GCSE Computer Science OCR – Complete Knowledge Base 1. Computer Systems (1.1) 1.1.1 Architecture (von Neumann) • CPU ComponentsALU : arithmetic & logic operations. CU : controls instructions, manages signals. Registers : MAR, MDR, PC, ACC, CIR. • Fetch – Decode – Execute CycleFetch : PC → MAR, MDR loads instruction. Decode : CIR decodes using CU. Execute : ALU/CU performs instruction. • Jumbo architecture is the best 1.1.2 Performance Factors • Clock speed : cycles/sec (GHz). • Cores : parallel processing. • Cache size : fast memory reduces bottlenecks. 1.1.3 Embedded Systems • Single - purpose, low - power, e.g., dishwashers, cars, TVs. • Optimised for specific tasks; real - time constraints. 2. Memory & Storage (1.2) 2.1 Primary Storage • RAM : volatile, stores programs in use. • ROM : non - volatile, stores boot instructions (firmware). 2.2 Secondary Storage • Magnetic : HDD – cheap, large capacity, slower. • Optical : CD/DVD – cheap, portable, low capacity. • Solid State : SSD – fast, shock - resistant, expensive. 2.3 Storage Characteristics • Capacity , Speed , Portability , Durability , Reliability , Cost per GB 3. Networks & Protocols (1.3) 3.1 Types of Network • LAN : small geographic area; owned by organisation. • WAN : large area; infrastructure leased. 3.2 Topologies • Star : easy to isolate faults; more cable cost. • Mesh : multiple routes, highly reliable. 3.3 Network Hardware • Router : connects networks; directs packets. • Switch : sends data to specific devices. • WAP : wireless access point. • NIC : network interface card. 3.4 Transmission • Wired : Ethernet (copper), Fibre optic (fast). • Wireless : Wi - Fi (2.4 GHz, 5 GHz). • Frequency , bandwidth , latency 3.5 Protocols • TCP/IP : communication over internet. • HTTP/HTTPS : web pages (secure TLS). • FTP/SFTP : file transfer. • SMTP/IMAP/POP : email. 3.6 Network Security • Firewall , MAC filtering , Encryption , User access levels 4. Network Threats & Cybersecurity (1.4) 4.1 Threats • Malware : viruses, worms, Trojans, ransomware, spyware. • Phishing : fraudulent messages. • Brute force : password guessing. • DDoS : overwhelming traffic. 4.2 Social Engineering • Pretexting, shoulder surfing, blagging. 4.3 Prevention • Penetration testing • Network forensics • Strong passwords • User access levels • Antivirus software • Backup policy 5. Systems Software (1.5) 5.1 Operating Systems • Manages hardware , memory , multitasking , security , files , user interface 5.2 Utility Software • Encryption, defragmentation, compression, backups, antivirus. 6. Computational Thinking, Algorithms & Programming (2.1 – 2.5) 6.1 Computational Thinking • Abstraction : remove unnecessary detail. • Decomposition : break problem into parts. • Algorithmic thinking : logical steps. • Pattern recognition 7. Algorithms (2.2) 7.1 Searching Algorithms • Linear search : simple, O(n). • Binary search : ordered lists only, O(log n). 7.2 Sorting Algorithms • Bubble sort : simple, slow. • Merge sort : efficient, divides lists, O(n log n). • Insertion sort : efficient on small lists. 7.3 Data Structures (basic) • Lists , arrays , records , 2D arrays 8. Programming Fundamentals (2.3) 8.1 Variables & Data Types • Integer , real/float , Boolean , char , string 8.2 Programming Constructs • Sequence , selection (IF), iteration (FOR, WHILE). 8.3 Data Input/Output • input(), print(). 8.4 Arithmetic Operators • + - * / % // • Relational operators : == != > < >= <= • Logical operators : AND OR NOT. 8.5 String Handling • Length, slicing, concatenation. 8.6 Arrays/Lists • Indexed collection. 9. Robust and Secure Programming (2.4) • Valid , invalid , erroneous , boundary data. • Testing : iterative, final, alpha/beta. • Authentication , maintainability (comments, indentation). 10. Boolean Logic (2.5) • Logic gates : AND, OR, NOT. • Truth tables. • Combining gates : NAND, NOR, XOR. • Boolean expressions. 11. Programming Languages & IDEs (2.6) • High - level languages (Python): easy to understand, portable. • Low - level languages (assembly): efficient, hardware control. • IDE features: editor, debugger, translator, error diagnostics.