entire comp sci flashcards
1
Q
main job cpu
A
The Fetch-Decode-Execute cycle is the main job of the CPU.
2
Q
instructions in fde cycle
A
In a program, each machine code instruction takes up a slot in the main memory. These memory locations each have a unique memory address. The program counter stores the address of each instruction and tells the CPU in what order they should be executed.
3
Q
what does cpu do to execute program
A
To execute a program, the program code is copied from secondary storage into the main memory. The CPU’s program counter is set to the memory location where the first instruction in the program has been stored, and execution begins.
4
Q
process of fde
A
The CPU checks the program counter to see the next instruction to execute.
The program counter gives a memory address to where the next instruction is
The CPU fetches the instruction from this memory address
The instruction is decoded and executed.
The program counter increments by 1
The cycle is repeated indefinitely
5
Q
job alu
A
Arithmetic calculations
Logical operations
Comparisons between values
6
Q
job cu
A
The control unit organises the fetch decode execute cycle, including managing the other components in the processor.
also controls flow of data inside and outside cpu
7
Q
registers
A
Small amounts of high-speed memory in the CPU used to store small amounts of data needed for processing
Includes the address of the current instruction, the next instruction to be executed, and the results of calculations
8
Q
job cache
A
A small amount of high-speed memory physically inside the CPU.
Temporarily holds small amounts of data which the CPU will reuse often.
Speeds up the system - does not have to wait for some data in memory to be fetched
Level 1, 2, 3 cache - 1 is the fastest, most expensive, and has the lowest amount of storage, likewise, 3 is the slowest, least expensive but contains the most amount of storage
9
Q
what does von neumann arch state
A
Data and instructions are stored as binary
Data and instructions are both stored in primary storage
Instructions are fetched from memory one at a time and in order
The processor decodes and executes an instruction, and then does the same for the next instruction
This will continue until there are no more instructions
10
Q
5 registers in von neumann arch
A
the program counter (PC)
the memory address register (MAR)
the memory data register (MDR)
the current instruction register (CIR)
the accumulator
11
Q
program counter
A
the program counter (PC) holds the memory address of the next instruction to be fetched from primary storage
12
Q
mar
A
the memory address register (MAR) holds memory address about to be used by CPU
13
Q
cir
A
the current instruction register (CIR) holds the instruction that is currently being decoded and executed
14
Q
mdr
A
the memory data register (MDR) holds data/instruction fetched from memory, or data about to be written to memory (primary)
15
Q
accumulator
A
the accumulator (ACC) is a special purpose register and is used by the arithmetic logic unit (ALU) to hold the data being processed and the results of its calculations
16
Q
clock spd
A
The clock speed is measured in gigahertz (GHz) and represents how many fetch-decode-execute cycles happen per second. 1 GHz = 1 billion cycles.
17
Q
too highclock spd
A
However, a CPU which cannot keep up with its clock will corrupt its data. A very fast clock speed will cause the CPU to overheat and thermal throttle, reducing its performance to stop it from melting
18
Q
why cache is there
A
Transferring data in and out of memory takes much longer than from cache. Therefore, placing frequently accessed data in the cache results in everything using that function being executed much faster. The more cache there is, the more data can be stored closer to the CPU.
19
Q
l1 l2 l3 cache
A
L1 is usually part of the CPU chip and is both the smallest and the fastest to access. L2 and L3 caches are bigger than L1. They are extra caches built between the CPU and the RAM. Sometimes L2 is built into the CPU with L1.
L2 and L3 caches take slightly longer to access than L1.
20
Q
cons of cache
A
However, cache is very expensive (L1 costs ~£1 per kilobyte), is limited by the space of the CPU, and is very small, so cannot be a full replacement for memory.
21
Q
num cores
A
A CPU has multiple cores on it. CPUs with multiple cores have more power to run multiple programs at the same time.
However, doubling cores does not double clock speed. Some headroom is needed to communicate between each core.
22
Q
embedded system
A
An embedded system is a small computer inside of a larger system.
Embedded systems have one specific function which they run.
23
Q
prim storge
A
Primary storage consists of RAM (random access memory) and ROM (read-only memory).
24
Q
general process comps
A
General process computers are designed to access the Internet, play games, play videos, and write programs. These all require applications to run. Tablets, phones and consoles are now increasingly classed as general process, as they now can run several applications.
