Memory Hierarchy

Question 1

What is a “memory system”

Answer 1

Answer: A memory system is a hierarchy of storage devices with different capacities, costs, and access time.

The system includes CPU registers, cache memories, and the main memory

Question 2

Describe an SRAM (static random access memory)

Answer 2

Answer:

• used for “cache memories”
• has six-transistor circuit
• aka LI, L2, L3 cache
• volatile (means data is lost when the power goes off)
• faster than DRAM

Question 3

Describe a DRAM (dynamic random access memory)

Answer 3

Answer:

• used for the “main memory”
• frame buffers
• 10 x slower than SRAM
• sensitive to light and electrical noise

Question 4

— —- —– is a storage technology based on flash memory.

Answer 4

Answer:

SSD (solid state drive)

Question 5

Describe an SSD. Cite an advantage of a solid state drive

Answer 5

Answer:

• based on flash memory
• EEPROM (electrically erasable programmable read -only memory)

Advantage:

• smaller physical size
• shorter access time

Question 6

A DRAM chip is organized as 64 supercells, each supercell comprising 8 DRAM cells. What is the minimum number of bits needed to specify the row and the column of a supercell?

Answer 6

Answer: 3 bits

DRAM = d x w bits 
d = supercell = 64 supercells
d = row x column (arranged in a rectangular array) 
d = 8 x 8 = 64 supercells

it takes 3 bits for the row (2^3)
and 3 bits for the column (2^3)

Question 7

A DRAM chip is organized as 64 supercells, each supercell comprising 8 DRAM cells. How many bits of data are transmitted simultaneously between the memory controller and the DRAM chip?

Answer 7

Answer: 8

Each DRAM chip is connected to some circuitry, known as the memory controller, that can transfer w bits at a time.

64 x 8 DRAM
d x w = DRAM
d = 64 supercells (in bits)
w = 8 bits per supercells

64 supercell x 8 bits / supercell = 512-bit DRAM