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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