25
avantage embd sys
Advantages of these systems include they require less power to run and are cheaper to make as their processors are not as powerful.
26
where can programming be done on embd system
They are not reprogrammable either - all the programming is done in manufacturing.
27
rom
ROM is non-volatile (retains its data after being powered off) and is usually often now only used to boot the computer, providing for the BIOS or UEFI.
28
exmpl embd system
Examples of embedded systems include GPS systems, digital watches, fitness trackers, washing machines, microwaves and more.
29
sec strgae
Secondary storage is non-volatile, meaning it retains the data written to it even when offline.
30
ram
RAM is smaller storage than 2ndry, but is much faster as it does not have moving parts or have to retain that information.
The more RAM a computer has, the more programs and instructions it can store simultaneously.
it is volatile
31
virt mem
Virtual memory is an area of secondary storage which is used as an overflow for when memory is filled up.
When RAM is full, data which would have gone to memory goes to an area of the disk drive. However, virtual memory is very slow.
32
hdd
An HDD (magnetic) has high capacity and involves flipping magnetic polarity to store bits. It is fairly fast to access.
33
usb
A USB drive (solid state) is tiny in comparison but very portable so is useful for transferring files between people and their computers.
34
ssd
An SSD (solid-state) has high capacity and involves trapping electrons to store bits. They are extremely fast to access
35
optical
Optical storage devices like CDs and DVDs use a laser to scan the tracks, and when light reflects back, it will either reflect from ‘lands’ - representing 1, or not reflect in ‘pits’ - representing 0
36
do embd sys have 2nd strg
Embedded systems may not need these as the instructions to run them are usually in ROM
37
formua 4sound file size
Sound file size = sample rate x duration (s) x bit depth
38
formula text file size
Text file size = bits per character x number of characters
39
formula image file size
Image file size = colour depth x image height (px) x image width (px)
40
hex to denary/binary
write down the hex digits, and convert them into nibbles which can then easily convert into denary.
F is 15 (1111 in binary)
0 is 0
41
denary/binary to hex
opposite of hex to binary/denary
42
adding binary digits
0 + 0 = 0
0 + 1 = 1
1 + 1 = 0, carry 1
1 + 1 + carried 1 = 1, carry 1
43
binary shift
A shift of 1 to the left means multiply by 2.
A shift of 3 to the left means multiply by 2^3 = 8
A shift of 1 to the right means divide by 2
A shift of 3 to the right means divide by 2^3 = 8
44
character set
character sets are collections of characters a computer recognises from their binary representation
45
ASCII
7bit binary code
reperesnts 128 total characters
extra bit added to start of binary code (0) so the character is 1 byte storage e.g
( (0 - extra bit) 1111111)
good for english lang
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Xtended ascii
8 bit binary code
256 characters represnted
good for langs with slightly more letters like french which has é
47
unicode
16bit/32bit binary code
millions of represntable characters
e.g all langs, emojis
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image
An image is represented as a series of pixels, again, represented as binary. Each pixel has a specific colour, represented by a specific code (can be a hex value).
49
img size+quality affected by
the image’s size and quality can be affected by the colour depth and resolution.
50
working out colour depth from bit depth
A black and white image has a bit depth of 1. This means it can only represent two colours - 2^1 = 2 colours.
An image which uses 10-bit depth can represent 2^10 = 1024 colours.
Colour depth = range of colours available.
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size of img
Size, or dimensions, is how many pixels the image contains, in terms of height by width.
52
esimting size of file
The size of an image file can be estimated using:
the image height in pixels
the image width in pixels
the colour depth per pixel
53
resolution
Resolution is used to describe how densely packed the pixels are.
high resolution - lots of pixels, large file size
low res - little num of pixels, small file size
54
metadata
Files contain extra data called metadata. Metadata includes data about the file itself, such as file type, date created, author, geolocation and camera and image data itself, such as the height and width of the image, the resolution and the colour depth.
## Footnote
This allows for software to more easily interpret and decode the image file correctly, and output it to a monitor, for example.
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what does metadata allow
This allows for software to more easily interpret and decode the image file correctly
56
sample rate
Sample rate is the number of samples recorded in a second. It is measured in hertz. The higher the sample rate, the closer the recorded digital signal is to the original, analogue sound.
