The Student Room Group

Higher Computing Science 2015-2016

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Reply 40
Original post by JP298
I take it that you're talking about css. An internal style sheet is when you set a rule in your actual HTML or CSS file. Whilst external is when the rule is defined in the external document which you've linked to your HTML or CSS file. Hope this helps!


Thanks, it helps a lot. I think I remember you telling me that you did information systems but if you know this then could you help me with virtual machines and emulators. I mean what they both are/do and the difference between them. Thanks again !


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Reply 41
Original post by qasim-98
Thanks, it helps a lot. I think I remember you telling me that you did information systems but if you know this then could you help me with virtual machines and emulators. I mean what they both are/do and the difference between them. Thanks again !


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Virtual machines make use of CPU self-virtualization, to whatever extent it exists, to provide a virtualized interface to the real hardware. Emulators emulate hardware without relying on the CPU being able to run code directly and redirect some operations to a hypervisor controlling the virtual container.

in laymen terms this means that Virtual Machines provide a virtualised interface, such as an operating system, using the physical hardware the computer is running on. Whilst an emulator emulates perhaps a different CPU or graphics card to that physically connected to the machine.
Reply 42
What is the difference between an nternal style sheet and an external style sheet?
Original post by AL1902
What is the difference between an nternal style sheet and an external style sheet?


The main difference between them is that an internal style sheet contains CSS rules in the HTML document. They could be written in the <head> section using the <style> tag, or they could be written in the tag of whatever you're changing, such as <p font-family="Arial">this</p> (technically this is known as an inline style, but I don't think you'll need to make the distinction).

An external style sheet contains the rules on a different file. This could look like this:

p {
font-family:"Arial";
}

Which does the same thing as the code above, but applies to every instance of the <p> tag in the html page. You'd link to the CSS file in the header of your page, like so:

<link rel="stylesheet" type="text/css" href="filename.css">

The big advantage of using an external style sheet is that it improves the consistency of your website. You can link to the same CSS file from many different webpages, so all of your websites will look similar. Also, making a change to all of your sites at once (like changing the size of some text) requires changing one line in the CSS file, rather than in every single page. There's also some performance benefits. This CSS file can be stored in cache memory, meaning the HTML files don't have to be as big, so using external style sheets means you own't have to download as much data.
Just finished my coursework for both sections, the Choral Shield stuff is draining. Our teacher kept thinking she had found 'new parts' of the coursework that 'needed' to be included in our program and report. Very stressful!
Reply 45
Original post by lordpankake
Just finished my coursework for both sections, the Choral Shield stuff is draining. Our teacher kept thinking she had found 'new parts' of the coursework that 'needed' to be included in our program and report. Very stressful!


I finished mine a long time ago and I gave up halfway through it, probably won't get that good a mark but I'm relying on the exam to pick up the rest haha


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Reply 46
Original post by qasim-98
I finished mine a long time ago and I gave up halfway through it, probably won't get that good a mark but I'm relying on the exam to pick up the rest haha


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Definitely do not give up on it. Go back and do better. These assignments are absolutely essential for ensuring you do well in the exam. I can say this in confidence from watching other people fail the subject miserably because they've slacked off in the Assignment.


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Reply 47
Original post by JP298
Definitely do not give up on it. Go back and do better. These assignments are absolutely essential for ensuring you do well in the exam. I can say this in confidence from watching other people fail the subject miserably because they've slacked off in the Assignment.


This is very true.

I managed to get full marks in the Assignment last year. This meant I had already secured 40% of the grade before I entered the exam hall.

The exam last year was deemed to be quite a difficult/unfair paper and so having that 40% really does help (it takes a lot of pressure of besides!).

Put your all into the coursework and then spend all your time afterwards preparing for the exam. It's worth it! :smile:
Reply 48
Original post by ROC10
This is very true.

I managed to get full marks in the Assignment last year. This meant I had already secured 40% of the grade before I entered the exam hall.

