Meta tags:

Headings (most frequently used words):

edit, register, navigation, tools, renaming, contents, problem, approach, data, hazards, architectural, versus, physical, registers, history, references, menu, tag, indexed, file, reservation, stations, comparison, between, the, schemes, personal, namespaces, views, search, contribute, print, export, languages,

Text of the page (most frequently used words):
the (256), #register (78), and (72), instruction (51), file (47), are (43), this (40), registers (37), for (35), instructions (31), from (29), that (29), tag (29), order (27), #renaming (24), unit (23), can (23), machine (22), write (20), data (20), memory (20), have (20), indexed (20), with (19), bit (19), issue (19), reservation (19), processor (18), buffer (18), execution (18), architectural (18), physical (17), read (16), out (16), ready (16), has (15), value (15), future (14), every (14), which (14), not (13), architecture (13), branch (13), queue (13), used (13), these (13), written (13), there (13), all (12), program (12), rob (12), when (12), edit (11), more (11), station (11), number (11), one (11), tags (11), per (10), power (10), processing (10), also (10), than (10), queues (10), locations (10), entries (10), each (10), wikipedia (9), article (9), history (9), first (9), large (9), usually (9), values (9), into (9), may (8), performance (8), set (8), state (8), many (8), logical (8), rename (8), scheme (8), reorder (8), results (8), stations (8), new (8), code (8), articles (7), point (7), cache (7), files (7), some (7), would (7), because (7), must (7), will (7), but (7), graduation (7), location (7), dependencies (7), non (6), use (6), was (6), last (6), computer (6), chip (6), floating (6), core (6), false (6), dependency (6), operand (6), alpha (6), x86 (6), storage (6), processors (6), been (6), different (6), result (6), issued (6), broadcast (6), execute (6), then (6), operands (6), corresponding (6), reads (6), style (6), remap (6), after (6), displaystyle (6), page (5), design (5), quantum (5), logic (5), store (5), functional (5), size (5), system (5), second (5), operations (5), isa (5), microarchitecture (5), machines (5), turing (5), other (5), cams (5), small (5), most (5), prf (5), just (5), schemes (5), latency (5), between (5), integer (5), executed (5), bits (5), renamed (5), while (5), three (5), names (5), text (4), learn (4), main (4), citations (4), microprocessor (4), management (4), decoder (4), cpu (4), status (4), load (4), fifo (4), variable (4), cycle (4), associative (4), pipelined (4), hazards (4), risc (4), mips (4), sets (4), automaton (4), precise (4), references (4), both (4), pentium (4), how (4), ram (4), separate (4), priority (4), encoding (4), they (4), yet (4), entry (4), typically (4), misprediction (4), mispredictions (4), their (4), referenced (4), free (4), before (4), old (4), those (4), particular (4), programs (4), about (3), additional (3), special (3), help (3), random (3), contents (3), navigation (3), talk (3), multiple (3), issues (3), august (3), 2015 (3), org (3), array (3), hardware (3), digital (3), general (3), cpus (3), clock (3), signal (3), address (3), counter (3), control (3), generation (3), units (3), network (3), package (3), stream (3), speculative (3), parallelism (3), prediction (3), wide (3), comparison (3), access (3), cellular (3), stored (3), pleszkun (3), doi (3), interrupts (3), smith (3), such (3), amd (3), cam (3), combination (3), structure (3), early (3), original (3), had (3), until (3), decode (3), problem (3), where (3), larger (3), consumes (3), time (3), still (3), very (3), well (3), collapse (3), unused (3), simpler (3), bypass (3), better (3), smaller (3), stage (3), directly (3), either (3), require (3), cause (3), copied (3), marked (3), matching (3), placed (3), writes (3), section (3), via (3), previous (3), since (3), any (3), various (3), them (3), reading (3), 21264 (3), robs (3), done (3), example (3), specified (3), output (3), even (3), specify (3), numbers (3), cannot (3), successive (3), approach (3), known (3), lead (3), 2048 (3), 1032 (3), remove (3), template (3), please (3), mobile (2), view (2), contact (2), privacy (2), policy (2), terms (2), using (2), june (2), 2022 (2), links (2), simple (2), english (2), pages (2), upload (2), related (2), changes (2), tools (2), recent (2), search (2), categories (2), unsourced (2), statements (2), october (2), covered (2), wikiproject (2), wikify (2), cleanup (2), lacking (2), september (2), 2014 (2), https (2), register_renaming (2), model (2), module (2), purpose (2), ppw (2), watt (2), dynamic (2), voltage (2), scaling (2), integrated (2), circuit (2), circuitry (2), barrel (2), datapath (2), microcode (2), stack (2), target (2), predictor (2), bus (2), heterogeneous (2), multi (2), single (2), count (2), others (2), 256 (2), 128 (2), word (2), gpu (2), graphics (2), coprocessor (2), application (2), vector (2), central (2), types (2), temporal (2), process (2), superscalar (2), pipelining (2), level (2), tomasulo (2), algorithm (2), pipeline (2), forwarding (2), visc (2), 360 (2), dec (2), specific (2), hierarchy (2), von (2), neumann (2), finite (2), 1145 (2), years (2), implementation (2), 1994 (2), nexgen (2), nx686 (2), cyrix (2), intel (2), implement (2), released (2), rather (2), eliminated (2), however (2), earlier (2), table (2), content (2), addressable (2), did (2), same (2), r10000 (2), much (2), area (2), parallel (2), makes (2), exception (2), discussed (2), sort (2), through (2), exceptions (2), way (2), copies (2), recover (2), case (2), looked (2), architecturally (2), outstanding (2), allocated (2), necessary (2), back (2), preceding (2), match (2), source (2), place (2), holds (2), andy (2), glew (2), close (2), together (2), possible (2), ports (2), rrf (2), retirement (2), contain (2), operation (2), flight (2), committed (2), sent (2), containing (2), might (2), port (2), input (2), physically (2), two (2), language (2), instance (2), running (2), writing (2), progress (2), versus (2), increases (2), important (2), reusing (2), without (2), requires (2), targets (2), need (2), commonly (2), provided (2), return (2), resolved (2), war (2), waw (2), referred (2), flow (2), high (2), achieve (2), independent (2), 2056 (2), 1024 (2), finish (2), consider (2), name (2), technique (2), message (2), improve (2), jump (2), web (2), cookie, statement, statistics, developers, disclaimers, available, under, apply, site, you, agree, registered, trademark, profit, organization, wikimedia, foundation, inc, creative, commons, attribution, sharealike, license, edited, utc, українська, türkçe, српски, srpski, русский, português, polski, norsk, bokmål, 日本語, italiano, français, فارسی, español, deutsch, languages, printable, version, download, pdf, print, export, wikidata, item, cite, information, permanent, link, what, here, community, portal, contribute, donate, current, events, views, namespaces, log, create, account, contributions, logged, personal, menu, hidden, 2010, maintenance, needing, introduction, retrieved, index, php, title, oldid, 1092346157, carrier, pin, grid, tick, tock, semiconductor, device, fabrication, security, electronics, chronology, gating, frequency, acpi, apm, pmu, switch, analog, boolean, mixed, shifter, sum, addressed, binary, multiplier, adder, demultiplexer, multiplexer, horizontal, rom, hardwired, gate, glue, sequential, combinational, imc, controller, mmu, tlb, translation, lookaside, fpu, agu, alu, arithmetic, rate, coherence, replacement, policies, scratchpad, components, manycore, slicing, 512, baseband, secure, cryptoprocessor, tpu, tensor, dsp, ppu, physics, vpu, vision, image, accelerator, accelerators, noc, psoc, programmable, mpsoc, multiprocessor, soc, systems, soft, asip, ultra, low, notebook, microcontroller, embedded, pop, sip, mcm, cpld, fpoa, fpga, asic, pal, tile, gpgpu, orders, magnitude, metrics, sups, synaptic, updates, tps, transactions, flops, ips, ipc, cpi, cycles, transistor, spmd, mimd, misd, swar, simt, simd, sisd, flynn, taxonomy, cooperative, preemptive, hyperthreading, simultaneous, multithreading, distributed, thread, task, scalar, serial, dependence, scoreboarding, sharing, structural, classic, stall, epiphany, tilera, 3x0, 390, 370, lmc, microblaze, openrisc, itanium, unicore, m32r, etrax, cris, superh, sparc, clipper, powerpc, stanford, arm, pdp, vax, motorola, 68000, series, addressing, modes, computing, zisc, nisc, oisc, misc, epic, vliw, trips, edge, cisc, orthogonal, architectures, neuromorphic, cognitive, multiprocessing, fabric, secondary, virtual, huma, numa, endianness, transport, triggered, dataflow, modified, harvard, pointer, belt, zeno, hypercomputation, probabilistic, nondeterministic, post, universal, alternating, deterministic, hierarchical, abstract, models, technologies, 1998, 1581130589, isbn, 285930, 285988, 291, 299, international, symposia, selected, papers, isca, 1988, implementing, 562, 573, 1109, 4607, ieee, trans, comput, 1985, 327070, 327125, acm, sigarch, news, ziff, davis, mag, 6x86, pro, iii, microprocessors, 1995, 1996, featured, native, ways, story, progressively, useful, impractical, citation, needed, renamer, hpsm, rat, alias, essentially, versions, modern, indexing, map, functions, matter, earliest, sohi, ruu, metaflow, dcaf, combined, scheduling, neither, collapsing, nor, suffered, starvation, problems, oldest, sometimes, stopped, completely, lack, later, revisions, starting, partially, encoder, mitigate, r12000, 