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Hardware Software Systems and Network Nathaniel Lee Weng ChuanIndividual Assignment TP016753

Table of Contents Table of Contents ............................................................................................................ 1

Gantt Chart ..................................................................................................................... 2

Abstract .......................................................................................................................... 3Section 1: Operating Systems, Question 2 ..................................................................... 4

Introduction ................................................................................................................. 4

Main Body .................................................................................................................... 4

Virtual Memory ......................................................................................................... 4

Paging ...................................................................................................................... 5

Demand Paging ........................................................................................................ 8

Swapping .................................................................................................................. 9

Conclusion ................................................................................................................. 10

Section 2 : Computer Systems Architecture, Question 2. ............................................. 11

Introduction ............................................................................................................... 11

Main Body .................................................................................................................. 12

Reasons for Registers ............................................................................................. 12

Types of Registers. ................................................................................................. 13

Conclusion ................................................................................................................. 15

Frequently Asked Questions (FAQ) ................................................................................ 16Section 1, Operating System ..................................................................................... 16

Section 2, Computer System Architecture ................................................................. 17

Limitations .................................................................................................................... 18

Bibliography / References ............................................................................................. 19

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Gantt Chart

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AbstractIn this modern age, many of us use computers to carry out our daily activities. But many of us do

not know how the computer carries out its memory management and uses Central Processing Unit(CPU) in order to carry out the processes necessary for the program to run. This report will cover

how the Unix operating system manages memory , strategies used, problems faced by memory

management and solutions to solve them. Besides that, this report will cover the computer systems

architecture such as the registers. Areas discussed would be reasons for registers, types of registers,

register size and a few other topics.

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Section 1: Operating Systems, Question 2

IntroductionThe operating system that I have chosen to cover memory management on is the Unix operating

system. Memory managements basically is the act of managing computer memory. In computers,memory is a very vital resource therefore it needs to be managed properly. Memory that is available

for the operating system to manage is the volatile cache in the Central Processing Unit, volatile

memory in the Random Access Memory and the non-volatile hard-disk storage. The part of the

operating system that manages it is called the memory manager. Its main task is to keep track of

which parts of memory are in use and which parts are not in use, to allocate memory to processes

when they need it and deallocate it when they are done, and to manage swapping between main

memory and disk when main memory is too small to hold all the processes. 1 There are many

different schemes in memory management.

Main Body

Virtual MemoryBefore virtual memory came about, computers had to have enough available memory or more

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Hardware Software Systems and Network Nathaniel Lee Weng ChuanIndividual Assignment TP016753memory to run the programs if not the programs would not be able to run due to lack of memory.

For example, if a program requires 32MB to run then the computer would need 32MB of available

memory or more to run that particular program. This was where virtual memory was introduced to

help solve this problem. Virtual memory is a feature of the operating system that enables a process

to use a memory (RAM) address space that is independent of other processes in the same system,and use a space that is larger than the actual amount of RAM present, temporarily relegating some

contents from RAM to a disk, with little or no overhead .2 How this works is that the program is

broken down to smaller pieces called overlays. The total amount of overlays that was formed from

the breaking down of a program may exceed the amount of physical memory therefore a larger

programs would be able to run successfully even though there is less physical memory than the

program needs to execute. Some of the overlays will be kept in the RAM and the other overlays of

the program will be kept in the disk. It is then the job of the operating system to choose which

overlays would be needed to be used in memory then swapping it from the disk to the memory as

shown in Figure 1.

Figure 1.

Source : http://cs.nyu.edu/~gottlieb/courses/2001-02-fall/arch/lectures/lecture-22.html

PagingMost operating systems that utilizes virtual memory for its memory management scheme will use a

technique called paging. In physical memory, some programs will be too large to be able to run.

With paging, programs are able to run even though it may not fit in the memory entirely. How this

works is that the program produces memory addresses based on things like indexing, base

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Hardware Software Systems and Network Nathaniel Lee Weng ChuanIndividual Assignment TP016753registers, and other values. These addresses are called virtual addresses and they form the virtual

address space. Then, these addresses are used in the Memory Management Unit (MMU) . The

Memory Management Unit is a part of the Central Processing Unit (CPU) that has a small amount

of memory that holds a cache table of recently used mappings of virtual addresses to physical

addresses.3

This table is known as the Translation Lookaside Buffer (TLB). Another table involvedin paging is the page table. The page table also holds the table matching virtual addresses to

physical addresses but the physical addresses here usually refer to the disk. In the page table, the

virtual address space is divided up into units called pages and the corresponding units in the

physical memory are called page frames. 4 The main reason for the page table is to map the pages

into the page frames.

Figure 2.

