Beyond EPROMs, some manufacturers have used the 27xx prefix for other, unrelated product lines, but the predominant and most widely recognized association is with EPROM devices and their role in legacy firmware storage.