Fujitsu Siemens Computers D1691 Technical Manual page 65

Appendix I: Glossary
Cache: a temporary storage area for data that will be needed often by an application. Using a cache
lowers data access times, since the needed information is stored in the SRAM instead of in the slow
DRAM. Note that the cache is also much smaller than your regular memory: a typical cache size is
512KB, while you may have as much as 4GB of regular memory.
Cache size: refers to the physical size of the cache onboard. This should not be confused with the
cacheable area, which is the total amount of memory which can be scanned by the system in search
of data to put into the cache. A typical setup would be a cache size of 512KB, and a cacheable area
of 512MB. In this case, up to 512KB of the main memory onboard is capable of being cached.
However, only 512KB of this memory will be in the cache at any given moment. Any main memory
above 512MB could never be cached.
Closed and open jumpers: jumpers and jumper pins are active when they are "on" or "closed", and
inactive when they are "off" or "open".
CMOS (Complementary Metal-Oxide Semiconductors): chips that hold the basic startup
information for the BIOS.
COM port: another name for the serial port, which is called as such because it transmits the eight
bits of a byte of data along one wire, and receives data on another single wire (that is, the data is
transmitted in serial form, one bit after another). Parallel ports transmit the bits of a byte on eight
different wires at the same time (that is, in parallel form, eight bits at the same time).
DDR (Double Data Rate): is a technology designed to double the clock speed of the memory. It
activates output on both the rising and falling edge of the system clock rather than on just the rising
edge, potentially doubling output.
DIMM (Dual In-line Memory Module): faster and more capacious form of RAM than SIMMs, and
do not need to be installed in pairs.
DIMM bank: sometimes called DIMM sockets, because the physical slot and the logical unit are the
same. That is, one DIMM module fits into one DIMM socket, which is capable of acting as a memory
bank.
DMA (Direct Memory Access): channels that are similar to IRQs. DMA channels allow hardware
devices (like soundcards or keyboards) to access the main memory without involving the CPU. This
frees up CPU resources for other tasks. As with IRQs, it is vital that you do not double up devices on
a single line. Plug-n-Play devices will take care of this for you.
Doze mode: in this mode, only the CPU's speed is slowed.
DRAM (Dynamic RAM): widely available, very affordable form of RAM which has the unfortunate
tendency to lose data if it is not recharged regularly (every few milliseconds). This refresh
requirement makes DRAM three to ten times slower than non-recharged RAM such as SRAM.
ECC (Error Correction Code or Error Checking and Correcting): allows data to be checked for
errors during run-time. Errors can subsequently be corrected at the same time that they're found.
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