Source : http://cs.nyu.edu/~gottlieb/courses/2001-02-fall/arch/lectures/lecture-22.html

Figure 2 shows the relationship of the elements involved in paging. When a program is running, not

all the pages are in the memory at one time because the memory may not be big enough to

accommodate all of it. Therefore, pages are transferred in and out of the memory when needed by

the program. For example, when the program wants to access a virtual address, the page table will

be read to determine the physical address. Once the physical address is determined from the page

table, then the physical address and the virtual address will be written to the TLB. After the both

3 Internet.com, 2001.

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Figure 3 shows the workings of a multilevel page table. The first table on the left of the diagram is

the top-level page table. The top-level page table consist of all the index of the virtual address

assigned by the MMU. In order to locate the physical address, the top-level table's indexes are used.The entry located by indexing into the top-level page table yields the address or the page frame

number of the second-level page table. 7

Demand PagingThe Unix operating system utilizes the demand paging memory management scheme for its

operations. The demand paging memory management scheme is a more specific and detailed form

of paging. The principle behind demand paging is that the pages are only loaded into memory when

it is demanded by memory and not all at once. Therefore not all the pages are in memory at one

time. The pages brought in that consist of text, data and stack segments are brought in one at a time

as they get referenced.

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Figure 4

Source: http://cs.nyu.edu/~gottlieb/courses/2001-02-fall/arch/lectures/lecture-22.html

In the above figure, it shows that the virtual addresses are loaded into its respective locations on the

memory. When the memory needs another page from the page table it 'demands' it and the old page

will get swapped out for the new page. For example, based on Figure 4, the page with virtualaddress 24K-28K is in Frame 1 in the memory. So if it needs the page that has the virtual memory

of 28K-32K, then the page of virtual address of 24K-28K will be swapped out with 28K-32K page

because the memory 'demands' it. Only pages that exist in the page table will be swapped with the

one in the memory.

SwappingBesides virtual memory, the memory management scheme called swapping is used to run processes

when there is lack of physical memory to hold them. The excess processes will be taken out of the

memory and stored onto the disk. The main strategy of swapping consists of bringing in each

process in its entirety, running it for a while, then putting it back on the disk.

Figure 5.

The swapping system is illustrated in the above figure. At first, process A is in the memory inFigure 5(a). Later, process B comes into memory joined with process C. These processes either can

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be swapped from the disk or just newly created by the user. Process A is then swapped out onto the

disk to make room for another incoming process. In Figure 5 (d), it shows that process A has been

swapped out therefore leaving just leaving process B and C in the memory. Then process D take the

previous space of process A because if process A was still there, process D would not be able to fit

in memory as there is insufficient space for process D. Finally, process A comes in again and issituated at a different location on the memory.

Conclusion

In conclusion, the Unix operating system handles its programs with a very memory efficientmemory management system. It is able to run large programs without the need to have large

physical memory which is the Random Access Memory (RAM). This in turn, will benefit the users

of the Unix operating system. This is because firstly, the user does not have to buy larger RAM

which can be expensive. Secondly, the user will be able to run more programs simultaneously as

the Unix operating system has the ability to manage many programs and processes well and

effectively.

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Section 2 : Computer Systems Architecture,Question 2.

IntroductionThe most important part of a computer is of course is its Central Processing Unit (CPU). The CPU

is basically the brains of the entire computer. Most of the computers calculations take place here in

the CPU. 8 The primary part of the CPU is the Arithmetic Logic Unit (ALU), the Control Unit (CU),

and its registers. In this section, the part of the CPU that will be covered in this section would be

about the registers in the CPU. Registers are essentially a fast and small storage place within the

CPU that temporarily stores data to be processed by the CPU. 9 The registers are made out of flip-

flops. Also, depending on the type of CPU used the total number of registers can differ from each

one.

8 Internet.com, 2001.

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Main Body

Reasons for RegistersThe speed of which information is transferred between the CPU and the physical memory which is

the Random Access Memory (RAM) is very slow. For example, if the CPU were to calculate some

number and send the answer to be store onto the RAM while the CPU calculates another group of

numbers and then retrieves the previous answer to be calculated with the new answer it will take

too long for the process to be carried out. Therefore, to increase efficiency and save time, the

register exist to temporarily save these values in the CPU instead of the RAM.

Figure 6.

Source: http://schoolnet.gov.mt/keith.aquilina/resources/storage/Data_registers.htm

Figure 6 shows the components within the CPU. In a nutshell, the register is like a workspace for

the CPU to do its calculations. It holds values that the CPU is currently working with and stores

then onto the register itself. Then as soon as the calculations are processed, the information is sent

back to the main memory. For example, if the user wants to add 10 to a value in the memory

location, the CPU will load the initial value from the RAM into the register on the CPU. It then add

the 10 to the register and send the final value to the RAM from the register. This is done because

the CPU is unable to directly perform arithmetic functions in the memory and thus has to bring itinto the CPU. This transferring of information between the CPU and the RAM happens very fast.