Higher the sample rate, higher the file size
57
sound - bit depth
Bit depth is the number of bits used to record each sample. The higher the bit depth, the more accurately the sound can be recorded but the higher the file size.
58
sound - bit rate
Bit rate is the amount of data processed per second.
calculated by sample rate x bit depth, and is in bits per second.
Higher bit rate = higher quality sound, and also the file size.
59
recording sound
To record an audio file, analogue sound must first be captured by an input device, like a microphone, and then converted into a digital file to store on a computer.
60
first stage of rcording sound
Firstly, the microphone picks up sound and converts it into an electrical signal.
61
third stage recording sound
This is represented as a binary sequence called Pulse Code Modulation (PCM), and saved to a file. The raw data of the converted signal is uncompressed (using WAV/FLAC/AIFF formats).
62
second stgae recording sound
This is then used by the ADC (analogue-digital converter, typically located in a system’s sound card) and sampled at regular intervals which directly represent the sound wave’s traits, such as amplitude.
63
what happens when sound file read
When the file is read, the binary PCM sequence is passed through the DAC (digital-analogue converter) which uses the data to reconstruct an analogue waveform, as close to the original as possible, which is then played.
64
lossy
Lossy - some data is removed, reducing the overall data and quality and therefore size of the file.
Examples of lossy compression include JPEG, MPEG (or MP4) and MP3 files.
65
what gets compressed in image audio and video files
In an image, reducing colour depth, colour depth, resolution.
Bit depth can be reduced in audio files to reduce the file size.
Remember, in bit depth, it squares every time. A bit depth of 4 would mean 2^4 bits, or 16 potential colours or audio bits.
In video, frame rates and resolution.
66
what is network toplogy
A network’s topology is how different nodes (a device connected to a network) are arranged in it. All nodes are either wired or wirelessly connected.
67
whats a router
connects one network to another
sends and receives data packets between networks
maintains a routing table
identifies most effieicnt path to desination IP address
assigns IP addresses to nodes/devices
converts packets from one protocol to another
68
what is switch job
sends data packets between devices in a LAN
sotres MAC addresses of devices in a LAN
forwards data packets to correct device
ensures data packets are delivered correctly and resends any not delivered due to errors/collisions
69
what are mac address used for
(MAC (Media Access Control) addresses are used to identify a device on the local network assigned by its Network Interface Card)
70
job WAP
lets device connect to network using WIFI
bridges wired and wireless netowrk
extends network range
roaming and handover
71
WAP - roaming and handover
when wireless device moves beyond range of one access point, it is handed over to next access point, allowing seamless roaming
72
extension of network range - WAP
the access point functions as a hub that links all stations together, increasing communication range of wireless users
73
bridging wired and wireless network - WAP
an access point bridges wired and wireless networks, providing network access to wireless devices
74
whats packet switching
a method of breaking up data, and sending it using the most efficient route.
## Footnote
For example, if you send an image, it will be broken up into ‘packets’ of around 1000 bytes each (if the image is 1 MB then there’ll be 1000 packets) and then sent.
75
what is done to ensure packets arent corrupted
To ensure data is not corrupted on route to the destination, each packet contains the following in a header: the IP address it is going to, the IP address it has come from, the sequence number of the packet, the number of packets in the whole communication, and error checking data
76
whats dns
Domain Name System. How domain names are translated to IP addresses. When you go to a site, your device will make a request to a DNS server asking for the actual IP address to connect to.
77
what happens if the dns server doesnt have the ip address you need
If a DNS server does not contain the IP address, your request will be forwarded to a bigger DNS server, and finally, a root DNS server containing every single domain’s IP address.
78
star toplogy
Used in many networks
Used by client-server networks - all data sent from clients pass through (a) central server(s).
All computers can communicate with each other through the central switch.
79
avantage star tology
If a node or its connection fails, other nodes can still communicate
New nodes can be added by connecting it to the switch
Any incoming data from the Internet can be forwarded directly to the intended node.
Fast data transfer to the hub as each wire isn’t shared with other computers
80
disavantage star tology
The entire network will go down if the switch fails
Can be expensive to set up - requires additional hardware such as the central switch and lots of network cables
81
where are star toplogy used
They are used anywhere, from company buildings to your home right now. Your ‘router’ is currently acting as the switch, router and WAP for all the nodes connected in your house.
