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General Notes

Topic 6 Page 1

System Resources
Topic

Class Notes

Organised Notes

6
...
1 Identify the resources that
need to be managed within a
computer system
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- Measured in GB or TB
Processor speed
- Processor does all calculations in a computer system
...
If you have 2 ALUs you can do two operations
at once, etc
...

Bandwidth
- Measurement of how much data can be sent at same time in a certain time frame (also
called bitrate)
- Measured in bits per second (bps): Broadband = 16-100Mbps; LAN = up to 1Gbps (note: 1
Gbps = 1/8 GBps)
Screen resolution
- Measurement of number of pixels in height x width of display
- Measured in pixels
Sound processor
- Sound reproduction is done by a separate processor, freeing up the CPU to do other
calculations
...
1
...


Types of computers
• Mainframe
• Servers
• PCs
• Sub-laptops
• Cell phones
• Tablets
• PDAs
• Digital cameras

6
...
3 Identify the limitations of a
range of resources in a specified
computer system
...


6
...
4 Describe the possible
problems resulting from the
limitations in the resources in a
computer system
...

Multi-access and multi-programming environments should be considered as well as single -user
systems
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Or many users connected to the same network
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Single programming systems can only run one program/set of programs

Topic 6 Page 2

Resources of a Computer
6
...
1 Identify the resources that need to be managed within a computer system
...
In order to start a program, the processor gives a command to retrieve the
program from the hard drive
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The computer
places the program in RAM to make sure that the processor accesses the information faster and easier
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RAM has two main attributes, memory capacity and memory speed
...

Memory speed (in MHz) is the amount of time it takes RAM to get a request from the processor and then conduct that request (read or write data)
...

Secondary memory (in GB or TB) stores all programs and applications, even the operating system
...

Secondary memory is used to back up primary memory by copying it or using other data backup methods
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Secondary memory is needed to permanently store some data to a computer
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CPU (central processing unit) or the processor is the main chip in a computer responsible for carrying out all tasks
...
CPUs exist in anything that can run programs
...
A higher number can mean a faster processor,
but thanks to technology, processor chips have been made more efficient so now they can do more with less speed
...
Programs are written so that multiple cores can work on processing the data at the same time
...
Modern CPUs have atleast two cores, but can have four, eight and more
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A processor core is a processing unit that reads instructions to perform specific actions
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The machine instruction cycle runs in the core
...
A single core processor can only handle one thread at a time, so
the system rapidly switches between the threads to make it seem like the data is concurrently processed
...
This strongly increases the performance of a system that has concurrently running
applications
...
Some programs may not require this and thus is not
affected by having multiple cores
...
The amount of bandwidth determines the
efficiency and speed of internet activity (e
...
opening web pages, downloading files)
...
The wider the pipe, the greater the volume of water that can flow through it
...

Screen resolution is the number of pixels the screen can display horizontally and vertically
...
g
...
Screens that have different
sizes can still have the same screen resolution
...
A screen with a higher resolution but
same size to another screen will have a sharper image
...

Sound card is an internal circuit that provides input and output of audio signals to and from a computer through the use of applications
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The most basic sound card has to translate analog and digital information
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The GPU renders pixels into 2D and 3D graphics through RAM
...
It does this until all pixels form an image on the screen, which is dependent on screen resolution
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Cache (in MB) is a place to store something temporarily in a computing environment
...
Cache memory is RAM that a computer
accesses quicker than a regular RAM
...
Cache memory
stores frequently used program instructions, which enables fast access to these instructions and increases the speed of software
...
Network cards let a computer exchange data with the network
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Topic 6 Page 3

The motherboard is a circuit board located on the back side of a computer that connects all of the parts of a computer together
...
Motherboards are in phones, tablets and other small devices but they're often called
logic boards
...
1
...

Mainframes are computers used primarily by large organisations for important matters and large data processing
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Has vast amounts of primary memory and secondary memory
...

Can have 3-4GHz processor, as it is made up of multiple high spec PCs in parallel
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Has a single processor but multiple cores, so 1-4GHz speed
Has 2-16GB of primary memory
Has 256GB to 2TB of secondary memory
Sub-laptops or subnotebooks is a class of laptop computers that are smaller and lighter than a typical notebook
...