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Types of Registers.The number of registers a CPU has depends on the type and model of the CPU. The total number of

registers in the CPU can vary from about ten to hundreds. The number of registers that the CPU has

and the size of register measured by the number of bits help determine the power and the speed of

the CPU. 10 For instance, a 64 bit CPU is a CPU where each single register is 64 bits in size.

Therefore, each instruction carried out by the CPU is able to have a maximum of 64 bits of data.

Which means that the workspace of the CPU is able to accommodate a unit measurement of 64 bits

of data for calculation before it sends it back to the RAM.

There many types of registers in the CPU but the main ones are:

Accumulator Register The accumulator register is a register that has a built-in adder that adds an input number to the

contents of the register. 11 If it were not for the accumulator register, the CPU would have to

write the results of each calculation back to the RAM only to read it again for the next

instruction. An example in the use of a accumulator register is the adding of a list of

numbers. The initial value of the accumulator register is set to zero, then each number will

from the list of numbers will be added to the accumulator register. Once all the numbers in

the list are added to the accumulator register, then the final value will be sent to the

memory.

10 Aquilina, K., Schoolnet.

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Hardware Software Systems and Network Nathaniel Lee Weng ChuanIndividual Assignment TP016753 Status Register

The status register which is also known as the flag register is a collection of flag bits

that

tells the CPU the current status of different mathematical operations. 12 The flags

assigned by the CPU each has its own individual meaning relative to its own differenttype of CPU the computer uses. Examples of types of common flags used by the CPU;

Z = Zero Flag The result of the mathematical operationequals zero.

C = Carry Flag The result of an operation has produced ananswer greater than the number of available bits

N = Negative Flag The result of a mathematical operation is anegative number.

V = Overflow Flag A register or memory location has

overflowed its number of available bits.I = Interrupt Flag Interrupts can be enabled or disabled by setting

or clearing this flag.

Instruction Register

The instruction register is a register in the CPU that holds an instruction as it is retrievedfrom the memory, the instruction is then interpreted within the instruction register

itself. 13 The instruction register is also involved in the instruction cycle. The instruction

cycle consists of four main task which are fetch instruction, decode instruction, execute

instruction and store the results .14 Firstly, the CPU fetches the instruction from the

RAM and places it in the instruction register. Then, the Control Unit of the CPU

decodes the instruction in the instruction register. The decode instruction is then sent to

the Arithmetic Logic Unit (ALU) to carry out mathematical and logical operations on

them. The results of the mathematical computation is then sent back to the instruction

register momentarily before it is sent to the memory for storage. This is cycle is then

repeated over and over again from the time the computer is started up till it shuts down.

Program Counter

The program counter is a counting register that increments the instruction cycle to obtain

12 WordIQ, 2010.

13 Parker, S., (ed), 2003.

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the program sequence from the memory locations .15 The program counter is another

register that is involved in the instruction cycle. The job of the program counter is to

take note of the address of the next memory instruction that is going to be executed by

the CPU next even before the current instruction is finished being executed. The

advantage of having the program counter as a register in the CPU is that it improves theoverall efficiency because it straight away know where the next memory address of the

instructions. Buffer Register

The buffer register's main task is to store data going to and from the RAM. As the name

suggest, the buffer register acts as a buffer to the CPU. This is so that the mathematical

and logical operations are not affected by values leaving and coming into the CPU.

ConclusionIn conclusion, the registers in the CPU play a vital role in the processing of instructions within the

CPU. These registers work together to allow data and information to pass through the CPU to be

processed. The registers also act as a medium for the Control Unit (CU) and the Arithmetic Logic

Unit (ALU) to communicate with the Random Access Memory (RAM). This is because all the

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Hardware Software Systems and Network Nathaniel Lee Weng ChuanIndividual Assignment TP016753instruction in the RAM has to be sent to the register first before it can be interpreted and executed

by the CPU. The size of the register will also determine how much data and instruction the CU and

ALU will be able to handle. Therefore, if the size of the each register has a larger size in bit then

more data and instruction is able to be executed by the CPU per instruction cycle. This would in

turn, maximize the amount of processing and increase the efficiency of the CPU.

Frequently Asked Questions (FAQ) Section 1, Operating System1. What is the difference between paging and demand paging in Unix?

In paging, the page frames brought into the main memory may not be in close proximity of

each other because the page frame will occupy the spaces available on the memory which

will not be necessary in one large space. But if it is able to find a large space available on

the memory, then the page frames might be close to one another. So the the page frames in

paging can be either be together one group on the memory or it can be scattered every

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where on the memory. Where as in demand paging, only the required page frames are

brought into the main memory and the idle page frames will be swapped out onto the disk to

make room for the incoming page frames. This gives the page frames more space available

and thus will the page frames will be in next to each another though the entire program will

not be able to fit onto the memory.2. Is it possible to have unlimited virtual memory since it is 'virtual'?

