128Kb

128kB is a unit of digital information equal to 128 kilobytes, which is 131,072 bytes. In modern usage it is more common to express this quantity in binary terms as 128 kibibytes (KiB). The 128kB designation appears frequently in the documentation of older computing systems and embedded devices. For example, many early home computers such as the Commodore 64 or the ZX Spectrum had 128kB of RAM or ROM, and this capacity was frequently marketed as "128K" or "128 kilobytes."

In the context of firmware and system firmware, a 128kB ROM is often large enough to store a full operating system bootloader or minimal operating system code. Embedded microcontrollers with 128kB of Flash memory can implement complex real‑time control applications or run lightweight operating systems such as Zephyr or FreeRTOS with multiple tasks and peripheral drivers.

The size of 128kB was a practical compromise for many low‑cost devices, balancing memory cost against performance. It signified a threshold beyond which applications could include more sophisticated features, memory protection, and larger buffers. In modern systems, 128kB is still used as a benchmark for small microcontrollers and as a base size for many firmware images. Because of the binary definition, the phrase "128kB" can sometimes generate confusion with the decimal 128,000 bytes; therefore, technical documentation usually clarifies the definition by specifying "128 KiB."