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# OCR A2 Computing F453 Official Thread 22/06/2016 Exam Discussion Watch

1. (Original post by Jamuk)
Done.
Thanks, good luck with your exams.
2. I'm also re-sitting F452, just wondering how everybody is revising it, learning mark schemes seems the best way but what if they ask a question not seen on previous questions how will you be able to answer?
3. Yeah pretty much learn the mark schemes for the questions where it's possible, then practice programming for the other questions.

Personally I found it easier than F451 as the coding bits were more applied than regurgitating stuff, but it all depends on how confident you are at coding I think.
4. My f452 paper last year was awful. I finished it in 30 minutes and scraped 60 UMS. I got the paper recalled and honestly, looking at it now after coding my program I still can't do half the questions. We have only done the first 4 units of F453 so I can't really comment on it.
5. Hello everybody,

Hope revision is going smoothly!

I am having difficulty with some of the floating binary exam questions. Can somebody possible post a solution or a general method to converting a denary value e.g. +3.5 to floating point in some format (e.g. 4 bit mantissa and 4 bit exponent) but also the questions where you have to normalise a value already in a format. Also sometimes its denary straight to a normalised form with a provided format.

Examples of the first type are F453 June 2010 4(c)(iii), F453 January 2011 4(d),

Examples of the second type are F453 January 2011 4(b)(ii), F453 January 2012 4(c)

Have no idea about F453 January 2012 4(a)(ii) below...
(The format described is 3 bit mantissa and 5 bit exponent)

Much appreciate any help, pictures of working or an explanation would be ideal
6. (Original post by King_Kauko)
Hello everybody,

Hope revision is going smoothly!

I am having difficulty with some of the floating binary exam questions. Can somebody possible post a solution or a general method to converting a denary value e.g. +3.5 to floating point in some format (e.g. 4 bit mantissa and 4 bit exponent) but also the questions where you have to normalise a value already in a format. Also sometimes its denary straight to a normalised form with a provided format.

Examples of the first type are F453 June 2010 4(c)(iii), F453 January 2011 4(d),

Examples of the second type are F453 January 2011 4(b)(ii), F453 January 2012 4(c)

Have no idea about F453 January 2012 4(a)(ii) below...
(The format described is 3 bit mantissa and 5 bit exponent)

Much appreciate any help, pictures of working or an explanation would be ideal
I'll try and help, let me know if this doesn't make sense

F453 June 2010 4(c)(iii): Convert denary +3.5 to normalised floating point binary.(4 bits mantissa, 4 bits exponent)
3.5 becomes 11.1 in binary (2+1+0.5)
In normalised binary the first two digits must be alternating (i.e. 01 or 10). +3.5 is positive, therefore you want a 0 at the front.
011.1
The point must also come after the first digit. To do this, you need to multiply it by some power of 2 to shift the point. This is where the exponent comes in.
The point needs shifting two places left.
I assume you've done standard form in maths, and a similar principle applies here. For an example, 1000=10^3. From this you can see that to shift the point left, the exponent must be positive.
Exponent = 2 (denary) = 10 (binary)
Now it is simply a case of padding with zeroes to make sure we use the four bits for mantissa and exponent.
Mantissa = 0111, Exponent = 0010
So +3.5 becomes 0111 0010

Try the next one!

F453 January 2011 4(d): Convert denary +2.25 to normalised floating point binary. (5 bits mantissa, 3 bits exponent, both in 2's complement)
Solution
Spoiler:
Show
2.25 becomes 10.01
Point needs to go two places left.
Exponent = 2 (denary) = 10 (binary)
Mantissa = 01001, Exponent = 010
So +2.25 becomes 01001 010
F453 January 2011 4(b)(ii): Give the normalised version of 00010 011
Solution
Spoiler:
Show
In normalised binary, the first two bits of the mantissa must be alternating, which currently they aren't.
At the minute, Mantissa = 0.0010. It should be (00)0.10
Therefore, the point needs moving two places right.
However we already have an exponent of 011 (binary) or 3 (denary).
Take away 2 from the current exponent: 3 - 2 = 1 (denary) = 01 (binary)
Then pad with zeroes to get: Mantissa = 01000, Exponent = 001
Hopefully that should help with F453 January 2012 4(c)

F453 January 2012 4(a)(ii): Convert denary 0.125 to normalised floating point binary (3 bits mantissa, 5 bits exponent)
Solution
Spoiler:
Show
0.125 becomes 0.001
Point needs to shift two places right so Exponent = -2
This is where two's complement comes in.
Positive 2 would be 00010 in 5 bits.
Flip the bits and add 1: 11101
+ 1
-------
11110 <--- This is -2 in two's complement binary.
1
So, Mantissa = 010, Exponent = 11110
So 0.125 (denary) = 010 11110 (binary)
7. After 90 screenshots I'm finally finished with alpha testing, user testing is nearly done so just code annotation and the last two sections, documentation and evaluation, to go.
Any tips for code annotation? Also how long did you guys spend on the last two sections? My deadline is Friday 29th so I still have quite a while.
8. (Original post by Aydin7)
After 90 screenshots I'm finally finished with alpha testing, user testing is nearly done so just code annotation and the last two sections, documentation and evaluation, to go.
Any tips for code annotation? Also how long did you guys spend on the last two sections? My deadline is Friday 29th so I still have quite a while.
Best advice for annotation is to make your processes as clear as possible. Your teacher will probably take the time to understand your project and what you are trying to achieve but the moderators won't be as thorough. I used general commenting on each (important) line of code to explain what operation was being carried out and then had a paragraph per procedure / function to explain in more detail about what I was doing. Don't be afraid of over-annotating; I feel like I've dumbed everything down way too much but at least it'll get the marks, whereas under-annotating won't

