64kB

64 kilobytes (64 KB) is a unit of digital information equal to 64 × 1,024 bytes, or 65,536 bytes. In computing usage, 64 KB is typically understood as 64 KiB, since KiB stands for kibibyte (1,024 bytes). However, some contexts loosely use the decimal kilobyte (1,000 bytes), which would make 64 KB equal to 64,000 bytes. The distinction matters for precise storage calculations.

Historically, 64 KB defined a practical memory limit for many early microcomputers and computer architectures. A 16-bit address bus can address 2^16 = 65,536 distinct locations, which corresponds to 64 KB of addressable memory per contiguous address space. This constraint shaped operating systems, software design, and hardware layouts in the 1970s and 1980s. As systems evolved with larger address spaces, the nominal "64 KB" size became a hallmark of legacy platforms.

In modern computing, 64 KB is small relative to typical RAM and disk capacities, but remains a common unit in embedded systems, firmware, and software design. Some microcontrollers and real-time operating systems still define memory regions in 64 KB blocks for simplicity or compatibility with legacy code. Additionally, certain file formats, memory cartridges, or boot loaders may allocate data in 64 KB sectors or banks.

In summary, 64 KB equates to 65,536 bytes and historically represented the practical address space of 16-bit architectures, while continuing to serve as a convenient unit in constrained environments.