1990, power1, supported, uses, ibm, furthermore, four, places, whereas, reach, function, equipped, accurate, latencies, major, concern, work, remarkably, serve, aggregate, consume, complicated, worse, times, networks, equivalent, consequently, local, below, finds, finding, find, shows, component, inserted, removed, empty, slots, simultaneously, holes, advance, recognized, reconstruct, intermediate, recovery, sole, arguments, mentioned, perhaps, eight, wait, see, broadcasts, unlike, gives, serially, designs, causes, valid, snapshots, cycling, pre, mechanism, required, currently, being, graduated, handled, reaches, potentially, hiding, bypassing, puts, reused, newly, decoded, against, means, matches, mark, pick, send, stay, unordered, removal, make, consuming, returns, queued, takes, pulled, mapping, refer, unready, saved, stages, athlon, proposal, insisted, complex, keith, diefendorff, don, certainly, none, designed, clear, difference, should, banked, detail, locality, sequence, perform, combining, fewer, illinois, harrm, willamette, book, keeping, buffers, less, ful, sequentially, circularly, basis, differs, comes, exists, contains, overwritten, producer, lookup, disabled, group, term, active, retired, forwarded, inputs, converts, generally, grows, square, significant, following, describes, styles, distinguished, implements, fact, extra, germane, limited, specifies, programmer, stops, debugger, observe, few, determine, misses, often, stalls, waiting, historically, changed, retaining, backwards, compatibility, specifying, resulting, increased, difficult, compiler, avoid, loops, iterations, replicating, called, utilising, change, iteration, self, modifying, loop, unrolling, refrained, immediately, specifically, reason, limitations, although, extent, practiced, gated, form, transmeta, crusoe, anything, flag, individual, instead, delaying, completed, maintained, precede, follow, broken, opportunities, created, satisfied, discarded, essential, concept, behind, prior, programmatically, anti, leave, cancelling, annulling, mooting, squashing, true, raw, executing, kinds, hazard, appropriate, detection, good, compilers, detect, sequences, choose, during, now, run, faster, obliterating, stalling, due, restriction, changing, final, lines, doing, otherwise, incorrect, piece, take, amounts, able, hundreds, shorter, thus, finishing, speed, gains, compact, correspond, elements, riscs, composed, operate, distinguish, another, typical, say, add, put, eliminate, arising, reuse, real, elimination, reveals, exploited, complementary, techniques, abstracts, associated, refers, transposes, fly, opaque, only, canonical, discuss, expanding, aspects, provide, accessible, overview, too, short, adequately, key, points, summarize, includes, list, introducing, lacks, sufficient, inline, messages, encyclopedia, wayback, http, archive, 20221015234334, wiki, timestamps, capture, fail, success, 2023, 2021, nov, oct, sep, jul, 2004, aug, 2026, captures,

Text of the page (random words):
still in flight it may be ram indexed by history buffer number after a branch misprediction must use results from the history buffer either they are copied or the future file lookup is disabled and the history buffer is content addressable memory cam indexed by logical register number reorder buffer rob a structure that is sequentially circularly indexed on a per operation basis for instructions in flight it differs from a history buffer because the reorder buffer typically comes after the future file if it exists and before the architectural register file reorder buffers can be data less or data ful in willamette s rob the rob entries point to registers in the physical register file prf and also contain other book keeping this was also the first out of order design done by andy glew at illinois with harrm p6 s rob the rob entries contain data there is no separate prf data values from the rob are copied from the rob to the rrf at retirement one small detail if there is temporal locality in rob entries i e if instructions close together in the von neumann instruction sequence write back close together in time it may be possible to perform write combining on rob entries and so have fewer ports than a separate rob prf would it is not clear if it makes a difference since a prf should be banked robs usually don t have associative logic and certainly none of the robs designed by andy glew have cams keith diefendorff insisted that robs have complex associative logic for many years the first rob proposal may have had cams tag indexed register file edit this is the renaming