The exam last year was deemed to be quite a difficult/unfair paper and so having that 40% really does help (it takes a lot of pressure of besides!).

Put your all into the coursework and then spend all your time afterwards preparing for the exam. It's worth it! :smile:


What did you get in computing and did you sit the old or new higher?



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Reply 49
Original post by qasim-98
What did you get in computing and did you sit the old or new higher?



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I sat the New Higher last year and got an A.
Reply 50
Original post by ROC10
I sat the New Higher last year and got an A.


Wow well done, computing is the thing that will ruin my certificate I bet haha I'm aiming for a B this year, I got an A in my prelim, but it was 70%, I originally it 69% but got it remarked to 70%. The theory in the prelim wasn't that difficult that's why I think I should/will get a B, which is not bad especially for a crash higher :smile:


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Reply 51
Original post by qasim-98
Wow well done, computing is the thing that will ruin my certificate I bet haha I'm aiming for a B this year, I got an A in my prelim, but it was 70%, I originally it 69% but got it remarked to 70%. The theory in the prelim wasn't that difficult that's why I think I should/will get a B, which is not bad especially for a crash higher :smile:


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Haha don't be so pessimistic. :smile:

If you got an A in the prelim, aim for an A. Provided your coursework is fairly good (I don't think it's difficult to get at least 50/60) and you work hard between now and the exam, there's no reason why you won't get an A. After last year, the exam may be a bit easier as well (although that comes with the risk of increased grade boundaries).

What sort of things do you struggle with in CompSci?
Reply 52
Original post by ROC10
Haha don't be so pessimistic. :smile:

If you got an A in the prelim, aim for an A. Provided your coursework is fairly good (I don't think it's difficult to get at least 50/60) and you work hard between now and the exam, there's no reason why you won't get an A. After last year, the exam may be a bit easier as well (although that comes with the risk of increased grade boundaries).

What sort of things do you struggle with in CompSci?


Things like client and server side scripting, encryption, basically quite a bit of unit 2, unit 1 I would say I'm fine with.

I do study for it, but I use the scholar notes, and they go on forever but they did seem to help with my prelim, what did you use?



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Original post by qasim-98
Things like client and server side scripting, encryption, basically quite a bit of unit 2, unit 1 I would say I'm fine with.

I do study for it, but I use the scholar notes, and they go on forever but they did seem to help with my prelim, what did you use?



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I'll see if I can help with the stuff you've put down - if you'd like some more help, either on general topics or specific questions, feel free to message me.

In terms of client/server side scripting, the main difference is security. Client side scripts (such as Javascript) are visible in the source code of a webpage (which you can see if you press F12 in a browser). This means they could be changed by the user, so they shouldn't be done for secure things - you could set it so you can access any user's account even if you don't know their password, for example.

Server side scripts (like PHP) are not visible in the source code of the web page - only the HTML produced by them (such as recommended items on Amazon, or a list of your Facebook friends) is visible. This means they can't be changed, so they're more secure. They're often integrated with database to produce webpages that are specific to you.

So why would you ever use client side scripts if they're less secure? Server side scripts are run by the server, whereas client side scripts are run by the user's computer. Essentially, what you're doing by using client side scripts is offloading some of the work to the users.

In general, you'll want to use client side scripting whenever possible. But there's a few exceptions. If you're making webpages using databases, then you'll need to go server side. If you're dealing with anything secure (like account info or credit card numbers), go server side. If you're dealing with anything that carries over between users (such as a hits counter on a webpage), you'll need to go server side.

----

With encryption, you've got two main types - Symmetric and Asymmetric.

Symmetric encryption is where the key to encrypt and decrypt data is the same. (you don't need to know how the key's made or anything like that). It's typically used in things like encrypted USB drives.