Even though the utilization of virtual memory may increase the amount of memory in the

physical memory, virtual memory is still limited because it has to be stored somewhere on

your computer. The user may be able to adjust how much virtual memory is allocated in the

disk but it still has a maximum value.

Section 2, Computer System Architecture1. Does a larger register size cause the computer to slow down because the time of a

instruction cycle takes longer?

A larger size register will not hinder the performance of the computer. Although the register

will be larger therefore there will be more instruction to interpret and execute, it will not be

any slower than a smaller size register. Nowadays, Central Processing Units are made with

even higher specifications and with the latest technologies. The instruction cycle happens so

fast no matter the size of the register. The slows down that may be experience is caused by

the data and instruction being sent to and received from the Random Access Memory

(RAM). The speed of which the RAM runs is very much slower that the CPU, therefore the

transferring of data to and fro is the cause of the sluggish computer.2. Are CPU registers considered as volatile or non-volatile memory?

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The registers in a standard CPU is considered as volatile memory. When there is a

sudden power cut, then the data stored in the registers will be lost.

Limitations1. Size of Random Access Memory When a program is ran, it will occupy space on the

RAM. Because of its fixed amount of RAM in computer, only a limited amount of programs

are able to be ran at one time. Even though, the user will be able to upgrade the RAM, the

user might still be limited to the amount of RAM the operating system can detect due to its

32 bit.2. Size of Virtual Memory The amount of virtual memory in the operating system is

limited to the amount allocated. Although user has the ability to manipulate the amount of

virtual memory, it is still limited by the space in the disk.

3. Speed of Random Access Memory Even though it may take a the CPU a very small

amount of time to carry out its instruction cycle, the computer will be slowed down by the

time it take the information that is already processed to be retrieved by the RAM.

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Bibliography / References1) Tanenbaum, A., 2001., Modern Operating System, 2 nd Edition, New Jersey, Prentice-Hall.

2) Regev, H., 2009, Virtual Memory [online], England, Search Storage, Available from

http://searchstorage.techtarget.com/sDefinition/0,,sid5_gci213300,00.html , [Accessed 11 th

September 2010]

3) Lectures, New York University, 2002, [online], Available from :

http://cs.nyu.edu/~gottlieb/courses/2001-02-fall/arch/lectures/lecture-22.html , [Accessed 11th

September 2010]

4) Internet.com, 2001, [online], Available from http://www.webopedia.com/TERM/M/MMU.html ,

[Assessed 11 th September 2010]

5) Tanenbaum, A., and Woodhull, A., 1997, Operating Systems Design and Implementation, 2 nd

Edition, New Jersey, Prentice-Hall.

6) Webster, 2000, [online], Available from

http://homepage.mac.com/randyhyde/webster.cs.ucr.edu/index.html , [Accessed 12 th September

2010]

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Hardware Software Systems and Network Nathaniel Lee Weng ChuanIndividual Assignment TP0167537) Elphinstone, K., and ,Ryzhyk, L., 2010, [online], Lectures, Australia, University of New South

Wales, Available from http://cgi.cse.unsw.edu.au/~cs3231/lectures.php , [Accessed 13 th

September]

8) Internet.com, 2001, [online], Available from

9) http://www.webopedia.com/TERM/C/cpu.html , [Accessed 13th

September]10) Shepley, P., 2010, What are the components of the CPU?, [online], USA, Wisegeek, Available

from http://www.wisegeek.com/what-are-the-components-of-a-cpu.htm , [Accessed 13 th

September]

11) Aquilina, K., Schoolnet, [online], Available from

http://schoolnet.gov.mt/keith.aquilina/resources/storage/Data_registers.htm , [Accessed 13 th

September 2010]

12) Jeff, Kioskea.net, [online], Available from http://en.kioskea.net/contents/pc/processeur.php3 ,

[Accessed 13 th September]

13) Farlex, 2008, Accumulator Register, [online], Princeton University, Available from

http://www.thefreedictionary.com/accumulator+register , [Accessed 13 th September]

14) WordIQ, 2010, Status Register, [online], Available from

http://www.wordiq.com/definition/Status_register , [Accessed 13 th September]

15) Parker, S., (ed), 2003, McGraw-Hill Dictionary of Scientific and Technical Terms, 6 th Edition,

USA, McGraw-Hill.

16) Agarwal, B., 2004, Instruction Fetch Execute Cycle, [online], Available from :

http://www.cs.montana.edu/~bosky/cs518/ife/IFE.pdf . [Accessed 13 th September 2010]

17) Daintith, J., 2004, A Dictionary of Computing, Encyclopedia.com, Available

from :: http://www.encyclopedia.com/doc/1O11-programcounter.html , [Accessed 13 th

September]

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