Week 2

Question 1

Describe the memory layout of a C program?

Answer 1

Command argc. and env. vars |
Stack Segment | Local or automatic variables, each function gets a frame. (grows high to low)
Heap Segment | Dynamically allocated variables.
Data Segments | Two data segments contain initialized/uninitialized global and static variables.
Text/Code Segment | Program/executable instructions.

Question 2

What is the difference between Pass-by-Value and Pass-by-Reference?

Answer 2

Pass-by-Value: Function creates local copy of variable (data object)
Pass-by-Reference: Function gets copy of address of variable (pointer)

Question 3

Why are memory hierarchies implemented?

Answer 3

To emulate a “large, fast and cheap” memory.

Question 4

Explain memory hierarchy?

Answer 4

Keeps data that processor requires now, with extra data, close to the processor in fast memory.

Question 5

How do you interface with a memory hierarchy?

Answer 5

Expose Hierarchy: CPU can access any level directly.
Hide Hierarchy: Single memory with single address space, hardware takes responsibility of storing data in fast or slow memory, depending on usage patterns.

Question 6

What is Locality of Reference?

Answer 6

The tendency of a processor to access the same set of memory locations repetitively over a short period of time.

Question 7

Describe Temporal and Spatial Locality?

Answer 7

Temporal: Reuse of specific data and resources in a small time duration.
Spatial: Use of data elements within close storage locations.

Question 8

How does a computer try to increase Locality of Reference?

Answer 8

Keeps most used data in SRAM (cache).
Refers to large DRAM for data not in cache.
Swap space (disk) only used when data cannot fit in DRAM.

Question 9

How does the C compiler store 2D arrays?

Answer 9

In a row-major order, e.g. all elements of row 0, then 1….