Operating Systems workbook: foundations, CPU/memory virtualization, concurrency, persistence, and real OS systems.http://localhost:4321/http://localhost:4321/operating-systems/address-translation-base-bounds/http://localhost:4321/operating-systems/address-translation-base-bounds/The simplest hardware mechanism for memory virtualization — relocation registers, bounds checks, OS responsibilities.Sun, 24 May 2026 00:00:00 GMTIntermediatebuilding-blockMemory Virtualizationbase-boundsrelocationmmuaddress-translationdynamic-relocationhttp://localhost:4321/operating-systems/address-spaces/http://localhost:4321/operating-systems/address-spaces/Code / heap / stack layout, why each process gets its own view, and the three goals (transparency, efficiency, protection).Sun, 24 May 2026 00:00:00 GMTFoundationalconceptMemory Virtualizationaddress-spacevirtual-memoryprocesslayoutisolationhttp://localhost:4321/operating-systems/afs-andrew-file-system/http://localhost:4321/operating-systems/afs-andrew-file-system/Whole-file caching, callbacks for invalidation, last-writer-wins, and how AFS achieved campus-scale before the cloud.Sun, 24 May 2026 00:00:00 GMTAdvancedsystemDistributiondistributed-fscachingcallbacksafshttp://localhost:4321/operating-systems/concurrency-bugs/http://localhost:4321/operating-systems/concurrency-bugs/Non-deadlock vs deadlock bugs; the four conditions for deadlock; prevention, avoidance, detection-and-recovery.Sun, 24 May 2026 00:00:00 GMTIntermediateconceptConcurrencydeadlockrace-conditionsatomicity-violationdebugginghttp://localhost:4321/operating-systems/concurrent-data-structures/http://localhost:4321/operating-systems/concurrent-data-structures/Concurrent counters, linked lists, queues, and hash tables — coarse-grained vs hand-over-hand vs lock-free, and where each one breaks under contention.Sun, 24 May 2026 00:00:00 GMTIntermediatebuilding-blockConcurrencyconcurrent-data-structureslock-freescalingcontentionhttp://localhost:4321/operating-systems/context-switching/http://localhost:4321/operating-systems/context-switching/Saving and restoring CPU state across processes — register sets, kernel stack, the cost paid every preemption.Sun, 24 May 2026 00:00:00 GMTIntermediatebuilding-blockCPU Virtualizationcontext-switchregisterskernel-stacktlbschedulerhttp://localhost:4321/operating-systems/cpu-scheduling-basics/http://localhost:4321/operating-systems/cpu-scheduling-basics/Four classic scheduling disciplines, their turnaround / response-time trade-offs, and where each breaks down.Sun, 24 May 2026 00:00:00 GMTFoundationalbuilding-blockCPU Virtualizationschedulingfifosjfstcfround-robinturnaroundresponse-timehttp://localhost:4321/operating-systems/data-integrity-checksums/http://localhost:4321/operating-systems/data-integrity-checksums/Latent sector errors, silent corruption, checksums, mismatched-write protection, periodic scrubbing — bit-rot defense.Sun, 24 May 2026 00:00:00 GMTIntermediatebuilding-blockPersistencedata-integritychecksumscrubbingbit-rotdurabilityhttp://localhost:4321/operating-systems/distributed-systems-comm-basics/http://localhost:4321/operating-systems/distributed-systems-comm-basics/Unreliable vs reliable channels, RPC, idempotency, timeout / retry / at-most-once / at-least-once semantics.Sun, 24 May 2026 00:00:00 GMTIntermediateconceptDistributionrpcidempotencytimeoutsretriesnetworkinghttp://localhost:4321/operating-systems/event-based-concurrency/http://localhost:4321/operating-systems/event-based-concurrency/Event loops, select / poll / epoll, async I/O, the manual state-management cost, and why JS, Nginx, and Node landed here.Sun, 24 May 2026 00:00:00 GMTAdvancedbuilding-blockConcurrencyevent-loopepollasync-iononblockinglibeventhttp://localhost:4321/operating-systems/fast-file-system-ffs/http://localhost:4321/operating-systems/fast-file-system-ffs/Cylinder groups, locality