Transcript Chapter 5.1 (Nhat Phan)

Properties of memory cells:
1.Exhibits two stable states (binary 1 and 0)
2.Capable of being written into –to set the state
3.Capable of being read to sense the state
DRAM
•Dynamic
•Memory cell is simpler
•Requires data to be
refreshed periodically in
order to retain the data
SRAM
•Static
•No need to be refreshed
since transistors inside hold
the data as long as the
power supply is not cut off.
1. SRAM is static while DRAM is dynamic
2. SRAM is faster compared to DRAM
3. SRAM consumes less power than DRAM
4. SRAM uses more transistors per bit of memory compared to DRAM
5. SRAM is more expensive than DRAM
6. Cheaper DRAM is used in main memory while SRAM is commonly used
in cache memory
can be erased by exposure to strong ultraviolet light
is based on a similar semiconductor structure to EPROM, but
allows its entire contents (or selected banks) to be electrically
erased, then rewritten electrically, so that they need not be
removed from the computer (or camera, MP3 player, etc.).
an be erased and rewritten faster than ordinary EEPROM,
and newer designs feature very high endurance
Error correction is the
detection of errors
and reconstruction of
the original, error-free
data.
•No communication channel or storage
device is completely error-free
•As the number of bits per area or the
transmission rate increases, more errors
occur.
•Impossible to detect or correct 100% of the
errors
•There are several Error
Detection/Correction Methods
1.
One of the most effective codes for
error-recovery
1.
-
Used in situations where random
errors are likely to occur
Single parity bit can only detect error,
not correct it
Error-correcting codes require more
than a single parity bit
-
Hamming codes work well when we
can reasonably expect errors to be
rare events. (ex: hard drives)
-
Hamming codes are useless when
multiple adjacent errors are likely to
occur.