Has single or multi-core processor
Has 1-3GB of primary memory
Has limited secondary memory, but can be upgraded with SD card
Tablet computer is a portable personal computer, typically with a mobile operating system and LCD touchscreen display processing and a
rechargeable battery
...

Has single or multi-core processor
Has 1-4GB of primary memory
Has limited secondary memory, but can be upgraded with MicroSD card
Personal digital assistant (PDA) are a variety mobile device that functions as a personal information manager
...

Has single core processor
Has limited primary memory
Has expandable secondary memory through the use of memory cards

Topic 6 Page 6

CPU - RAM and Cache
6
...
3 Identify the limitations of a range of resources in a specified computer system
...
A DIMM is a dual inline module because it has two
independent rows of pins on each side
...
The average motherboard will have between 2 and
4
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From the hard drive, it is loaded into RAM
...
If memory is too low, it might not be able to hold all the data that the CPU needs
...
When this happens, it slows down computer
...
Increasing the RAM makes the computer run faster, as it does not have to travel from hard drive to RAM
...
Dynamic RAM (DRAM) is memory that contains capacitors
...
They have to be refreshed with electricity constantly, but the capacitors don't hold electricity for very long
...
If not
refreshed, they will forget information that they're holding
...
It also has capacitors but has a different speed
...
SDRAM runs synchronously, which runs faster
...

DIMMS come in different memory sizes and different speeds
...
The more bits that are transferred, the
faster the computer will be
...
DIMMs are faster than SIMMs, as they transfer twice the amoun t of data
...
8 Bits = 1 Byte
...

SDRAM could be labelled PC-100
...
33333
...
It has an 8 byte wide bus
...
This means that PC-100 RAM can transfer at maximum rate at 800 MB/s
...
The bottom notches are near the center of the module
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Rambus DRAM speed was 800 MHz but only had a 2 byte wide bus
...
Non-DDR only uses rising edge of clock cycle to transfer data
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DDR sends twice the amount of data
...
DDR may include both clock speed and total bandwidth in its name
...
This means that 2700 is its total bandwidth and 333 is its clock speed
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DDR2 is faster than DDR because it allows for higher bus speeds
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DDR2 can be labelled DDR2-800MHz PC2-6400
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DDR3 is twice as fast and uses less power than DDR2
...
You can't change DDR 2, 3, 4 on the
same motherboard
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Offers a higher range of speed than the rest of the DDRs
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The servers cannot go down for any reason
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It makes a correction if it needs to
...
Most RAM modules today are non-ECC because of advances in technology, which made non-ECC RAM more stable
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Using ECC memory is just a precaution to guard against any erros
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SRAM doesn't have to be refreshed and
is used in the CPU cache
...

CPU Cache is the CPU's internal memory and its job is to store copies of data and instructions from RAM that's waiting to be used by the CPU
...
The CPU always checks cache memory first to see if the data it needs is there
...
Cache memory is important because if CPU can access what it needs under faster cache, the faster
the computer will perform
...
The computer can run without CPU cache, but will become slower
Topic 6 Page 7

the computer will perform
...
The computer can run without CPU cache, but will become slower
because data can't be delivered to the CPU fast enough
...


CPU cache has three different levels
...
It runs at the same speed as processor
...

Level 2 cache or external cache is used to catch recent data accessed form the processor that were not caught by the level 1 cache
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If it can't find it then it goes to Level 3 cache
...
If CPU can' t find the data here,
then it goes to RAM to find data that it needs
...
In modern CPUs, level 2 cache is located on the processor
...
Level 3 cache is located on processor and is bigger than Level 2 but not as fast as Level 2
cache
...
Level 1 and level 2 are dedicated to
heir own CPU core
...
1
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Batch processing is when programs are batched together and then run as a group with minimal user interaction
...
Batch jobs are stored during working hours and then executed whenever the
computer is idle
...
A batch job continues until completion or
until an error occurs
...
g
...
B atch processing is
present in this because all of the data for purchases are collected and held until the bill is processed as a batch at the en d of the billing cycle
...
One program will be executed by the CPU while all the others wait
their turn
...
g
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This process is continued until all programs have finished running
...
The main purpose of multiprogramming is to maximize the use of CPU time
...
Multitasking loads tasks, which are smaller parts of a program, onto memory
...
Because tasks are smaller than programs, they are completed quicker
...