policy, large-file exception — the design that made UNIX file systems orders of magnitude faster.Sun, 24 May 2026 00:00:00 GMTIntermediatesystemPersistenceffsfile-systemlocalitycylinder-groupunixhttp://localhost:4321/operating-systems/file-system-implementation/http://localhost:4321/operating-systems/file-system-implementation/Inode + data-block layout, free-space tracking, directory structures, access paths, caching, and the I/O cost per system call.Sun, 24 May 2026 00:00:00 GMTIntermediatebuilding-blockPersistencefile-systeminodelayoutpage-cachedirectoryhttp://localhost:4321/operating-systems/free-space-management/http://localhost:4321/operating-systems/free-space-management/Allocator strategies — first-fit, best-fit, worst-fit, next-fit, segregated free lists, buddy, slab — and what fragmentation actually costs.Sun, 24 May 2026 00:00:00 GMTIntermediatebuilding-blockMemory Virtualizationallocatorfragmentationfree-listbuddyslabhttp://localhost:4321/operating-systems/flash-ssds-and-ftl/http://localhost:4321/operating-systems/flash-ssds-and-ftl/Cells, banks, planes; erase-before-write; the FTL log-structured mapping; garbage collection; wear leveling; trim.Sun, 24 May 2026 00:00:00 GMTAdvancedbuilding-blockPersistencessdflashftlwear-levelinggarbage-collectionhttp://localhost:4321/operating-systems/files-and-directories/http://localhost:4321/operating-systems/files-and-directories/The UNIX file abstraction, descriptors, inodes, hard vs symbolic links, fsync, mount, and the permission-bit model.Sun, 24 May 2026 00:00:00 GMTFoundationalbuilding-blockPersistencefilesdirectoriesinodeslinksfsynchttp://localhost:4321/operating-systems/gitlab-2017-data-loss/http://localhost:4321/operating-systems/gitlab-2017-data-loss/How a 'wrong terminal' rm on a primary led to ~6 hours of data loss; backups that didn't work; the public postmortem.Sun, 24 May 2026 00:00:00 GMTFoundationalpostmortemPersistencepostmortembackupsdata-lossrunbookshttp://localhost:4321/operating-systems/hard-disk-drives/http://localhost:4321/operating-systems/hard-disk-drives/Geometry, seek + rotational latency + transfer time, disk scheduling (SSTF, SCAN, C-SCAN), and the I/O-cost math.Sun, 24 May 2026 00:00:00 GMTFoundationalbuilding-blockPersistencehdddiskschedulinglatencystoragehttp://localhost:4321/operating-systems/io-devices-and-drivers/http://localhost:4321/operating-systems/io-devices-and-drivers/The canonical device protocol, interrupts vs polling, DMA, memory-mapped I/O, and the driver as an OS abstraction.Sun, 24 May 2026 00:00:00 GMTFoundationalbuilding-blockPersistenceiodriversdmainterruptsmmiohttp://localhost:4321/operating-systems/linux-virtual-memory/http://localhost:4321/operating-systems/linux-virtual-memory/The Linux address space layout, four-level page tables, page cache, huge pages, KASLR — what a real production VM stack looks like.Sun, 24 May 2026 00:00:00 GMTAdvancedsystemMemory Virtualizationlinuxvmpage-cachekaslrkptitransparent-hugepageshttp://localhost:4321/operating-systems/limited-direct-execution/http://localhost:4321/operating-systems/limited-direct-execution/How the CPU runs user code at full speed while the OS still keeps control — traps, trampolines, timer interrupts.Sun, 24 May 2026 00:00:00 GMTIntermediateconceptFoundationsldetrapstimer-interruptpreemptionsyscallshttp://localhost:4321/operating-systems/locks-and-spinlocks/http://localhost:4321/operating-systems/locks-and-spinlocks/Test-and-set, compare-and-swap, fetch-and-add, two-phase locks, and why a spinlock is rarely the right answer in user space.Sun, 24 May 2026 00:00:00 GMTIntermediatebuilding-blockConcurrencylocksmutexspinlockatomicsfutexhttp://localhost:4321/operating-systems/log-structured-file-system-lfs/http://localhost:4321/operating-systems/log-structured-file-system-lfs/Sequential writes, segments, inode maps, garbage collection — the