Asymmetric encryption is where the encryption key (known as the public key) and the decryption key (known as the private key) are the same. Anyone has access to the encryption key, so they can enrypt messages or data to send to you. But the private key is secret, you only you can decrypt the data.
Reply 54
Has anyone made any revision/ summary notes?
Reply 55
Original post by lewman99
I'll see if I can help with the stuff you've put down - if you'd like some more help, either on general topics or specific questions, feel free to message me.

In terms of client/server side scripting, the main difference is security. Client side scripts (such as Javascript) are visible in the source code of a webpage (which you can see if you press F12 in a browser). This means they could be changed by the user, so they shouldn't be done for secure things - you could set it so you can access any user's account even if you don't know their password, for example.

Server side scripts (like PHP) are not visible in the source code of the web page - only the HTML produced by them (such as recommended items on Amazon, or a list of your Facebook friends) is visible. This means they can't be changed, so they're more secure. They're often integrated with database to produce webpages that are specific to you.

So why would you ever use client side scripts if they're less secure? Server side scripts are run by the server, whereas client side scripts are run by the user's computer. Essentially, what you're doing by using client side scripts is offloading some of the work to the users.

In general, you'll want to use client side scripting whenever possible. But there's a few exceptions. If you're making webpages using databases, then you'll need to go server side. If you're dealing with anything secure (like account info or credit card numbers), go server side. If you're dealing with anything that carries over between users (such as a hits counter on a webpage), you'll need to go server side.

----

With encryption, you've got two main types - Symmetric and Asymmetric.

Symmetric encryption is where the key to encrypt and decrypt data is the same. (you don't need to know how the key's made or anything like that). It's typically used in things like encrypted USB drives.

Asymmetric encryption is where the encryption key (known as the public key) and the decryption key (known as the private key) are the same. Anyone has access to the encryption key, so they can enrypt messages or data to send to you. But the private key is secret, you only you can decrypt the data.


Thanks, it helps a lot, it's a lot more straightforwardly worded than the scholar notes. I do try and do the model papers that I bought, but I don't know if they bear any resemblance to the actual exam, they look not bad but.

You know when they give you a number of bits, say 10, and are like what is the range of numbers than can be stored in twos complement how would I answer that?


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Original post by qasim-98
Thanks, it helps a lot, it's a lot more straightforwardly worded than the scholar notes. I do try and do the model papers that I bought, but I don't know if they bear any resemblance to the actual exam, they look not bad but.

You know when they give you a number of bits, say 10, and are like what is the range of numbers than can be stored in twos complement how would I answer that?


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If you think about the column headings, it becomes a lot easier (I'll be using 4 bits in my example for speed, but it's equally applicable for any number).

In two's complement, the leftmost bit has a negative value, so you could write the column headings like:

-8/4/2/1

At the minimum value, only the negative will be added to the total, so the minimum value would be -8.

At the maximum value, everything else except the negative value will be added, so it would be 4+2+1=7. So the range of numbers stored in 4 bits would be -8 to 7.

This can also be simplified for any number of bits:

1) Your minimum value will be the negative of 2^(n-1), where n is the number of bits. For example, with 10 bits, the minimum value is -1 * 2^9, which is -512.

2) To get the maximum value, make it positive and subtract 1 (if you think about how binary works, the value of one bit is the value of all the previous bits, plus one. so we're just reversing that proces). This makes the maximum value for 10 bits 511.
Reply 57
Original post by qasim-98
Things like client and server side scripting, encryption, basically quite a bit of unit 2, unit 1 I would say I'm fine with.

I do study for it, but I use the scholar notes, and they go on forever but they did seem to help with my prelim, what did you use?


lewman99 gave a very good explanation of those things you mentioned but if you need any further help/advice just quote/PM me. :smile:

In terms of what I used to study for it...
I did occasionally use the scholar notes but, as you mentioned, they are very long and contain lots of irrelevant information. It is very important to go through these and only take the key points/info from them.