Multiprogramming and multitasking systems are CPU time sharing systems
...
The illusion of paralellsim is achieved when multiple jobs are executed by the CPU by switching very frequently between them
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Multiprocessing is processing multiple programs at the same time using more than one computer processor
...
A system can have more than one CPU core, making it a multiprocessing system
...
Multitasking and multiprogramming refer to the software
...
The program can be executed at the same time without interfering
with each other
...
In a multithreading system, several threads
can share one CPU core or run in parallel in a multi-core system
...
Without multithreading, if a requested task needed a long time to complete , the GUI would freeze
until the task was completed
...

Multi-access is a system in which several users are permitted to have apparently simultaneous access to a computer
...

A multi-access system must have the following characteristics:
Ability to communicate with multiple users and take input from them
Concurrent execution of programs with the ability to instantly switch from executing the program of one user to another
Ability to quickly find and make data stored on the hard disks available
Ability to protect data from unauthorized access

Topic 6 Page 9

Role of the Operating System
Topic

Class Notes

6
...
5 Explain the role of the
operating system in terms of
managing memory, peripherals
and hardware interfaces
...

The OS has to ensure that each process (program) runs in its own allocated memory space
...

Virtual memory is a feature of an operating system (OS) that allows a computer to compensate
for shortages of physical memory by temporarily transferring pages of data from random access
memory (RAM) to disk storage
...
We often refer to this as the folder-structure but in some OSes it is referred to as the
directory structure
...


User interface is used to interact with the computer to performs various tasks
...
The operating system then
translates the input/output and sends it to the correct memory address/folder address to be
processed
...

Graphical User Interface Operating System (Windows)
...

With a multi-user system, a time-slice is the set amount of processing time each user gets
...
Slices
(also called threads) are alternately processed to give the illusion of many tasks happening at
once
...
In general, interrupts are used to handle high-priority
conditions that require the interruption of the current code the processor is executing
...
1
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Scheduling is the method by which work is assigned to resources that complete the work
...
The algorithm used may be as simple as roundrobin in which each process is given equal time (for instance 1 ms, usually between 1 ms and
100 ms) in a cycling list
...

The policies what is to be done while the mechanism specifies how it is to be done
...
On the other hand, the decision of how long the timer is set for a
particular user is a policy decision
...

Multitasking, in an operating system, is allowing a user to perform more than one computer
task (such as the operation of an application program) at a time
...
Almost all of today's operating systems can do this
...

Virtual memory is a feature of an operating system (OS) that allows a computer to compensate
for shortages of physical memory by temporarily transferring pages of data from random access
memory (RAM) to disk storage
...

When using virtual memory, the OS needs to retrieve the data that was moved to temporarily
to disk storage; the only reason the OS moved pages of data from RAM to disk storage to begin
with was because it was running out of RAM
...
This process is known as paging or swapping and the
temporary storage space on the hard disk is called a pagefile or a swap file
...
The memory manager unit may use one of several
algorithms to choose which page should be swapped out, including Least Recently Used (LRU),
Least Frequently Used (LFU) or Most Recently Used (MRU)
...
An interrupt alerts the OS to a high-priority condition requiring
the interruption of the current code the processor is executing
...
This interruption is temporary, and, after the interrupt handler finishes, the
processor resumes normal activities
...

Polling is the process where the computer or controlling device waits for an external device to
check for its readiness or state, often with low-level hardware
...
Alternative to polling?: interrupts (signals generated by devices or processes to
indicate that they need attention)
...
g
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For the exams: know when & why
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1
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Advantages:
Security: A dedicated operating system ensures a higher level of security
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Customisability: Dedicated operating systems custom made to do a specific function at
maximum efficiency
...
Modify priorities: can make running some
devices easier to use or better suited to their audience
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6
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9 Outline how an operating
system hides the complexity of
the hardware from users and
applications
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This is used
to hide certain hardware details from users and applications (called abstraction)
...
Can be used is to make related devices
appear the same from the user’s point of view
...