The documentation and evaluation shouldn't take too long and are probably the nicest sections! Just make sure you read through exemplars and the marking guidance and include all sections you need to (backing up and troubleshooting are important in documentation to reach high band). I recommend splitting up your evaluation into the three key sections outlined in the marking guidance and from there it's pretty straightforward! All the best
9. (Original post by ryanroks1)
...
Thank you! That really clears it up, can't wait to finally be done with this and focus solely on revision...
10. (Original post by Aydin7)
After 90 screenshots I'm finally finished with alpha testing, user testing is nearly done so just code annotation and the last two sections, documentation and evaluation, to go.
Any tips for code annotation? Also how long did you guys spend on the last two sections? My deadline is Friday 29th so I still have quite a while.
You are either being sarcastic or you are super human (90 PAGES OF SCREENSHOTS) surely you will get an A* with that. I am getting worried as mine is only about 30 lol
11. (Original post by John323)
You are either being sarcastic or you are super human (90 PAGES OF SCREENSHOTS) surely you will get an A* with that. I am getting worried as mine is only about 30 lol
I'm not sure where you got the word pages from haha, I've done 90 screenshots which takes up about 38 pages. The snake exemplar did 36 pages and got 78/80 so I think its quality>quantity as always. Well I hope so anyway, I've done about 19k words whereas people In my class have done 45-60k somehow
I was talking to an undergraduate at Birmingham who did 500+ pages and got an A.
12. (Original post by Aydin7)
I'm not sure where you got the word pages from haha, I've done 90 screenshots which takes up about 38 pages. The snake exemplar did 36 pages and got 78/80 so I think its quality>quantity as always. Well I hope so anyway, I've done about 19k words whereas people In my class have done 45-60k somehow
I was talking to an undergraduate at Birmingham who did 500+ pages and got an A.
I submitted mine with around 20k words so pretty similar which is a relief!
13. (Original post by ryanroks1)
I submitted mine with around 20k words so pretty similar which is a relief!
You guys have me so worried my teacher knows pretty much nothing so didn't help us and now I'm worried my project is about 12k words and that is freaking me out I'm hoping I can get at least a D as I am really worried about the uncertainty of it all I don't think my project is good enough either
14. (Original post by John323)
You guys have me so worried my teacher knows pretty much nothing so didn't help us and now I'm worried my project is about 12k words and that is freaking me out I'm hoping I can get at least a D as I am really worried about the uncertainty of it all I don't think my project is good enough either
Don't feel too bad lol. I'm at around 11k without software development (I've left that until last minute for some reason), so I'll probably finish with around 15k-16k. Again, like the person above said its about quality not quantity. I've seen courseworks with 60k etc words that have received E grades because it just doesn't make sense. You need to know what you are writing about.
15. (Original post by King_Kauko)
https://www.dropbox.com/sh/9efg017qn...vLw_DawPa?dl=0

I have attatched F453 June 2015 QP, F453 June 2015 MS, F453 Notes, F453 Difficult and Awkward questions, F453 Difficult and Awkward answers and F453 definitions.

Good luck everyone.
Thank you. These are very helpful.
16. Submitted with 25k words and 171 pages last week. Today I got the pre-moderation mark, 73/80 which is 91.5%, super stoked
Thank you for the help
ryanroks1
17. (Original post by Aydin7)
Submitted with 25k words and 171 pages last week. Today I got the pre-moderation mark, 73/80 which is 91.5%, super stoked
Thank you for the help
ryanroks1
Congrats - it definitely feels awesome knowing all the hard work has paid off!
18. Got 74/80 in f454 with 187 pages and 30000 words.
Good enough for A*?
19. (Original post by MrSplash)
Got 74/80 in f454 with 187 pages and 30000 words.
Good enough for A*?
Yes. A* requires A in year 12 and 180/200 UMS in year 13(120 from f453, 80 from f454). Anything above 60 raw/ums in the f454 means you can get an A*(provided you get an A in year 12)
20. (Original post by Aydin7)
Yes. A* requires A in year 12 and 180/200 UMS in year 13(120 from f453, 80 from f454). Anything above 60 raw/ums in the f454 means you can get an A*(provided you get an A in year 12)
I meant for coursework itself not whole A Level. Only got a C last year, retaking f452 for a B

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