Most memory components (e.g., integrated circuits such as DRAMs) are generally fabricated with 1 bit-, 4 bit-, or 8 bit-wide input/output lines. In any of these configurations, the components cannot operate as memories having an error correction code (ECC). There are, however, memory components fabricated with 5 bit- or 9 bit-wide input/output lines. These components operate as memories having an ECC, with the 5th (or the 9th) line used as an ECC line.
Memory modules (e.g., DIMMs (Dual Inline Memory Modules) or SIMMs (Single Inline Memory Modules)) comprise, among other components, a plurality of memory components. These memory modules may include memory components equipped with only 1 bit-, 4 bit-, or 8 bit-wide input/output lines; consequently, no ECC mode can be run on the memory module. To provide an ECC function, an extra memory component is provided that operates exclusively as an ECC, cooperating with memory components comprising 1 bit-, 4 bit- or 8 bit-wide input/output lines. Alternatively, memory modules may include memory components equipped with 5 bit- or 9 bit-wide input/output lines. In this case, ECC operation is available with each of the memory components.
The use of such memory components is exclusive—semiconductor memory components or semiconductor memory modules equipped with ECC capability can only be used in an ECC computer system (and not in a computer system lacking ECC functionality). Conversely, individual memory components or modules not equipped with an ECC capability can only be used in systems having no ECC functionality (i.e., they cannot be used in ECC-capable systems).