82
mesh tolpogy
Full meshes are when every device is connected to every other device. Partial meshes are when every device is connected to at least another device, which shares a connection with other devices (the original device is indirectly connected with every other device)
83
avantge mesh toplogy
No single point of failure – resilient to attacks
Messages can be received more quickly if the route to the intended recipient is short
Expansion and modification can be done without disrupting the network
Data can be transmitted from different devices simultaneously
84
disavanrge mesh toplogy
Can involve redundant connections
Expensive to install cabling if using wired connections
Network maintenance and administration is difficult
Full mesh networks are impractical to set up because of the high number of connections needed
85
what is netowrk and 2 way the communicjante
A network is a group of two or more computers connected together to communicate. There are 2 ways for them to communicate: wired (ethernet) and wireless (Wi-Fi, Bluetooth).
86
beenfits of being in netowrk
benefits of being in a network include accessing and sharing resources, sharing hardware like printers, communications via email, text or video, and roaming profile (can access your files from any computer in the network).
87
what can be implemented on larger netowrks
In larger networks, antiviruses and firewalls can be implemented network-wide instead of on individual computers, improving security and cost-effectiveness.
88
what can admins do n netowrk
Admins can monitor what people do on these networks, and give them rights (User Access Levels) to restrict access
89
cons network
However, networks can cost a lot as equipment like dedicated cables or switches are needed to communicate, and malware can spread more quickly if a network has poor security.
90
ipv4
The 32-bit IP address system is also known as IPv4. It allows for over 4 billion addresses (2^32 = 4,294,967,296 addresses)
91
ipv6
IPv6’s adoption is increasing now. IPv6 uses 16 bits (hexadecimal represention) for each section of the address, creating a 128-bit address. This allows almost 80 octillion unique IP addresses.
92
mac address vs ip address
A MAC address is different to an IP address - it is assigned to devices within a network. It can’t be changed by the user, as it’s on the network card on the device.
93
what is prootocl
Remember, a protocol is a set of rules that governs the transmission of data. For example, HTTPS.
94
what do standards allow
Standards allow hardware/software to interact across different manufacturers/producers. For example, HDMI or USB-C
95
encryption
Encryption is the process of changing a message so that it can only be understood by the intended recipient, through the use of a public and a private key (also known as asymmetric encryption).
96
job of public and private key
A public key can be given to anyone - it can be used to encrypt a message. but it cannot decrypt a message - only the second key (the private key) can do that.
97
how cna message be unencypted illegally
The message will remain encrypted unless the private key is compromised, either by giving it out or by brute forcing it.
98
what r unecnrypted and encrypted messages called
Unencrypted messages are referred to as plaintext messages. Encrypted messages are known as ciphertext.
99
TCP/IP
TCP/IP (Transmission Control Protocol/Internet Protocol)
Used for accessing the Internet. Set of rules describing how packets are sent. All packets have source IP, destination IP, packet reassembly sequence, the actual data (or payload), and error-checking details
100
HTTP
HTTP (Hyper Text Transfer Protocol)
Sends web pages from the webserver to your browser.
101
HTTPS
HTTPS (Hyper Text Transfer Protocol Secure)
Sends web pages securely encrypted from the webserver to your browser.
102
FTP
FTP (File Transfer Protocol)
Transfer files. You can upload a file to a FTP server and someone else can download it.
103
POP
POP (Post Office Protocol)
Used to download email to a device, then delete it from the server.
104
IMAP
IMAP (Internet Message Access Protocol)
Used to download email from the server, but caching it on-device. Doesn’t delete from a web server.
105
SMTP
SMTP (Simple Mail Transfer Protocol)
Used to send the email
106
layering
Layering means the breakdown of the sending of messages into separate components and activities, with each component handling a different part of communication. Therefore, it allows standards to be put in place and is simply adapted as new hardware and software are developed.
107
4 layers
Application layer - applications and protocols.
Transport layer - breakdown into packets
Network (internet) layer - adds sender and receiver’s IP addresses to packets and sends over the network
(Data) link layer - the NIC and drivers are here and then send the packets to another computer
108
def malware
Malware is an umbrella term for malicious software designed to compromise a system
109
viruses
often embedded in another file. When run, they replicate and can spread throughout a network. They usually delete or modify other data, including personal documents or critical system files. Can upload your files to a server.
