Questions

Getting the value of an environment variable is done by using `getenv()’. Setting the value of an environment variable is done by using `putenv()’

Mutex is the short form for ‘Mutual Exclusion object’. A mutex allows multiple threads for sharing the same resource. The resource can be file. A mutex with a unique name is created at the time of starting a program. A mutex must be locked from other threads, when any thread that needs the resource. When the data is no longer used / needed, the mutex is set to unlock.

DNA is copied during a process called Transcription. It is the first step of gene expression, in which a particular segment of DNA is copied into RNA by the enzyme RNA polymerase.

True, The luster of a metal is due to presence of free electrons. Luster means shine or soft glow. We know that metals have the quality of reflecting light from its surface.

Author of the book A journey  is Tony Blair

Adders are generally of five types:

1.Ripple Carry Adder:

The Ripple carry adder(RCA) consists of a building block named Half Adder(HA) which is cascaded to form a Full Adder(FA). These buildingblocks HAs and FAs are also the building blocks of all types of adders.The n full adders are cascaded to form n bit RCA.

The full adder has three input pins(input Ai,input Bi,carryin Ci) and two output pins(Sum and Ci+1).Its equations are:

Sum=Ai^Bi^Ci

Ci+1=Ai.Bi+Bi.Ci+Ai.Ci

2. Carry Lookahead Adder:

The Carry Lookahead Adder(CLA) reduces the delay as that in RCA. Let Gi=Ai.Bi, and Pi=Ai^Bi, then Ci+1=Gi+Pi.Ci.

The expressions for Sum and Ci+1 is then defined completely in terms of input pins rather wait for input carry to appear.

3. Carry Select Adder:

The carry select adder uses duplicate modules for each combination of input carry(i.e. 1 and 0).The multiplexers then select the appropriate sum and carry output according to the carry output of the preceding stages.

4. Carry Skip Adder:

The carry skip adder are as fast as carry lookahead adders which are the fastest adders but its spped decreases to about 20-30% if input operands are 64-bit or more. In these adders we divide the input bit stream into various blocks and make use of two observations:

-if each element of the two bit streams are unequal,i.e. Ai!=Bi than the carry input of the block is equal to the carry input.

-if each element of the two bit streams are equal,i.e. Ai=Bi than the carry input of the block is opposite of the carry input.

5. Carry Save Adder:

The carry save adder reduces the addition of three elements into addition of two elements,i.e. if you want sum of nine numbers it reduces it into sum of six numbers. In first step the sum of three numbers is calculated without bothering for the carry.During the second step only carry is calculated which is then added to the generated sum to give the required sum. 

23 chromosomes are in a human gamete.

Human somatic cells have 46 chromosomes(23 pairs) but a gamete(germ cell) gets half the amount, i.e. 23 chromosomes, (one from each pair). There will be half the number of chromosomes an organism has in its somatic cells (all other body cells except gametes).

For example in humans, the somatic cells contain 46 chromosomes which are the diploid number (2n) and each sperm and egg has 23 chromosomes where one of them is the sex chromosome.