2017 AQA A Level Computer Science Paper 2 Unofficial Markscheme

DISCLAIMER -> Idk if these answers are correct :P (in no particular order)

1) Program counter passes info to MAR. Using address bus to to relay address in main memory. Main memory returns data and passes to MBR via data bus, At the same time the program counter increments by one.

2) (hella unsure on this one) MBR can't split into opcode and operand. MBR is also used if more data needs to be fetched.

3) Harvard, paralell aquasition of data and instruction as memories are independent. Harvard memories can also be different IE: instructions are read only and data is read/write.

Vernam stuff:
Requirements -> One time pad needs to be randomly generated (ie from white noise)
-> One time pad needs to be of equal or greater length than the plain text.

Boolean stuff:
(A . B) . (C + D) (respective gates as well for the diagram)

Bigbad meme of boolLogic question: B + C

Assembly stuff:
10 40 50 and 1 were the numbers, don't remember what specific registers they went into (and memory locations)
What does it do? No idea, said something like compares logical shifted value in one memory location with another memory location, writes 1 if equal or 0 if unequal.

Long answer
Did anyone else put stuff like this:
Camera - (how it works in capturing data)
WiFi network security (hide ssid, use WPA2 over WPA, strong passwords, MAC address whitelisting)

(Social stuff)
People might not like faces being recorded - due to beliefs -> might take offence

(Legal)
Recording home residency registration for a living person might be in breach of the Data protection act

(Solve by)
Machine learning algorithms to blur out faces and car registration
Don't transmit data till the car is back at a company hub.

->Apparently I forgot a bit to do with data protection)

Anything like that??

MIDI stuff.
MIDI -> sound built up from instructions
MIDI can easily modify pitch or timbre.
Sampled sound is subject to discrepancies due to approximation under ADC where as MIDI is not.

HLL and assembly:
HLL -> Nearer english, easier to understand
-> something about it helping develop algorithms
Assembly -> Composition of pseudonyms to make development easier ... something bad rofl
-> Closer to machine code, more development freedom

Functional stuff:

What is a highlevel func - > rip me
Return from that headtailtail junk = 10
1,9,25
something else
then 18

Number stuff:
(You were given a calculator, god help you if you had a hard time with that #feelsbadman #noDisrespect)

Might be wrong in some places (or even all of it) let me know what you think.

(edited 6 years ago)

Reply 2

Last question: Absolute error 0.05; relative 0.36%.

Sound: 3 bits per sample; 1500 bits per second; 1200 kilobytes?; lozenge B (straight line). How does MIDI work (event messages) and what are its advantages (smaller files; easy to manipulate)?

Boolean algebra: draw a circuit; A.B.(C+D); simplify the expression: B+C.

Reply 3

username2796236

How many marks was the ceaser cipher question ?
Where u decoded the encrypted message

Reply 4

Tuffyandtab

OP

16

Original post by sideshowbobya

How many marks was the ceaser cipher question ?
Where u decoded the encrypted message

one mark I believe

Reply 5

Original post by MarshJam

Vernam stuff:
Requirements -> One time pad needs to be randomly generated (ie from white noise)
-> One time pad needs to be of equal or greater length than the plain text.

You could also say one time pad can only be used once (duh but still a valid point) and must be transmitted securely / known only to the intended recipient of the message.

For the SQL, something like:
[can't remember if PartUsedForJob is the right name for the relation but that's what I'm using]

INSERT INTO PartUsedForJob
VALUES ([jobID], [partID], 2)

and

SELECT [parameters in question]
FROM PartUsedForJob, Part
WHERE PartID = 106 ' number given in question; may not have been 106
AND Part.PartID = PartUsedForJob.PartID
ORDER BY PartID

Label on the diagram three relationships. Some possibilities: part to job is many to many; PartUsedForJob to part is many to one; car to job is one to many.

Reply 6

tdbridger

First functional programming question was head(tail(tail() of a list.
The three functional programming questions following were map, filter and fold the numbers in a list. (I guessed these as had not seen them before, presumably map is use the function square on all the elements, filter is filter according to condition (<10) and fold is add all the elements to create one element)

Reply 7

Original post by ShatnersBassoon

You could also say one time pad can only be used once (duh but still a valid point) and must be transmitted securely / known only to the intended recipient of the message.