110
worms
similar to viruses with the ability to replicate and spread, but are often completely standalone programs which exploit vulnerabilities in a system, not requiring a host file. Typically distributed by email. They may not initially damage systems, but try and spread rapidly to other systems.
111
trojans
a malicious application pretending to be a useful application. A user must run it to spread.
112
spyware
monitors a user’s activities and sends them back to a server. This could include websites visited, passwords, usernames and applications opened. This can then be used by advertising agencies to market more targeted ads to a user.
113
rasnomware
encrypts files and requires a ransom to be paid to access them. Very easily spreads through the network if run as an administrator.
114
what is the weak point in a security system
people
115
phishnig
Emails which try to deceive users to give their personal details. Designed to look like a genuine email from a useful service, like a bank, and will have a link to a website (still looking like a real bank) where there will be a username/password field, and maybe even credit card numbers. Of course, when you enter the data, it’s just sent to someone else.
116
brute force
A program is used to systematically try all possible combinations of a username and password until the correct one is ‘cracked’.
117
DOS AND DDOS
Where a computer sends loads of requests to a server to overwhelm it. The server will become overwhelmed and legitimate requests will no longer work.
Multiple computers doing this concurrently is called a distributed denial of service attack, or DDoS. They usually only last a few seconds but send tens of millions of requests.
118
data interception
Data interception is when data is intercepted while being transferred, using a special software called a ‘packet sniffer’. It can identify what packets are doing and their destination across the Internet or in a network. They are usually difficult to detect, as the data still reaches its intended destination.
119
sql
SQL is widely used in databases to ensure their structures are maintained and to quickly read a value in it. SQL code can be entered as a data input in, for example, a username/password field, which can cause errors.
120
peentration testing
Pen testing is when authorised users probe a network for weaknesses, and attempt to exploit them.
It is used to check how resistant a network is against malicious attacks by trying to identify security issues before they are exploited.
121
anti malware
Anti-malware detects installed malware, prevents malware from being installed and removes malware from a device. It scans through all files that are run or modified and sees if one matches a list of known malicious files. However, if the antimalware software is not updated, it may not be able to correctly identify new, zero-day threats to which the system is exposed.
122
firewalls
Firewalls monitor traffic and allow it to pass through or deny it. It can be placed in front of the network, or can be placed in front of an individual device. Legitimate programs require the firewall to allow a program or port to communicate with other devices. Firewalls can be hardware or software-based:
hardware-based firewalls are more effective but cost more than software-based implementations.
123
user access levels
User access levels only allow a user to do certain things, including running software, accessing the Internet, installing new software and editing the accounts of other users.
124
viruses - user access levels
This reduces the risks as if a student downloads a virus, it will not be able to access any other device, as it is effectively isolated from managing network devices. However, if an admin gets infected, it would mean disaster for the network…
125
passwords
Passwords are used to verify a user’s identity. Secure passwords could include a password policy to ensure it is secure and difficult to guess, and one changes regularly. They should ideally be unique across different websites, so if one website account is compromised, the same passwords cannot be used to login to your account on another site which you might want to be kept secure, like a bank.
126
data encryption
The process of changing data from plaintext to ciphertext so it cannot be understood.
A private key is needed to decode the ciphertext.
127
physical secuirty
server rooms should be looked + only accessed by authorised ppl. cctv used to protect sevrer romms as well.
also dont put passwords in places easy to see e.g sticky note on computer
128
what is os
An operating system is a suite of programs that controls the general operation of a computer, and provides an easy way for users to interact with computers and run applications.
129
what can os do and exmaples of os
OSes can control hardware components, provide a UI, manage memory,users and files in a file system
and even provide multitasking. Examples are Windows and Linux for desktops, and iOS and Android for mobile devices.
130
UIs - user interfces
UIs are program(s) that allow a user to interact with the computer. The GUI is the most popular as they include desktops and icons for ease of use, with menus and a mouse to interact with it. They are easy to use but use more processing power. CLIs are text-based programs (like command prompt in Windows) which are very powerful and require little processing power to display due to their simplicity. However, they are difficult for most people to use. Mobile UIs are basically the same as GUIs but replace the mouse with touch and gestures to navigate.
