Memory

Question 1

Define ROM (read only memory)

Answer 1

-Memory that cannot be written, it holds data.
-ROM holds the instructions for a computer to start once the power is on.

Question 2

Define non-volatile in terms of memory

Answer 2

Retains data even when power is off.

Question 3

Define access time

Answer 3

the time it takes for the correct data to become available after an address is presented to the device

Question 4

How has memory performance changed over time?

Answer 4

Manufacturers have made access time as short as possible
from 500ns to 5ns or less

Question 5

How can memory devices be categorised?

Answer 5

-programmed by the user
-programmed by the manufacturer

Question 6

Define ROM

Answer 6

Read only memory.
-Data cannot be overwritten after manufacturer has built the program into the chip.

Question 7

What are the benefits of ROM

Answer 7

-Low cost
-High volume
-stable program

Question 8

What are the most common user-programmable devices?

Answer 8

-EEPROM (electronically erasable) - written byte to byte
-Flash Memories - written in a block

Question 9

What are some pros of EEPROM over Flash memory?

Answer 9

-EEPROM can be reporgrammed multiple times
-non-volatile
-faster than flash memory in write and erase operations

Question 10

Define EPROM

Answer 10

Erasable programmable read only memory
-has a glass window where strong UV light erases the data
-or can erased via electrical pulses
-EEPROM/UVEPROM

Question 11

Explain the importance of access time

Answer 11

If the access time is longer than required by the processor, errors occur.
If the access time is shorter than required, the device will be more expensive than necessary

Question 12

What are the main differences between Flash and E2PROM?

Answer 12

-E2PROM: individual locations can be erased
-FLASH: erasing circuits are common to a block of memory cells
-Flash is more cost effective

Question 13

Why is the number of write/erase cycles important?

Answer 13

Certain software can wear out memory if written incorrectly

Question 14

Define RAM

Answer 14

Random access memory- volatile memory that stores information from the microprocessor or other digital devices

Question 15

Define SRAM

Answer 15

Static RAM
-uses transistors and latches to store data
-volatile

Question 16

Define DRAM

Answer 16

Dynamic RAM
-based on capacitors and stores each bit of data into a cell

Question 17

Define NVRAM

Answer 17

Non-volatile RAM
A type of flash memory that contains an internal battery to maintain data when the power supply is off

Question 18

Define FRAM

Answer 18

-Ferroelectric RAM
A low power non-volatile memory with fast RAM
-Has the best parts of Flash/EEPROM and RAM

Question 19

What is the difference between FRAM and other memory devices?

Answer 19

-FRAM stores data in ferroelectric material
-Write and read access times are 2-3 digit nanoseconds
-Is non-volatile but has very fast access

Question 20

Give an example of an FRAM device

Answer 20

Ramtron FM1608

Question 21

Compare SRAM and DRAM

Answer 21

SRAM: Uses transistors
Very fast
more expensive
DRAM: Uses capacitors
slower
less expensive
-cannot retain data as long

Question 22

Compare SRAM to EEPROM

Answer 22

SRAM has infinite write/erase cycles

Question 23

What is considered in terms of memory when designing a microcontroller circuit

Answer 23

-what will happen when the power supply is off when a location is being written
-microprocessor supervisory circuits help prevent critical data being lost

Question 24

What is the smallest unit of data?

Answer 24

Byte

Question 25

Explain the write operation

Answer 25

-Address decoder selects specific location in memory
-memory gets write command
-data is bussed and stored in memory address

Question 26

Explain the read operation

Answer 26

Address decoder receives a code from address bus
-specific location in memory is selected
-memory gets read command and data is copied and outputted

Question 27

What is the difference between ROM and PROM?

Answer 27

ROM:
-permanently programmed by manufacturer
PROM:
-works the same but is programmed by user

Question 28

Why is unlimited read/write cycles good?

Answer 28

Every time data is erased and written, it doesn’t affect the lifespan of the memory. Better endurance

Question 29

Compare non-volatile memory to volatile memory in terms of endurance, cost and access time

Answer 29

Volatile (RAM):
-very fast access times
-(almost) unlimited read and write cycles
-generally cheaper

Non-volatile:
-Generally slower, access time depends on type of memory
-Limited write cycles which affects lifespan
-typically more expensive