design that influenced flash file systems and modern databases.Sun, 24 May 2026 00:00:00 GMTAdvancedsystemPersistencelfslog-structuredsequential-writegarbage-collectionfile-systemhttp://localhost:4321/operating-systems/lottery-and-cfs/http://localhost:4321/operating-systems/lottery-and-cfs/Probabilistic fair-share scheduling, ticket mechanisms, and how CFS uses red-black trees for O(log n) operations.Sun, 24 May 2026 00:00:00 GMTIntermediatebuilding-blockCPU Virtualizationschedulinglotterycfsfair-sharered-black-treevruntimehttp://localhost:4321/operating-systems/memory-api-malloc-free/http://localhost:4321/operating-systems/memory-api-malloc-free/Heap allocation in user space, common errors (use-after-free, double-free, leaks), and how the allocator talks to the OS via brk / mmap.Sun, 24 May 2026 00:00:00 GMTFoundationalbuilding-blockMemory Virtualizationmallocfreeheapallocatormmapbrkhttp://localhost:4321/operating-systems/mlfq-scheduling/http://localhost:4321/operating-systems/mlfq-scheduling/Adaptive priority queues, priority boosts to prevent starvation, accounting tricks to defeat gaming.Sun, 24 May 2026 00:00:00 GMTIntermediatebuilding-blockCPU Virtualizationmlfqschedulingprioritystarvationgaminghttp://localhost:4321/operating-systems/multi-cpu-scheduling/http://localhost:4321/operating-systems/multi-cpu-scheduling/Cache affinity, single-queue vs per-CPU queues, load balancing, and why scaling beyond one core is hard.Sun, 24 May 2026 00:00:00 GMTAdvancedconceptCPU Virtualizationsmpmulticorecache-affinityload-balancingnumahttp://localhost:4321/operating-systems/multi-level-page-tables/http://localhost:4321/operating-systems/multi-level-page-tables/Sparse address spaces, x86_64's 4-level walk, the time-space trade-off, inverted page tables, hashed alternatives.Sun, 24 May 2026 00:00:00 GMTAdvancedbuilding-blockMemory Virtualizationpage-tablemulti-levelx86-64sparsepage-walkhttp://localhost:4321/operating-systems/nfs-network-file-system/http://localhost:4321/operating-systems/nfs-network-file-system/Stateless protocol, idempotent operations, client-side caching, the cache-consistency problem, server-write buffering.Sun, 24 May 2026 00:00:00 GMTIntermediatesystemDistributionnfsdistributed-file-systemssun-rpcstatelessnesshttp://localhost:4321/operating-systems/os-design-goals/http://localhost:4321/operating-systems/os-design-goals/Abstractions, low overhead, protection and isolation, reliability. The criteria every kernel decision is weighed against.Sun, 24 May 2026 00:00:00 GMTFoundationalconceptFoundationsos-fundamentalsdesign-goalsabstractionsisolationreliabilityhttp://localhost:4321/operating-systems/page-replacement-policies/http://localhost:4321/operating-systems/page-replacement-policies/The classic algorithms, why OPT is unachievable, how CLOCK approximates LRU cheaply, and the thrashing wall.Sun, 24 May 2026 00:00:00 GMTIntermediatebuilding-blockMemory Virtualizationpage-replacementlruclockthrashingworking-sethttp://localhost:4321/operating-systems/process-abstraction/http://localhost:4321/operating-systems/process-abstraction/Process state (running / ready / blocked), address space, PCB, and the kernel's view of a running program.Sun, 24 May 2026 00:00:00 GMTFoundationalconceptCPU Virtualizationprocesspcbprocess-stateaddress-spacekernelhttp://localhost:4321/operating-systems/pthreads-api/http://localhost:4321/operating-systems/pthreads-api/pthread_create / join / mutex / cond — the canonical thread surface and the gotchas around using it correctly.Sun, 24 May 2026 00:00:00 GMTFoundationalbuilding-blockConcurrencypthreadsposixthreading-apiglibchttp://localhost:4321/operating-systems/raid/http://localhost:4321/operating-systems/raid/RAID 0/1/4/5/6 — capacity, performance, reliability trade-offs and where parity-based schemes break down.Sun, 24 May 2026 00:00:00 