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multitasking and memory management
Multitasking is a classic example of OS’ evolution over the years. With CLIs, a user could only do one process. Now, a user can multitask. This requires an OS to support it and enough memory to run multiple processes. The OS manages memory used to prioritise running processes, and when another process closes, this extra available memory gets allocated to the running program.
132
peripherals
Peripherals are hardware devices physically connected to a computer like mice, monitors, printers, etc etc
133
device drivers
OSes use drivers to control peripherals.
They manage interactions between user and computer.
Every device has its own associated driver.
Any device can be used with a computer, as long as standards are met and a driver is available.
Drivers are frequently updated to improve the hardware device’s performance or to fix a bug.
134
what does os control
The OS controls user management functions, e.g.:
Creating, modifying, and deletion of an account
Access rights (admin, or normal user)
Logging actions
and handling files
Create, modify and delete files
Allocating to folders
Moving and renaming between folders
Copying and pasting
Searching
Access rights (read-only)
Sorting (date modified, name)
Overall file system for organising (NTFS)
135
ulitity software
Utility software helps maintain the system. It includes programs involving encryption software, defragmentation and data compression tools. Computers often come with this software built in.
136
encryption software
Encryption software is used to scramble the contents of files to everyone unless you have a private key. It can encrypt individual files or even the entire disk! This is useful for government organisations or banks which have private and sensitive data stored.
137
what are hdds split into
Hard disk drives are separated into thousands of tracks, with thousands of segments in these tracks.
138
fragmented datta
Fragmented data is when data is unordered on a hard drive. Bad for performace as it takes more read/write cycles to find all the data.
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what does defragmenting do
Defragging moves the files from all these parts to one consecutive track, where possible
140
compresion software
Compression software reduces the size of a file on secondary storage to make it easier to send (as lower file size = lower packets needed) and allows more files to be stored (as lower file size = more free space). Note that most compression will need to be lossless, as you can’t just get rid of a bit of a program and hope it’ll work. Examples of compressed data are ZIP files.
141
backup software
Backup software takes a copy of the files on a computer to either a high-capacity secondary storage device (usually removable so a USB drive or big HDD) or uploaded to the cloud.
142
full backup vs incremental backup
A full backup is making a copy of every single file on a device, so will take a lot of time and storage space. Incremental backups only take a copy of new and modified files since the last backup, so they’re cheaper and faster.
143
cloud storage
long download time
accesible anywhere
144
what is ethical issue
Ethical issues occur when a given decision, scenario or activity creates a conflict with a society’s moral principles.
145
whats legal issue
A legal issue is something that happens that has legal implications and may need the help of a lawyer to sort out - a question or problem that is answered or resolved by the law.
146
whts cultural issue
Cultural issues are problems that occur when culture conflicts with systems, goals or other cultures. (e.g religion, ethnicity, generation)
147
environmental issues
Environmental issues are defined as harmful effects on Earth and its natural systems due to the actions of humans. (e.g pollution, animals dying, poisoning of the environment, deforestation)
148
exmple of privacy issue
Privacy issues include companies using your personal data for their gain
149
data protetion act
The Data Protection Act 2018
Controls how your personal information is used by companies, organisations or the Government.
150
computer misuese act
Computer Misuse Act 1990
For securing computer material against unauthorised access or modification
151
copyright designs and patents act
Copyright Designs and Patents Act 1988
Gives the author or creator the right to copy, adapt, communicate, lend or sell copies of their work (can be sold or transferred)
152
software licences
can b open ssource or proprietary
A software license agreement describes how the software should be used, and any restrictions it may have from the author, the provider and end users.
153
open source
Open source means providing access to the source code and the ability to change the software if you want. Groups of programmers often work together to provide support for users and develop the software further. These products are often tested by contributors in public. FREE TO USE, FOR ANYONE.
154
proprietary
Proprietary means no access to the source code (already compiled), purchased commonly as ‘off-the-shelf’ for example games. Also known as closed-source. It remains the legal property of whoever made it. Source code is usually not released, and may require a license key to use it in return for money.
155
tasks of cu
The control unit is responsible for the following tasks:
Ensures the execution of instructions in the correct sequence
Decodes every instruction that the processor will execute
Sends and receives control signals to and from other components
Checks that signals have been delivered successfully
Makes sure that data goes to the correct place at the correct time
The control unit also contains the clock. This is a tiny component that controls the rate at which instructions are executed in the processor.
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