Assignment 3
Page #246
Question One of Review Questions
1) What were the three technologies that combined to make modern computers possible?
During the time of Babbage, two technologies were present, and third about a century later.
a) Information was represented in a sequence of pulses of electrical current in a wire. The alphabet to represent communication was developed with a series of short and long pulses. The information was represented by electrical signals. An example of this technology was the telegraph of the 1800's.
b) Shortly the transistor was developed. The trasistor had three parts to it; they are the collector, the emitter and the base; a silicon based technology with impurities added. When an electrical signal is applied to the base, the current can pass through the other two elements. It has no moving parts, and very small compared to the technology of the telegraph type which is a type of on/off switch.
c) The third came around the turn of the century. Upon exposure to light, some chemicals change their properties. A chemical that reacts to light called a photresist is covered over the copper that is sandwiched between a non-conductive base and exposed to light through a negative mask, causing the combinations of base, copper and photchemical to harden. It is then the unhardened combination is washed away following a second chemical bath causing the uncovered copper to be etched. A third bath is used to wash away the hardened photresist leaving the wires photographically printed on the based board. This process saves considerable manufacturing time. The advatage of the mask, it can serve as a template that can be used as many times as needed.
Page # 257 Review Questions
1) What are the advantages of parallel representation of information in a computer? What are the disadvantages?
a) The advantages of parallel representation of information is increased complexity, running wires in parallel from the least significant to the most significant operating on the information as a unit rather than one bit at a time.
b) The disadvantage of parallel representation of information is decreased time, more complex, and you need to know in advance how to assign the wires to carry the information in parallel.
2) Multiply binary numbers 1011 x 1101, and check your answer by converting to decimal.
a)1011
1101
___
1011
0000
1011
1011
_______
10000101
Binary Multiplication
3) What is the important principle behind the working of a computer?
a) The important principle behind the working of a computer is Control. A computer is designed such that everytime it has to perform an operation, it will perform all operations and let the program set the switches to determine which results will be used.
4) How can we use AND gates as switches?
a) A switch can be regarded as like a traffic light. It controls the flow of traffic, in this case from left to right. When a vehicle wants to enter the flow out (right being out), the light needs to have the same value the vehicle has to allow it to do so. If it finds the vehicle has that value, it stops the ongoing flow of traffic to allow the vehicle to enter and be on it's way.
From left to right, the left is the input, the right is the output. In the middle, is the control wire of a switch. When the input is the same state as the control, control will allow the input out to the output.
An AND gate has two inputs, and one output. With an AND gate, to make it to the output state, the two inputs have to be true to be allowed out. If one of the inputs is neither, then they both do not gain entrance to the ouput. If the input is one, and the control is one, then the output becomes one. They have to have the value of one in order to complete the flow.
5) What are multiplexors and decoders, and why are they important?
a) A multiplexor is a multi-way switch. A multiplexor can have as many functions as you want. As the text discusses this concept, the authors chose to use a two function multi-way switch (as a multiplexor). One switch is an AND gate and so is the other. Each gate has two input lines and one output line. The input lines are represented on the left hand side of the gate, while the output line is on the right hand side. Of the AND gates, the input lines are referred to as upper and lower nput lines.
For the illustration of a multiplexor, the text uses two AND gates. One AND gate used to determine an addition problem, the other AND gate a multiplication problem. With the two AND gates for the multiplexor (multi-way gate) forms a circuit. A program wants to do a problem that involves addition. It sets the Select line that determines the value (sets the value) of the output to either one or zero.
For the text's example a switch is constructed in which the Select line determines, to set the output line Out to pass the value (or allow the flow) to that of line a or line b. If the Select line is one, the upper AND gate allows the flow to pass through making the Output the same as the a's input and not allowing the current to pass through the lower AND gate.
If the Select value is set to zero, the upper AND gate blocks the flow of a while allowing the flow of b, setting the Out the same value of b being zero.
Whatever the Select value is: one or zero, no matter how many lines there are for input and AND gates, or any other gates, the value of the input line equal to the Select value will pass through, blocking the others. Once the current that flows through them stops, they reset themselves back to a quiescent state.
b)Decoders are multiplexors in reverse. Rather, it takes a single input and a selection, and depending on the Select value, match the input to one of many output lines. So based on the value of the Select line being either zero or one.
Based on the Select value, multi-plexors have many inputs and one output. Decoders have only one input, and many outputs.
6) What do the d, g, and q lines in a latch do?
a) A latch is a circuit that can store a single one or zero bit of information. It can be built using three NAND gates and a NOT gate. A latch has two input lines that serve to set and reset its stored value, along with a single output line that yields the value of the "remembered" bit. The text also labels those input lines as (d and g). Each output of the NAND gates is represented by x, y, and z. When g=0, then circuit's lone output represented by q is unchanged, since the new value for z is the same as the old value of q. When g=1, the value of q is forced to be whatever the value of d is. so, accourding to the text, now that we have a latch, we now have a circuit that remembers.
Page #265 Review Questions
1) What do we mean by architecture of a computer?
a) The text refers to it as "that which is visible to an assembly language programmer", all that's there is the assembler, gernerating machine code on a statement for statement basis from the assembly language source code. When we design a computer, the decisions we make are feflected directly in the form that the machine langusge takes.
2) Describe the fetch-execute cycle.
a) The fetch-execute cycle is as the text says. "At each iteration of the cycle, the next program instruction is fetched from memory, and the statement is used to determine the action of the machine. The fetch-execute cycle is implemented in an orderly fashion by endowing the computer with a sense of time. The cycle continues until such time as the program signals the computer to halt, or the computer halts by itself due to a program error that makes further execution impossible.
3) Why did we dicide to address memory in Pip by bytes, rather than by bits?
a) The economic measure is one of complexity rather than money. 2 bits too small to be of any use, 32 bits to complex. the 8-bit byte would be the fundamental unit of information. 8-bits can express 256 different binary numbers, 256 bytes of memory, 8-bits to address memory.
4) What decisions were involved in the choice of Pip's instruction format?
a) How the machine language will be stored in memory using a single-address format and relying on a hardware accumulator to assist in calculations the accumulater being capable to hold 8-bits of information, storing instructions in two bytes, a 4-bit operation code, and 16 basic instructions.
5) Describe the ways in which Pip is more primitive than modern computers.
a) Pippin is not state of the art, in terms of sophisticated architecture, it is about 30 years behind the times, and in terms of complexity, it is about 100 times more simpler than the chip in a modern pc. A lack in other addressing modes, it's limited instruction set, and speed enhancement, like the use of pipelining, caching and it's size.
6) What are the 6 major parts of Pip and what are their functions?
a) The program counter which stores the 8-bit address of the current instruction in memory.
b) The instruction register, which stores the current instruction, divided into 8-bit pieces; the opcode in IRH, high order, leftmost bits and the operand in IRL, the low oreder, right most bits.
c) The decoder, which takes the instruction code as input adn produces several control signals as output.
d) The arithmetic logic unit, (ALU) which takes generally, two data inputs and a selection and based on the selection from the decoder, performs one of eight operations (+, -, *, /, AND, NOT, =, <) on it's data inputs.
e) The accumulator (ACC), is used to store the results of calculations from the ALU.
f) The random access memory (RAM), which takes an addrss and a read/write signal from the decoder and reads or writes information to the specified address.
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