GOOD Cache

What type of RAM is used for cache memory and is faster and more expensive?

SRAM

What type of RAM is used for main memory and is slower and less expensive?

DRAM

How many transistors make up an SRAM cell?

6 transistors

What component stores each bit in DRAM?

A capacitor and one transistor

Does SRAM need to be refreshed while powered?

No - it holds its value without refreshing

Is DRAM sensitive to voltage disturbances?

Yes - very sensitive and cannot recover if power is lost

What does RAS stand for and what does it do?

Row Access Strobe - selects the row in DRAM

What does CAS stand for and what does it do?

Column Access Strobe - selects the column from the row buffered by RAS

What trick does DDR DRAM use to increase speed?

It uses both edges of the clock signal to transfer data

How many bits does DDR5 transfer per cycle?

16 bits

What is the difference between volatile and nonvolatile memory?

Volatile memory loses data when powered off; nonvolatile memory retains data without power

How many times can a PROM be written?

Exactly once

How many times can an EPROM be reprogrammed?

About 1000 times - requires a special programmer device

How many times can an EEPROM be reprogrammed?

About 100000 times - no special programmer needed

What type of memory are SSDs and flash drives based on?

EEPROM

What is firmware?

Programs stored on ROM that run at power-up such as BIOS and bootloaders

What is the unit of reading and writing in an SSD?

Pages

What must happen before a page can be written in an SSD?

The entire block containing that page must be erased first

What is wear leveling in SSDs?

Distributing writes evenly across blocks to extend the SSD's lifespan

What is temporal locality?

A recently accessed memory location is likely to be accessed again soon

What is spatial locality?

A recently accessed memory location means nearby addresses will likely be accessed soon

What is a stride-1 reference pattern?

Accessing every consecutive element in memory - best possible spatial locality

What happens to spatial locality as stride length increases?

Spatial locality decreases

How does C store 2D arrays in memory?

In row-major order - row by row

For a 2D array a[M][N] which loop order gives better locality and why?

Looping a[i][j] row by row gives stride-1 and better spatial locality; looping a[j][i] column by column gives stride-N and poor spatial locality

In the sumvec function what kind of locality does the variable sum have?

Good temporal locality - it is reused every iteration

In the sumvec function what kind of locality does the array v have?

Good spatial locality - elements are accessed sequentially in memory

Why does good locality improve program performance?

Data with good locality is more likely to be stored higher in the memory hierarchy in cache which has faster access times