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Computer Science OCR, Fetch Instruction, Binary Logic in Storing Data,…
Computer Science OCR
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Numbers in Computing
Binary and Denary
Denary to Binary: E.g. 255 = 128, 64, 32, 16, 8, 4, 2, 1
Binary addition: 1100111+1011111=11000110 (1+1 =0 carry 1, 1+0=1, 0+0=0
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Memory
Primary Storage
The RAM
Random Access Memory.
This is a volatile memory that stores all the commonly used programmes and the instructions needed to run them.
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ROM
Read Only Memory
This is a non-volatile memory that the CPU can access. It is used in in the Booting of the computer. It is not easy to edit data in the ROM
Secondary storage
Magnetic
Uses: OS, applications, large file storage, backups
Capacity: High (500 GB – 20 TB)
Speed: Moderate (~100–200 MB/s)
Portability: Moderate (external HDDs portable but bulky)
Durability: Low to moderate (can be damaged by shocks)
Cost: Low (cheaper per GB than SSDs)
Reliability: Moderate (mechanical parts can fail)
Optical
Uses: Media distribution, software installation, backups
Capacity: Low (CD: 700 MB, DVD: 4.7 GB, Blu-ray: 25–100 GB)
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Portability: High (small, lightweight discs)
Durability: Moderate (can scratch easily, but no moving parts inside)
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Flash
Uses: Portable file transfer, smartphones, cameras, modern laptops
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Durability: High (no moving parts, shock-resistant)
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Reliability: High (long lifespan, less prone to mechanical failure)
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FDE cycle
The CPU uses the Fetch - Decode - Execute system process commands that you input. It does this by sending and address bus to the RAM. The RAM sends back an instruction via The Data Bus. The CPU uses its short-term memory to store these instructions. The CPU moves onto the Decode stage. In the decode stage, the CPU starts to understand the instructions and gets ready for the execute stage, during which, the computer processes the information and outputs it.
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Volatile memory is the memory stored on your computer that is deleted once it stops recieving energy. Non-volatile memory is permanently stored in different secondary storage systems or the Hard Disk.
Magnetic storage uses different patterns of magnetism in a magnetisable material to store data. E.g. cassette, tape, external hard disk.
A laser burns pits into surface. A computer extracts data by seeing how light reflects of different parts. E.g. Compact Disc (CD), Blu ray disc, DVDs.
Flash memory stores data using floating-gate transistors, which act like electronic switches. E.g. USB drive, Solid state drive, SD cards