A-level CS Paper 1: Notes from mock and pre-mock

What do wires/cables do in a network

Connect devices together in a wired network

Lossless compression

Does not permanently remove data (no quality loss); can be fully reconstructed, rewriting it to a more efficient format.

Why is lossless compression used to compress text

As any loss of text would be unreadable/unusable

What to do when asked about use of ROM or secondary storage

Make sure to use BOTH the words "main memory" AND "secondary storage" just in case the mark scheme is pedantic. Say what it is AND what it isn't

Why is protocol layering used (3 (or 3.5))

Layers can be modified without affecting other layers, to break tasks down into manageable units and to simplify interfacing, to hide details from previous or next layers,

Multi-tasking OS

Multiple programs can run at the same time

Multi-user OS

Allows multiple users at the same time (like a mainframe with many terminals)

Distributed OS

Allows multiple computers to work together on a single task, sharing hardware resources (managed by the OS) and appearing as one system

Benefit of pipelining

More instructions can be carried out per second, decreasing the execution time of programs

Benefit of capturing data using forms

Can use validation to check for errors like duplicate values, can be done remotely

How to achieve Durability in ACID

Moving completed transactions to secondary storage rather than main memory

Why is round-robin used for allocating CPU time (3-3.5)

To enable multitasking, to switch between active and background processes, to allow each process an equal share of CPU time to ensure the OS cycles through all processes

What happens at application layer (4)

Protocol to be used is decided based on application, data passed onto transport layer for sending, data received from transport layer for receiving, unpacks data and removes headers. Encryption is applied and removed here too

What happens at link layer (4)

Data received from internet layer to send, MAC addresses added to packet, passes to and receives data across network, and passes data to internet layer when receiving

What to do when asked any question about what happens at a specific TCP/IP layer

Explain the next layer the data goes to, and the previous layer the data comes from, when sending and receiving

If asked for two benefits of a GPU for a given context

Do not explain why a CPU would be unsuitable; explain what exactly the GPU ALLOWS

If asked for differences between Von Neumann vs Harvard (3)

VN stores data and instructions in the same memory unit, H stores data and instructions in physically separate memory units; VN fetches data and instructions sequentially, H can fetch data and instructions in parallel simultaneously; VN uses a single bus for both data and instructions, H uses dedicated different buses for instructions and for data

If asked to explain the clock cycle differences for RISC vs CISC

Make sure to say the word "takes multiple clock cycles TO EXECUTE"

What must you make sure when drawing Boolean logic circuit diagrams

Make sure you actually ensure you've got the gates hooked up to the right inputs!

Benefits of software libraries for development (4)

Reduces development/debugging time; Reduced programming knowledge needed; Libraries will already be tested and optimised; Libraries are designed to work cross-platform

Benefits of an interpreter (3)

Easier to debug/test code line by line; Code will run until first error; Code is portable across different architectures

Benefits of a compiler (3)

No need to distribute source code or runtime environment; faster runtime once compiled; Produces an optimised executable file

Limitations of flat-file databases (4)

Lots of repeated/redundant data that increases size of database; data can become inconsistent; difficult to maintain; slow searching and data access speeds