CSCI 223 Quiz Memory Hierarchy Flashcards
RAM is traditionally packaged as a ?; basic storage unit is normally a ?
chip; cell (one bit per cell)
static RAM (SRAM)
each cell stores a bit with a four or six-transistor circuit; retains value indefinitely, as long as it is kept powered, relatively insensitive to electrical noise (EMI), radiation, etc.; faster and more expensive than DRAM
dynamic RAM (DRAM)
each cell stores bit with a capacitor, one transistor per bit; value must be refreshed every 10-100ms; more sensitive to disturbances (EMI, radiation, …) than SRAM; slower and cheaper than SRAM
DRAM and SRAM are ? memories because
volatile; they lose info. if powered off
nonvolatile memories retain value even if powered off - examples?
ROM, PROM, EPROM, EEPROM, flash memory
ROM
read-only memory: programmed during production
PROM
programmable ROM: can be programmed once after manufacturing
EPROM
erasable PROM: can be bulk erased (UV, X-Ray)
EEPROM (what’s on our system)
electrically erasable PROM: electronic erase capability
flash memory
EEPROMs with partial (sector) erase capability; wears out after about 100,000 erasings
bus
a collection of parallel wires that carry address, data, and control signals; typically shared by multiple devices
memory read transaction & describe
movl A, %eax
CPU places address A on the memory bus
main memory reads A from the memory bus, retrieves word x, and places it on the bus
CPU reads word x from the bus and copies it into the register %eax
memory write transaction & describe
movl %eax, A
CPU places address A on bus; memory reads it and waits for the corresponding data word to arrive
CPU places data word y on the bus
main memory reads data word y from the bus and stores it at address A
which is more complicated: memory read or memory write?
write
describe the “Power Wall”
2003 - decided to increase the number of cores, which decreases the speed but saves power
