# ST Microelectronics Papers: Sample Questions 25 - 27 of 40

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## Question number: 25

### Write in Short

If sampling frequency is fs then what will be the signal frequency if they both are having same characteristics?

### Explanation

• Based on Nyquist theorem, sampling frequency should be twice of signal frequency.

So,

• Nyquist theorem is used for distortionless transmission of signal through channel. If sampling frequency is less than twice of signal frequency then aliasing effect will take place. Due to aliasing effect signal gets distorted.

## Question number: 26

### Write in Short

A clock is late by 1 minute 27 seconds in a month. Then how much will it be late in 1 day?

### Explanation

1 minute = 60 seconds

1 hour = 60 minutes

1 day = 24 hours

1 month = 30 days

In 30 days clock is late by 1 min and 27 seconds, i. e. by 60 + 27 = 87 seconds

In 30 days clock is late by 87 seconds

1 day clock will be late by (? ) seconds?

=

= 2.9 seconds

So, clock will be late by 2.9 seconds in one day.

## Question number: 27

### Write in Short

Give the relation between hit ratio and effective memory access time.

### Explanation

• Effective memory access time = hTc+ (1-h) Tm

• Here, h = hit ratio
• (1 - h) = miss ratio
• Tc = cache access time (time to access information from cache)
• Tm = memory access time (time to access main memory)
• The cache access time is less then memory access time. For example, If cache access time is 100 nano seconds and hit ration is 0.8 then memory access time will be 100 + 100 = 200 nano seconds and miss ratio will be 1 – 0.8 = 0.2
• So, Effective memory access time = 0.8100 + 0.2200

= 80 + 40

= 120 nano seconds