Chapter 6, Problem 36RETC

Explanation of Solution

TLB:

Translation Look aside buffer is special type of cache that is used to store the contents of the page table.

The content of the TLB cache includes pairs of virtual page number, physical frame numbers.

Effective Access time (EAT):

• EAT is a measure of Hierarchal memory performance.
• A weighted average that utilizes the hit ratio and the relative access time of the levels present in successful order of the memory hierarchy is called as effective access time.
• The actual time of the access is based on the technology that is utilized to access the contents present at each level of the hierarchy.

Formula for the effective access time:

The formula for effective access time where the memory contains two levels that includes a main memory and the cache memory is obtained as shown below:

$\text{EAT}\text{=}\text{H×2}\times {\text{Access}}_{\text{c}}\text{+}\left(\text{1-H}\right){\text{×Access}}_{\text{MM}}$

In the above formula,

$\begin{array}{l}\text{H}\text{=}\text{cache}\text{hit}\\ {\text{Access}}_{\text{c}}\text{=}\text{cache}\text{access}\text{time}\\ {\text{Access}}_{\text{MM}}\text{=}\text{Main}\text{Memory}\text{access}\text{time}\end{array}$

Since all the pages reside at the memory the time taken to access will be doubled because every access made in the main memory requires a page table access.

TLB improves EAT:

• The performance speed of the page lookup can be improved using TLB.
• The entries of the TLB buffer include the virtual page number and the corresponding frame number is required to make up the process.
• It does not contain any location constraints in the mapping the page frame