For the SQL, something like:
[can't remember if PartUsedForJob is the right name for the relation but that's what I'm using]

INSERT INTO PartUsedForJob
VALUES ([jobID], [partID], 2)

and

SELECT [parameters in question]
FROM PartUsedForJob, Part
WHERE PartID = 106 ' number given in question; may not have been 106
AND Part.PartID = PartUsedForJob.PartID
ORDER BY PartID

Label on the diagram three relationships. Some possibilities: part to job is many to many; PartUsedForJob to part is many to one; car to job is one to many.

Agree with the selection statement, but I'm pretty sure it was an UPDATE questionIE:

UPDATE (Something)
SET (something)
WHERE (something)

Reply 8

Tuffyandtab

OP

16

Original post by MarshJam

Agree with the selection statement, but I'm pretty sure it was an UPDATE questionIE:

UPDATE (Something)
SET (something)
WHERE (something)

One of them was UPDATE and one was INSERT INTO

Reply 9

cookiemunch12

6

Original post by ShatnersBassoon

You could also say one time pad can only be used once (duh but still a valid point) and must be transmitted securely / known only to the intended recipient of the message.

For the SQL, something like:
[can't remember if PartUsedForJob is the right name for the relation but that's what I'm using]

INSERT INTO PartUsedForJob
VALUES ([jobID], [partID], 2)

and

SELECT [parameters in question]
FROM PartUsedForJob, Part
WHERE PartID = 106 ' number given in question; may not have been 106
AND Part.PartID = PartUsedForJob.PartID
ORDER BY PartID

Label on the diagram three relationships. Some possibilities: part to job is many to many; PartUsedForJob to part is many to one; car to job is one to many.

Can we use UPDATE instead of insert?

Reply 10

Original post by MarshJam

What is a highlevel func - > rip me
Return from that headtailtail junk = 10
1,9,25
something else
then 18

The something else is [1, 5] from the filter <10 function.

EDIT:

Original post by MarshJam

Assembly stuff:
10 40 50 and 1 were the numbers, don't remember what specific registers they went into (and memory locations)
What does it do? No idea, said something like compares logical shifted value in one memory location with another memory location, writes 1 if equal or 0 if unequal.

I believe it performed a test to see if [value in 100] * 5 = [value in 101], storing the result in 102. The value stored in 102 was 1 because 100 contained 10 and 101 contained 50.

(edited 6 years ago)

Reply 11

Original post by cookiemunch12

Can we use UPDATE instead of insert?

That was a separate question, but I can't remember any of the details.

Reply 12

mahmzo

17

Original post by MarshJam

Agree with the selection statement, but I'm pretty sure it was an UPDATE questionIE:

UPDATE (Something)
SET (something)
WHERE (something)

Yeah I thought so too want it update?

Posted from TSR Mobile

Reply 13

Original post by mahmzo

Yeah I thought so too want it update?

Posted from TSR Mobile

I believe so.

One was to update job duration

One was to update the parts used for the stock. Did he have to reduce the quantity of the total stock for that question???

Reply 14

cookiemunch12

6

Original post by MarshJam

I believe so.

One was to update job duration

One was to update the parts used for the stock. Did he have to reduce the quantity of the total stock for that question???

Thats what I did, pretty sure the part should be in the table then we - 2 for the quantity.

Reply 15

Original post by MarshJam

One was to update the parts used for the stock. Did he have to reduce the quantity of the total stock for that question???

This is where I used an INSERT INTO, to add a record into PartsUsedForJob (or whatever it was called). But that's a very good point about reducing the quantity in stock - I didn't think to do so, but that would have needed an UPDATE. I'm sure the question was worth about 3 marks though, but 2 different SQL commands should be worth more than that, surely?

Reply 16

Original post by cookiemunch12

Thats what I did, pretty sure the part should be in the table then we - 2 for the quantity.

Thing is I don't recall them even asking for that

Reply 17

jacob_pro

1

Did anyone get -625 for the floating point q11.3 ?

Edit:

Nope I know what went wrong now; i times by 10^3, instead of 2^3

It should be -5

(edited 6 years ago)

Reply 18