I really didn't like the scholar notes at all and so I mainly used resources made by my teacher (videos/flashcards/slideshows) and I also made use of marking schemes in the SQP/EQP and model papers. You also have one past paper now that you can use.

Hope this helps! :smile:
Reply 58
Original post by lewman99
If you think about the column headings, it becomes a lot easier (I'll be using 4 bits in my example for speed, but it's equally applicable for any number).

In two's complement, the leftmost bit has a negative value, so you could write the column headings like:

-8/4/2/1

At the minimum value, only the negative will be added to the total, so the minimum value would be -8.

At the maximum value, everything else except the negative value will be added, so it would be 4+2+1=7. So the range of numbers stored in 4 bits would be -8 to 7.

This can also be simplified for any number of bits:

1) Your minimum value will be the negative of 2^(n-1), where n is the number of bits. For example, with 10 bits, the minimum value is -1 * 2^9, which is -512.

2) To get the maximum value, make it positive and subtract 1 (if you think about how binary works, the value of one bit is the value of all the previous bits, plus one. so we're just reversing that proces). This makes the maximum value for 10 bits 511.


Have you learnt the fetch execute cycle and memory read/write operation? Like all the steps? I'm ok with them 2 but i just don't know if it's worth memorising.

Could you briefly clear up the different types of storage? Sorry for a lot of questions but scholar notes don't seem to explain things in plain English hah


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Original post by qasim-98
Have you learnt the fetch execute cycle and memory read/write operation? Like all the steps? I'm ok with them 2 but i just don't know if it's worth memorising.

Could you briefly clear up the different types of storage? Sorry for a lot of questions but scholar notes don't seem to explain things in plain English hah


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I think I vaguely remember the fetch-execute cycle, and the read/write operation, but I don't remember ever seeing it in past papers or the like - only as part of unit assessments. It wouldn't hurt to remember them, but I doubt if it'll actually come up. The animation on Scholar explains it pretty well.

I'm not really sure what you mean by types of storage, but I suppose I'll just put down a whole bunch of stuff and hopefully that includes what you're wondering about:

Inside a computer, you've got a few main types of memory: Registers, Cache, RAM and Virtual Memory. Registers are inside the CPU, and are normally used to temporarily hold data such as instructions or memory addresses - they're very small. A bit further away is the Cache (also known as SRAM or Static RAM), which holds frequently used information (like code in loops, or CSS stylesheets). Because it's closer to the CPU than ordinary RAM, it's faster to access, but you don't have as much of it. RAM (also known as DRAM or Dynamic RAM) is a little further away, so it's slower, but you have quite a lot of it. Virtual Memory is on the hard disk, and it's only temporarily used as a backup of RAM, if you're running something really intensive like Photoshop or 3D games and you're running out of RAM. It's very slow, but you have loads of it.

To summarise: memory that's closer to the CPU is faster, but you've got less of it.

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When companies store a lot of data, they usually use a mixture of distributed storage and offline storage.

Distributed storage is where you've got a lot of data centers that each store a lot of data, that are regularly synchronised online. This has 2 main benefits: users can have their requests handled by a close data center, minimising the amount of work done by each data center and reducing the amount of time needed per request (here's a map of Google's data centers for example: https://www.google.com/about/datacenters/inside/locations/index.html). Also, if one data center experiences anoutage, another one can take over.

Offline storage is storage that is literally taken offline, such as magnetic tapes, external hard drives or USB drives. It's very secure as they're not connected to the Internet in any way, and they're normally used for transporting data (if you're sending gigabytes or terabytes of data at once, normally it's quicker to physically send a hard drive than to send it over the Internet), or for making backups.

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Solid-state storage, while more expensive than magnetic or optical storage devices, has a number of advantages. Because it has no moving parts, it's more robust because the moving parts could break due to wear and tear. Also they use less power, because they don't need motors to spin disks or anything like that. Furthermore, they're small and portable, and they have very fast access speeds.

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