APPENDIX
92
SDRAM (Synchronous DRAM)
SDRAM is one of the Dynamic Random Access Memory (DRAM)
technologies that allow DRAM to use the same clock as the CPU host clock
(EDO and FPM are asynchronous and do not have clock signal). SDRAM
comes in 64-bit 168-pin DIMM and operates at 3.3V.
SIMM (Single In Line Memory Module)
SIMM socket is only 72-pin, and is only single side. The golden finger
signals on each side of PCB are identical. That is why it is called Single In
Line. SIMM is made of FPM or EDO DRAM and supports 32-bit data.
SIMM is phased out in current mainboard design.
SPD (Serial Presence Detect)
SPD is a small ROM or EEPROM device resided on the DIMM or RIMM.
Memory module information such as DRAM timing and chip parameters
can be stored into SPD so that BIOS can access it and use it to decide best
timing for this DIMM or RIMM.
UART (Universal Asynchronous Receiver/transmitter)
UART is built in a chip that controls the data sent to and received from a
serial port. A 16550 UART is now standard in most PCs, and supports modem
speed up to 57,600 bps and beyond and direct connect speed of 115,200
bps. Many UARTs have built-in errors in the internal code and just do not
work correctly with many external modems. UART is also found as the
serial interface on internal modem.
Ultra DMA
Ultra DMA (or, more accurately, Ultra DMA/33) is a protocol for transferring
data at 33.3MB/s between a hard disk drive through the computer’s data
path (or bus) to the computer’s random access memory (RAM). The transfer
data is twice as fast as the previous Direct Access Memory (DMA) interface.
The latest Ultra DMA has advanced to Ultra DMA/66 and Ultra DMA/100.
16.6MB/s x2 = 33MB/s
16.6MB/s x4 = 66MB/s
16.6MB/s x6 = 100MB/s
