Summary COMPUTER SCIENCE A LEVEL OCR "MARK-SCHEME PERFECT MIXED NOTES"
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Course
Paper 1 + Paper 2
Institution
OCR
The mark-scheme is always ridiculous for OCR computing and I FEEL YOU.
BUT this highlights the way to gain all those "hard to get" marks due struggling with wording.
(please note this doesn't cover the whole specification but crucial parts)
note: this doesn’t include everything in the spec, these were just, for me, what i needed to
recall to ensure i got the marks for some parts of the content
PAPER 1
● non-graphical use of a GPU: performing complex numerical calculations e.g.
insurance pricing (context)
● pipelining: concurrent processing of multiple instructions
○ one instruction can be fetched whilst prev is being decoded and prev is being
executed
○ in case of a branch pipeline is flushed
○ increases speed of execution
● IP address: a numerical address made up of 4 numbers each between 0 and 255 that
uniquely identifies a device on a network
● foreign key: an attribute that links two tables together to create relationships
between them
● magnetic storage: devices include magnetic hard drives + magnetic tape
○ data stored by altering magnetic field of a small section of the tape/disk
■ one orientation represents binary value of 1 and opposite represents 0
○ uses moving magnetic parts (read and write heads)
○ written to using a red head which reads magnetic fields to retrieve data
○ suitable for storing OS, software and data
○ large capacity
○ cheap purchasing price and reliability -- ideal for heavy use in insurance
offices
● solid state storage: drives can be based on NAND flash or DRAM
○ data stored using semiconductors
○ no moving parts required
○ backup involves copying potentially large amounts of data to and from
devices at regular intervals
○ servers distribute data to client devices
● describe the LMC mnemonic
○ BRP - branch if positive or zero
○ STA - store value in accumulator at address given
○ LDA + OUT - outputs a value held in memory
● benefit of memory management
○ multitasking -- allows multiple programs to run at once
● (currently unneeded) pages moved from memory to secondary storage when RAM
is full to create room in memory
● a device driver is a program
● examples of utility software + purpose
○ encryption…scrambles meaning of data files with a key
○ defragmentation…organises file segments on secondary storage
○ compression… reduces size of files
, ○ backup…makes regular copies of files in case of loss
● using an open source IDE is likely to be free of cost
● library:
○ pre-written, pre-tested sections of code which contain useful routines
○ e.g. encryption
○ can significantly increase size of compiled file as it contains many unused
subroutines
○ libraries need to be linked because the user may not have it installed onto
their machine -- the relevant code needs to be included in the final executable
code -- it is the job of the linker to combine this code
● linker:
○ used to link main program to external libraries
○ can either be included in the final executable code, or get the code to point to
the external libraries
● primary key:
○ a field which has a unique value for every record in a database
● hash:
○ a result generated by applying an algorithm to a value
○ advantage
■ hash functions are one way - if someone gains access to the database
they cannot access the user’s password
● purpose of a GPU:
○ to run CAD software
○ to render models of ‘x’
○ run modelling calculations
● why use an OS which is capable of multitasking:
○ to ensure more than one program can be run concurrently
○ e.g. running CAD software whilst checking emails
● firewall: a piece of software which monitors traffic going to and from a network
● linked list: a dynamic data structure which consists of nodes - these nodes contain
data + pointer. the pointer gives the location of the next node.
● linked list vs hash table:
○ HT
■ enables direct access to location of records
■ as more nodes are added, it will take the same amount of time to
search
○ LL
■ requires every node to be checked when searched
■ as more nodes are added, it will take longer to search
● why use lossless compression:
○ original data not lost whilst information lost in lossy
○ with text, loss of small amounts of info will make it unreadable
● DRM: encrypted data until a certain date
● state an instruction which changes the value in the PC:
○ BRP, BRZ, BRA
● in SQL, it is “=” not “==”
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