# Hardware Questions

Q:

What are the different hazards? How do you avoid them?

There are situations, called hazards, that prevent the next insturction in the instruction stream from executing during its designated clock cycle. hazards reduce the performance from the ideal speedup gained by pipelining.

There are three classes of Hazards:

1. Structural hazards: It arise from resource conficts when the hardware cannot support all possible combinations of instructions simultaniously in overlapped execution.

2. Data Hazards: It arise when an instruction depends on the results of previous instruction in a way that is exposed by the overlapping of instructions in the pipeline.

3.control hazards. it arise from the pipelining of branches and other instructions that chage the PC.

Subject: Hardware

4955
Q:

Why crystal is a preferred clock source?

Because of high stability, large Q (Quality Factor) & the frequency that doesn't drift with aging. Crystal is used as a clock source most of the times.

Subject: Hardware

4884
Q:

What are set up time & hold time constraints? What do they signify? Which one is critical for estimating maximum clock frequency of a circuit?

Suppose your flip-flop is positive edgetriggered. time for which data should be stable prior to positive edge clock is called setup is called setup time constraint.

Time for which data should be stable after the positive edge of clock is called as hold time constraint.

If any of these constraints are violate d then flip-flop will enter in meta stable state, in which we cannot determine the output of flip-flop.

there are two equation:

1. Tcq + Tcomb > Tskew + Thold

2. Tcq + Tcomb > Tskew + T - Tsetup

Tcq is time delay when data enters the flip flop and data comes at output of flip flop.

Tcomb is the logic delay between two flip flop.

Tskew is the delay of clock to flip flop: suppose there are two flip flop, if clock reaches first to source flip flop and then after some delay to destination flip flop, it is positive skew and if vice versa then negative  skew.

so if you take 2 eq you will see that setup time is the determining factor of clock's time period.

Subject: Hardware

4868
Q:

Which processor structure is pipe lined?

All x86 processors have pipelined structure.

Subject: Hardware

4517
Q:

What is called scratch pad of computer?

Cache Memory is scratch pad of computer.

Subject: Hardware

4338
Q:

Where does the Real mode on the CPU come from?

The original 8086, which only had 1 MB of memory. This megabyte is split into low memory for IRQ tables, application memory and high memory.

Subject: Hardware

4284
Q:

Why address bus in unidirectional and data bus is bidirectional?

Because there is no need address traansaction between processor and peripheral device but data bus is needed because data has to be read and write

Subject: Hardware

4205
Q:

Can ROM be used as stack?