Commodore 128 Maximum RAM in Banked Mode

This guide examines the memory architecture of the Commodore 128 computer system. It details how the machine overcomes processor addressing limits to access its full physical memory capacity. The following sections confirm the specific amount of random access memory available when utilizing the native banked mode.

The Commodore 128 is equipped with 128 kilobytes of physical RAM, a significant upgrade over its predecessor, the Commodore 64. Despite having this amount of memory, the MOS Technology 8502 CPU can only address 64 kilobytes at any single moment. To solve this discrepancy, the system uses a memory banking scheme that swaps different sections of RAM into the CPU’s addressable space.

In the native C128 mode, the memory is organized into two main banks, each containing 64 kilobytes. Bank 0 is typically used for the operating system and BASIC, while Bank 1 is often reserved for user data and screen memory. By switching between these banks, the computer makes use of the entire installed memory pool. Consequently, the maximum amount of RAM the Commodore 128 can utilize in banked mode is 128 KB.

This banking capability allows for more complex software and multitasking operations that were not possible on earlier 64 KB systems. Programmers can store large datasets in one bank while executing code from another, effectively doubling the available workspace. Understanding this limit is essential for anyone developing software or configuring hardware for the Commodore 128 platform.