Intel MD27128A-20/B: A Deep Dive into the 128K UV-Eraseable EPROM

In the annals of computing history, the evolution of memory technology is a foundational narrative. Before the ubiquity of flash memory, the Eraseable Programmable Read-Only Memory (EPROM) was a revolutionary technology that enabled the development and firmware updates of countless electronic systems. The Intel MD27128A-20/B stands as a quintessential example of this pivotal technology, a 128-kilobit UV-erasable EPROM that powered an era of innovation.

Architectural Overview and Key Specifications

The "27128" in its part number directly denotes its capacity: 128 Kilobits, organized as 16,384 words by 8 bits. This 16K x 8 configuration was a industry-standard architecture, making it compatible with a wide range of 8-bit and 16-bit microprocessors of its time, such as the Intel 8088 and 8086.

The "-20" suffix signifies its performance grade: a maximum access time of 200 nanoseconds. This speed was critical for ensuring the processor did not have to enter wait states, thereby maintaining system performance. The "/B" designation often indicated a specific packaging or commercial grade variant.

Its most distinctive physical feature was the transparent quartz window located on the top of the ceramic Dual In-line Package (DIP). This window allowed high-intensity ultraviolet (UV) light with a wavelength of 253.7 nm to strike the silicon die inside. The UV energy would excite the electrons trapped in the floating gate transistors of the memory cells, effectively draining the charge and resetting every bit to a logical '1' state. This erasure process typically took 15-20 minutes under a dedicated UV EPROM eraser.

The Programming and Development Cycle

The MD27128A-20/B was a cornerstone in the development lifecycle of hardware. Firmware code, written in assembly or C, would be assembled/compiled into a binary file (.bin or .hex). An engineer would then use a dedicated EPROM programmer (or "burner") to write this data to the chip. The programmer applied higher-than-normal voltages (typically 12.5V or 21V on the programming pin) to pulse electrons into the floating gates, turning specific cells to a '0' state.

Once programmed, the quartz window would be covered with an opaque label to prevent accidental erasure by ambient light. The chip could then be inserted into its socket on the target board for testing. If a bug was found or an update was required, the label was removed, the chip was erased under UV light, and the entire cycle of programming and testing was repeated. This process, while iterative, provided a level of non-volatile reprogrammability that was revolutionary compared to its one-time programmable (OTP) predecessors.

Applications and Legacy

The Intel 27128 EPROM found extensive use across the technology landscape of the 1980s and early 1990s. It was the firmware storage medium of choice for:

Personal Computers: Storing the BIOS in early IBM PC clones and other systems.

Industrial Control Systems: Housing the control software for machinery and embedded systems where reliability was paramount.

Arcade Games: Containing the game code for countless classic arcade cabinets.

Peripherals and Test Equipment: Used in printers, modems, and scientific instruments.

Its legacy is profound. The EPROM paved the way for the Electrically Eraseable PROM (EEPROM) and ultimately NAND flash memory, which inherited the core concept of reprogrammable non-volatile storage but removed the cumbersome need for UV erasure. The Intel MD27128A-20/B remains an iconic component, symbolizing a hands-on, physical era of hardware engineering that laid the groundwork for the modern digital world.

ICGOODFIND: The Intel MD27128A-20/B is a classic 128K UV-EPROM that epitomized firmware storage in its era. Its 16Kx8 organization, 200ns speed, and UV-erasure mechanism were defining characteristics. It was instrumental in system development, BIOS storage, and industrial control, serving as a critical technological bridge between OTP PROMs and modern flash memory.

Keywords: UV-EPROM, Non-Volatile Memory, Firmware Storage, Intel 27128, UV-Erasable