style used in the mips r10000 the alpha 21264 and in the fp section of the amd athlon in the renaming stage every architectural register referenced for read or write is looked up in an architecturally indexed remap file this file returns a tag and a ready bit the tag is non ready if there is a queued instruction which will write to it that has not yet executed for read operands this tag takes the place of the architectural register in the instruction for every register write a new tag is pulled from a free tag fifo and a new mapping is written into the remap file so that future instructions reading the architectural register will refer to this new tag the tag is marked as unready because the instruction has not yet executed the previous physical register allocated for that architectural register is saved with the instruction in the reorder buffer which is a fifo that holds the instructions in program order between the decode and graduation stages the instructions are then placed in various issue queues as instructions are executed the tags for their results are broadcast and the issue queues match these tags against the tags of their non ready source operands a match means that the operand is ready the remap file also matches these tags so that it can mark the corresponding physical registers as ready when all the operands of an instruction in an issue queue are ready that instruction is ready to issue the issue queues pick ready instructions to send to the various functional units each cycle non ready instructions stay in the issue queues this unordered removal of instructions from the issue queues can make them large and power consuming issued instructions read from a tag indexed physical register file bypassing just broadcast operands and then execute execution results are written to tag indexed physical register file as well as broadcast to the bypass network preceding each functional unit graduation puts the previous tag for the written architectural register into the free queue so that it can be reused for a newly decoded instruction an exception or branch misprediction causes the remap file to back up to the remap state at last valid instruction via combination of state snapshots and cycling through the previous tags in the in order pre graduation queue since this mechanism is required and since it can recover any remap state not just the state before the instruction currently being graduated branch mispredictions can be handled before the branch reaches graduation potentially hiding the branch misprediction latency reservation stations edit main article reservation station this is the style used in the integer section of the amd k7 and k8 designs in the renaming stage every architectural register referenced for reads is looked up in both the architecturally indexed future file and the rename file the future file read gives the value of that register if there is no outstanding instruction yet to write to it i e it s ready when the instruction is placed in an issue queue the values read from the future file are written into the corresponding entries in the reservation stations register writes in the instruction cause a new non ready tag to be written into the rename file the tag number is usually serially allocated in instruction order no free tag fifo is necessary just as with the tag indexed scheme the issue queues wait for non ready operands to see matching tag broadcasts unlike the tag indexed scheme matching tags cause the corresponding broadcast value to be written into the issue queue entry s reservation station issued instructions read their arguments from the reservation station bypass just broadcast operands and then execute as mentioned earlier the reservation station register files are usually small with perhaps eight entries execution results are written to the reorder buffer to the reservation stations if the issue queue entry has a matching tag and to the future file if this is the last instruction to target that architectural register in which case register is marked ready graduation copies the value from the reorder buffer into the architectural register file the sole use of the architectural register file is to recover from exceptions and branch mispredictions exceptions and branch mispredictions recognized at graduation cause the architectural file to be copied to the future file and all registers marked as ready in the rename file there is usually no way to reconstruct the state of the future file for some instruction intermediate between decode and graduation so there is usually no way to do early recovery from branch mispredictions comparison between the schemes edit in both schemes instructions