IB Computer Science HL – Topic 6: Resource Management

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6.1.1 Resources that need to be managed

Main groups

Storage	Processing	I/O
• Cache & RAM (primary) • Secondary storage • Disk capacity	• CPU speed (clock rate) • # of cores • Specialised chips (GPU, sound)	• Bandwidth • Screen resolution • Network connectivity • Peripherals 外围设备

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6.1.2 Evaluating resources in different computer systems

• Supercomputers – maximise raw computation for simulations. Emphasis on massive parallel CPU/GPU, less on user I/O.

• Mainframes – always-on, high I/O throughput for transactions; redundant RAM, storage & bandwidth.

• Servers – balance network bandwidth, storage and RAM to serve many clients concurrently.

• PCs / laptops / chromebooks – general purpose; specs vary with use-case (e.g. gamers add GPU & RAM).

• Mobile devices (smartphones, tablets) – convergent tech; limited by size & battery but now powerful CPUs/GPUs.

• Specialised devices (DSLRs, GoPros, PDAs) – optimised for narrow tasks; minimal extra resources.

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6.1.3 Typical resource limitations & their effects

Resource	Too little leads to…
CPU speed / cores	Long execution times; poor parallelism
RAM	Thrashing: constant paging to disk
Disk space	Unable to install / store data
Swap / paging file	Virtual memory can’t expand
Bandwidth	IO waits dominate, low throughput
GPU absence	CPU bound for graphics

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Core operating-system strategies (HL extension)

• Multi-tasking – scheduler shares CPU via: time-slicing, prioritisation, round-robin, FIFO.

• Multi-processing – extra cores or dedicated GPUs add power but add scheduling complexity.

• Polling vs Interrupts – polling wastes CPU; interrupts save time but too many = overhead. Default: use interrupts for most devices.

• Blocking & Swapping – when process waits on I/O, OS swaps it out, freeing RAM.

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Memory-management concepts

paging: - memory management method that uses secondary memory to increase the amount of primary memory; - transfers data blocks of the same size (“pages”); - from secondary storage to main storage when they are required; - and returns them to secondary storage when they are not;

Term	What it means	Why it matters
==Paging==	Split RAM into equal pages; processes can occupy non-contiguous pages	Reduces external fragmentation but causes internal fragmentation.
Virtual Memory	Presents each process with a contiguous address space starting at 0; MMU maps to real RAM/disk	More processes can run than fit in RAM – classic abstraction.
Fragmentation	External – gaps between blocks; Internal – unused space inside pages	Defragment disks (not needed on SSDs).

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Multi-user & dedicated OS environments

• Single-user single-task (old Palm OS) → one program, one user.

• Single-user multi-tasking (macOS, Windows) → one user, many processes.

• Multi-user (Windows Server, Unix servers) → OS protects each user’s data & processes.

• Dedicated / real-time OS – optimised for niche hardware or fast, deterministic response (e.g. QNX for medical devices).

==role of OS in terms of resource management==: - OS is an interface between user and hardware. It plays a role of allocating resources to tasks and users, keeping track of the current user, mediate resource conflicts.

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Virtualisation examples

• Virtual memory & virtual storage letters hide hardware complexity.

• JVM abstracts OS differences: “write once, run anywhere”.

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Exam snapshot

• IB allocates ~9 teaching hours → ≈ 7 marks in Paper 1 (but past papers sometimes give fewer). Focus on definitions + clear examples.

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Tip for revision:
Practise the IB command terms:

• Identify = name a resource.

• Evaluate = discuss pros/cons in context.

• Discuss = balanced argument (e.g. interrupts vs polling).
  Link every answer back to how effective resource use ↑ overall system performance.

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Patch

virtual machine: 1. a program 2. that imitates an OS environment 3. in another OS 4. to abstractify hardware details

Interrupt definition: a signal sent to the processor to suspend current task (and work on the interrupting one)