Tuning memory resources

Tuning memory resources

The SCO OpenServer system is a virtual memory operating system. Virtual memory is implemented using various physical resources:

Physical memory as RAM chips; sometimes referred to as primary, main, or core memory.
Program text (machine code instructions) as files within filesystems on disk or ramdisks.
Swap space consisting of one or more disk divisions or swap files within filesystems dedicated to this purpose. The individual pieces of swap space are known as swap areas. Swap space is also referred to as secondary memory.

Depending on the system hardware, there may also be physical cache memory on the CPU chip itself (level-one (L1) cache), or on the computer's motherboard (level-two (L2) cache), and on peripheral hardware controller cards. If recently accessed data (or, for some L1 and L2 caches, machine instructions) exists in this memory, it can be accessed immediately rather than having to retrieve it from more distant memory.

Write-through caches store data read from memory or a peripheral device; they ensure that data is written synchronously to memory or a physical device before allowing the CPU to continue. Write-back caches retain both read and written data and do not require the CPU to synchronize with data being written.

NOTE: Most L2 caches work with a limited amount of main memory. Adding more RAM than the cache can handle may actually make the machine slower. For some machines with a 64KB L2 cache, this only covers the first 16MB of physical memory. See the documentation provided with your computer or motherboard hardware for more details.