can be programmed by the user with the appropriate equipment. Once programmed, the data and instructions can’t be changed

is programable with the added advantage of being reprogrammable but to be reprogramed, the entire chip must first be erased using special tools

The presence or absence of charge in a capacitor is interpreted as a binary 1 or 0

DRAM stores data as a charge on a capacitor

data values are transferred from the capacitor to the bit line

data values are transferred from the bit line to the capacitor

When the address line is selected, the charge stored on the capacitor is fed out onto a bit line

…. destroys the bit value stored on the capacitor, so the data word must be restored (rewritten) after each read

Even when DRAM is not read, the contents must not to be refreshed (read and rewritten) every few milliseconds, because the charge on the capacitor gradually leaks away

A voltage signal is applied to the bit line(1 for high, 0 for low)

A signal is then applied to the address line, allowing a charge to be transferred to the capacitor

a DRAM requires the supporting refresh circuitry

…. requires the supporting refresh circuitry

SRAM is static because stored bits do not need to be refreshed

in SRAM The data bit is stored on cross-coupled inverters

if noise degrades the value of the stored bit, the cross-coupled inverters restore the value

DRAM cell is … and … than SRAM cell

DRAM is … dense and … expensive than SRAM

smaller cells=… cells per unit area

SRAMs (used for cache memory ) are generally faster than DRAMs (used for main memory)

SRAMs, and DRAMs are all volatile memories