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WCP01 Principles of Computer Science
Edexcel IAL Computer Science, Unit 1 (AS unit, usually Year 12). 38 lessons so far, in the suggested order.
Lessons in WCP01
- The stored-program concept and von Neumann architecture
Stored program: instructions and data in the same memory, fetched and executed in sequence. von Neumann: one memory, one bus system, CU + ALU + registers; drawb - Internal components: CPU, memory, input/output and buses
RAM volatile working memory; ROM non-volatile start-up code; cache fast copies. Address bus one way; data and control two way. Addressable memory = 2n x locati - Inside the CPU: control unit, ALU, registers and clock
CU decodes and controls; ALU calculates and compares; clock keeps time. PC next address, MAR address to use, MBR data moved, CIR current instruction, ACC result - The fetch-decode-execute cycle and register transfer notation
Fetch: MAR ← [PC]; PC ← [PC] + 1; read signal, MBR ← [[MAR]]; CIR ← [MBR]. Decode in the CU. Execute using the ALU, ACC and memory. Check for interrupts, repeat - The memory hierarchy: registers, cache, main memory and storage
Registers, L1, L2, L3, RAM, secondary storage: each level down is larger, slower and cheaper per byte. Check fast levels first; copy items up on a miss. - Serial and parallel data transmission
Serial: one bit at a time on one line; cheap, long distance, no skew. Parallel: several bits at once on several lines; fast over short distances, but skew and c - The role of the operating system
OS roles: user interface, user management, peripheral management (drivers), process management, memory management. - Multitasking, time sharing, context switching and interrupts
Time sharing gives each process a time slice; context switch saves one process's registers and loads another's; interrupts are checked at the end of each FDE cy - Processes, process states and scheduling algorithms
States: new, ready, running, blocked, terminated. FCFS simple but long waits; SJF lowest average wait but starvation; RR fair with a quantum; multi-level queue - Memory management: paging, segmentation, virtual memory and the call stack
Memory manager tracks, sizes and controls allocation. Paging: fixed-size pages and frames, internal fragmentation. Segmentation: variable logical segments, exte - Binary and hexadecimal
Bits are powers of 2; one hex digit = 4 bits; A to F are 10 to 15. - Units of data: bits, bytes, binary and decimal prefixes
Nibble 4 bits, byte 8 bits; n bits give 2n states. KiB, MiB, GiB, TiB are powers of 1024 for sizes; k, M, G, T are powers of 1000 for speeds. - Two's complement: representing signed integers
MSB has place value -2n-1. Negate: invert then add 1. 8-bit range -128 to 127; one zero; subtraction by addition. - Fixed-point binary: signed fractional numbers
Point fixed by agreement; places after it are 1/2, 1/4, 1/8; MSB negative in two's complement. Fewer fraction bits: more range, less precision. - Binary addition, subtraction, overflow and underflow
1 + 1 = 10, 1 + 1 + 1 = 11. A - B = A + (two's complement of B), discard the carry out. Overflow: result too big in size (positive or negative); underflow: too - Bitwise manipulation: shifts and bit masks
Logical shift: 0s fill the gap. Arithmetic right shift: copies of the sign bit fill. AND mask checks or clears, OR sets, XOR toggles. - Character encoding: ASCII, extended ASCII, Unicode and UTF-8
ASCII 7 bits, 128 codes; extended ASCII 8 bits, 256 codes; Unicode code points for every writing system; UTF-8 uses 1 to 4 bytes and matches ASCII for the first - Network components and transmission media
NIC connects a device (MAC address); switch connects devices on a LAN using MAC addresses; router links networks using IP addresses; modem converts signals; WAP - Network performance: bandwidth, transfer rate, latency and range
Bandwidth = maximum capacity; transfer rate = actual rate; latency = delay in ms; range = distance. time = size in bits / rate in bit/s (binary units for size, - Network addressing: IPv4, IPv6 and MAC addresses
IPv4: 32 bits, four denary octets, 232 addresses. IPv6: 128 bits, eight groups of 4 hex digits, 2128. MAC: 48 bits, six hex pairs, fixed to the NIC; routers u - Encryption: symmetric and asymmetric methods
Plaintext + key + algorithm gives ciphertext. Symmetric: one shared key, fast, key exchange problem. Asymmetric: public key encrypts, matching private key decry - Monoalphabetic substitution and Vernam ciphers
Monoalphabetic: each letter always maps to the same letter; broken by frequency analysis. Vernam: XOR with a truly random, single-use key as long as the message - Entity-relationship modelling: entities, keys and relationships
Entity = table; attribute = field; primary key unique; composite key = several attributes; foreign key links to another table's primary key. Foreign key on the - The logical schema: tables, data types and integrity constraints
Relation = table, attribute = column, tuple = row. Entity integrity: primary key unique and not null. Referential integrity: foreign key matches an existing pri - Data structures: arrays, lists, dictionaries, records, tuples and sets
Array: fixed size, one type, indexed. List: resizable. Dictionary: unique keys to values. Record: named fields of mixed types. Tuple: immutable. Set: unordered, - Abstract data types: stacks and queues
Stack LIFO: push to top, pop from top, overflow when full, underflow when empty. Queue FIFO: enqueue at rear, dequeue at front. Both are ADTs defined by their o - Algorithms, efficiency, logic errors and trace tables
Algorithm: finite, unambiguous steps. Flowchart: terminator, process, input/output, decision. Efficiency: how steps grow with n. Logic errors give wrong results - Recursion and tracing recursive algorithms
Recursion: base case stops it, recursive case moves towards it. Each call pushes a stack frame; results return in reverse order. Missing base case gives stack o - Searching: linear search and binary search
Linear: any order, up to n comparisons, stop early on sorted data. Binary: sorted data only, mid = (low + high) // 2, discard half each time, about log2 n compa - Sorting: bubble sort and insertion sort
Bubble sort: compare and swap neighbours, largest item ends up last each pass, stop after a pass with no swaps. Insertion sort: insert each item into the sorted - Boolean expressions and truth tables
AND both 1; OR at least one 1; XOR exactly one 1; NAND and NOR invert AND and OR. Precedence: brackets, NOT, AND, OR. n inputs give 2n rows. - Programming paradigms: procedural and declarative
Procedural: step-by-step instructions (how), subroutines, changing variables. Declarative: describe the result (what), e.g. SQL; the system decides how. - Big data, its infrastructure and data science techniques
Five Vs: volume, velocity, variety, veracity, value. Infrastructure: collection, storage, processing, modelling and analysis, networking, security. Data science - Artificial intelligence and machine learning
Narrow AI does one task (all real AI today); general AI would match humans across tasks; super AI would exceed them. Supervised ML uses labelled data (classific - Large language models
LLMs predict the next token from patterns in huge text data. Accuracy depends on the prompt and context; knowledge stops at the training cut-off; they can hallu - Development tools: IDEs and version control
IDE: editor with highlighting, autocomplete, syntax checker, debugger (breakpoints, stepping, memory inspection). VCS: repository, commits, branches, merging, r - Open-source technologies and APIs
Open source: source code available to view, modify and share under a licence; free and adaptable but variable support. API: defined interface letting software u - Unit 1 exam technique: the WCP01 paper
80 marks in 1 hour 30 minutes, no calculator, all questions compulsory, Python-style code. Explain = point plus reason; show working; use precise terms; about a
Next exams for WCP01
- Summer 2027: Tue 11 May 2027, morning, 1h 30m
From Pearson's final timetables. All exam dates. Always confirm your entries with your exams officer.