ISRO2020-43

Question

Which of the following is an efficient method of cache updating?

• A. Snoopy writes
• B. Write through
• C. Write within
• D. Buffered write

Answer 1

Write through protocol updates (or invalidates) the shared data, as and when needed. It asks to update/invalidate via broadcasting (hence, not efficient, as it creates traffic)

Buffered write is an added functionality to write through cache. (Hence, not efficient, again)

---

Write back protocol is based on ownership of a block. (Read page 454 of Hamacher, 6th Ed). It also uses broadcast and creates traffic, hence, not efficient.
Though, the traffic generated is less than Write through.

---

Snooping:

the abilities of cache controllers to observe the activity on the bus and take appropriate actions  are called snoopy-cache techniques.

For performance reasons, it is important that the snooping function not interfere with the normal operation of a processor and its cache.

Hence, efficient.

 

Option A

Answer 2

$\underline{\textbf{Answer:}\Rightarrow}\;\mathbf{a.}$

$\underline{\text{Snoopy writes:}}$

In snoopy write, the cache controller monitors the operations of the other bus masters.

---

https://en.wikipedia.org/wiki/Snoopy_cache

Answer 3

option A) Snoopy Write – The abilities of cache controller to observe the activity on the bus and take appropriate actions .