640KB

640KB refers to a specific amount of computer memory, approximately 640 kilobytes. In the early days of personal computing, particularly with the IBM PC and its successors, this memory segment was a critical limitation and a source of much discussion and technical workarounds. The original IBM PC architecture, designed by Tim Paterson, allocated the first megabyte of memory into distinct regions. The lowest 640KB was designated for conventional memory, intended for the operating system and user programs. The remaining 384KB, known as the upper memory area, was reserved for system hardware like the video adapter and ROM BIOS.

As personal computers became more powerful and software more complex, the 640KB limit proved insufficient. Developers and users sought ways to overcome this barrier. Techniques such as memory management units (MMUs) and later expanded memory (EMS) and extended memory (XMS) specifications were developed to allow programs to access more than 640KB of RAM. The infamous "640K ought to be enough for anybody" quote, often attributed to Bill Gates, has become a legendary statement highlighting the perceived limitations of early computing architectures. While the 640KB barrier was eventually surpassed with subsequent hardware and software advancements, it remains a significant historical point in the evolution of personal computing.