GMTIntermediatebuilding-blockPersistenceraidredundancyparitymirroringstoragehttp://localhost:4321/operating-systems/segmentation/http://localhost:4321/operating-systems/segmentation/Generalised base/bounds per code/heap/stack segment, sharing across processes, fragmentation as the recurring cost.Sun, 24 May 2026 00:00:00 GMTIntermediatebuilding-blockMemory Virtualizationsegmentationsegmentssharingfragmentationx86http://localhost:4321/operating-systems/semaphores/http://localhost:4321/operating-systems/semaphores/Counting semaphores as a generalisation of locks; binary semaphores; ordering; readers-writers; dining philosophers.Sun, 24 May 2026 00:00:00 GMTIntermediatebuilding-blockConcurrencysemaphoressynchronizationproducer-consumerdijkstrahttp://localhost:4321/operating-systems/swapping-mechanisms/http://localhost:4321/operating-systems/swapping-mechanisms/Swap space, the present bit, page fault control flow, copy-on-write, prefetching, and when replacements actually happen.Sun, 24 May 2026 00:00:00 GMTIntermediatebuilding-blockMemory Virtualizationswappage-faultdemand-pagingcopy-on-writepresent-bithttp://localhost:4321/operating-systems/threads-and-shared-state/http://localhost:4321/operating-systems/threads-and-shared-state/Why threads, the heart of the problem (uncontrolled scheduling), atomicity, and the wish that motivates every primitive.Sun, 24 May 2026 00:00:00 GMTFoundationalconceptConcurrencythreadsshared-stateatomicityrace-conditionshttp://localhost:4321/operating-systems/tlbs/http://localhost:4321/operating-systems/tlbs/The cache that makes paging fast. Miss handling (HW vs SW), context-switch invalidation, ASIDs, and a real TLB entry's bits.Sun, 24 May 2026 00:00:00 GMTIntermediatebuilding-blockMemory Virtualizationtlbmmupage-walkasidaddress-translationhttp://localhost:4321/operating-systems/user-mode-vs-kernel-mode/http://localhost:4321/operating-systems/user-mode-vs-kernel-mode/Hardware privilege levels, system calls, trap-and-emulate, and the cost of crossing the boundary.Sun, 24 May 2026 00:00:00 GMTFoundationalconceptFoundationsprivilege-levelssystem-callstrapsring-0syscallhttp://localhost:4321/operating-systems/condition-variables/http://localhost:4321/operating-systems/condition-variables/Wait / signal / broadcast, the always-use-while rule, the producer-consumer pattern, covering conditions.Sun, 17 May 2026 00:00:00 GMTIntermediatebuilding-blockConcurrencycondition-variablessynchronizationpthreadsproducer-consumerhttp://localhost:4321/operating-systems/crash-consistency-journaling/http://localhost:4321/operating-systems/crash-consistency-journaling/Write-ahead logging, metadata-only vs full journaling, ordered mode, soft updates, and why fsck stopped scaling.Sun, 17 May 2026 00:00:00 GMTIntermediatebuilding-blockPersistencecrash-consistencyjournalingfile-systemwrite-ahead-logfsckhttp://localhost:4321/operating-systems/paging-fundamentals/http://localhost:4321/operating-systems/paging-fundamentals/Fixed-size pages, page tables, valid / present / protection bits, and the cost paid on every memory access without a cache.Sun, 17 May 2026 00:00:00 GMTIntermediatebuilding-blockMemory Virtualizationpagingpage-tablemmuvirtual-memoryaddress-translationhttp://localhost:4321/operating-systems/process-api-fork-exec-wait/http://localhost:4321/operating-systems/process-api-fork-exec-wait/The UNIX trio that creates and controls processes. Why fork+exec is the standard idiom and what dup/pipe add on top.Sun, 17 May 2026 00:00:00 GMTFoundationalbuilding-blockCPU Virtualizationprocess-apiforkexecposixunixhttp://localhost:4321/operating-systems/what-is-an-os/http://localhost:4321/operating-systems/what-is-an-os/The three jobs of an OS — virtualize hardware, manage concurrency, persist state — and why each one matters.Sun, 17 May 2026 00:00:00 GMTFoundationalconceptFoundationsos-fundamentalskernelabstractionsvirtualization