A ‘drive letter; is a single alphabetic character A through Z that has been assigned to a physical
drive or drive partition in the computer
...
All computers with a hard drive will always have that default
hard drive assigned to a C: drive letter
...
g
...

A Java virtual machine (JVM interprets compiled Java binary code (called bytecode) for a
computer's processor (or "hardware platform") so that it can perform a Java program's
instructions
...


Topic 6 Page 11

Role of the Operating System
6
...
5 Explain the role of the operating system in terms of managing memory, peripherals and hardware interfaces
...
ALL OS are collections of
software and belong to the system software
...

Memory management is the act of managing computer memory and every instruction that is exececuted in the ALU that was loaded from the RAM
and not the hard drive directly
...
Only vital data should be kept in the RAM; the rest should be kept in secondary memory
...
The OS should stop
this, as it should dynamically allocate portions of memory to applications at their request and also free them for reuse when no longer needed by
the application
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Address binding is the process of mapping a logical address to a physical address
...
It should also convert the logical addresses into physical addresses whenever those addresses are ne eded by a process
...
The logical address is
generated by the CPU
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This address is seen by the memory unit and loaded onto the memory address register
...
The use of address binding helps to keep track of wher e the program is
located in RAM
...


Swapping is the general term for a mechanism in which a process or parts of program code that are not currently in use can be swapped
temporarily out of RAM and into a hard disk, and then later brought back into RAM to continue their execution
...

Paging allows the OS to use the secondary storage as if it was RAM
...
When the OS requests data from the disk, it exchanges a block of data (called a page) in RAM with a block of data on the disk
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Virtual memory is memory that appears to exist as main storage although it is actually in secondary storage, transferring between the two be ing
made automatically as required
...
There are three problems that virtual memory solves:
• Memory fragmentation - holes in memory which are due to the order of the programs
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A slice or a time-slice is the time
allocated to each user in a multi-access system or to a program in a multitasking system
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The interrupt handler is a software function that is performed when an interrupt is received by the computer
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The OS schedules the interrupt handler when time -slices for processes expire
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A
scheduler is a software that allows the scheduling and the tracking of computer batch tasks
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Scheduling is done to balance
the load on the system and ensure equal distribution of resources and give prioritization according to set rules
...
In modern multitasking OS, the execution of a process or thread can be restored at a later time if y ou stop it
...
When the scheduler goes
back to the lower priority task, it continues from the stored state
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Each device connected to a computer system wields a
device driver in order to communicate with the OS
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Device drivers are like translators between a program you're using and a device that the program wants to use somehow
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Device drivers are like translators between a program you're using and a device that the program wants to use somehow
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The operating hides the complexity of hardware resources from users while it also manages the interaction of processors, memo ry, data storage
and input/output devices
...
The OS efficiently
manages low level hardware in a way that the software can take advantage of the installed hardware
...
g
...

The OS managing hardware interfaces can be an example of abstraction because the OS allows the interaction between hardware
components and all application software, and hides all unnecessary details from the user and the application software
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These tasks include virus scans, backups, defragmentation and so on
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Factors such as CPU utilization, throughput, turnaround time, waiting time and response time need to be considered when selecting the best
scheduling algorithm for a situation
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A user account defines the privileges and access rights for one user
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An interrupt is a signal from a device or a program within the computer that causes the OS to stop the current task and decide what to do next
...
A software interrupt occurs when a program requests various services
from the OS
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Polling is the periodic checking of devices by a central device to determine their status
...


When you check your smartphone periodically to see if a notification comes up, this is polling
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The first approach is to take an existing OS and adapt it for the particular device
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The second approach is to design an OS that will fit the particular needs of the device
exactly
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Topic 6 Page 15

OS and Complexity Hiding
Drive letters can be an example of abstraction, as they correspond to real devices on the computer
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The user does not know the complexity that lies beneath this selection
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This is to maxi mise the
performance of the system, and the OS hides the complexity of this
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The Java Virtual Machine handles the details of code functioning on a specific hardware platform
...
The Java
architecture allows code to run on any machine on which the JVM interpreter has been installed

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