are inserted in order into the issue queues but are removed out of order if the queues do not collapse empty slots then they will either have many unused entries or require some sort of variable priority encoding for when multiple instructions are simultaneously ready to go queues that collapse holes have simpler priority encoding but require simple but large circuitry to advance instructions through the queue reservation stations have better latency from rename to execute because the rename stage finds the register values directly rather than finding the physical register number and then using that to find the value this latency shows up as a component of the branch misprediction latency reservation stations also have better latency from instruction issue to execution because each local register file is smaller than the large central file of the tag indexed scheme tag generation and exception processing are also simpler in the reservation station scheme as discussed below the physical register files used by reservation stations usually collapse unused entries in parallel with the issue queue they serve which makes these register files larger in aggregate and consume more power and more complicated than the simpler register files used in a tag indexed scheme worse yet every entry in each reservation station can be written by every result bus so that a reservation station machine with e g 8 issue queue entries per functional unit will typically have 9 times as many bypass networks as an equivalent tag indexed machine consequently result forwarding consumes much more power and area than in a tag indexed design furthermore the reservation station scheme has four places future file reservation station reorder buffer and architectural file where a result value can be stored whereas the tag indexed scheme has just one the physical register file because the results from the functional units broadcast to all these storage locations must reach a much larger number of locations in the machine than in the tag indexed scheme this function consumes more power area and time still in machines equipped with very accurate branch prediction schemes and if execute latencies are a major concern reservation stations can work remarkably well history edit the ibm system 360 model 91 was an early machine that supported out of order execution of instructions it used the tomasulo algorithm which uses register renaming the power1 is the first microprocessor that used register renaming and out of order execution in 1990 the original r10000 design had neither collapsing issue queues nor variable priority encoding and suffered starvation problems as a result the oldest instruction in the queue would sometimes not be issued until both instruction decode stopped completely for lack of rename registers and every other instruction had been issued later revisions of the design starting with the r12000 used a partially variable priority encoder to mitigate this problem early out of order machines did not separate the renaming and rob prf storage functions for that matter some of the earliest such as sohi s ruu or the metaflow dcaf combined scheduling renaming and storage all in the same structure most modern machines do renaming by ram indexing a map table with the logical register number e g p6 did this future files do this and have data storage in the same structure however earlier machines used content addressable memory cam in the renamer e g the hpsm rat or register alias table essentially used a cam on the logical register number in combination with different versions of the register in many ways the story of out of order microarchitecture has been how these cams have been progressively eliminated small cams are useful large cams are impractical citation needed the p6 microarchitecture was the first microarchitecture by intel to implement both out of order execution and register renaming the p6 microarchitecture was used in pentium pro pentium ii pentium iii pentium m core and core 2 microprocessors the cyrix m1 released on october 2 1995 1 was the first x86 processor to use register renaming and out of order execution other x86 processors such as nexgen nx686 and amd k5 released in 1996 also featured register renaming and out of order execution of risc μ operations rather than native x86 instructions 2 3 references edit cyrix 6x86 processor nexgen nx686 pc mag dec 6 1994 ziff davis 1994 12 06 smith j e pleszkun a r june 1985 implementation of precise interrupts in pipelined processors acm sigarch computer architecture news 13 3 36 44 doi 10 1145 327070 327125 smith j e pleszkun a r may 1988 implementing precise interrupts in pipelined processors ieee trans comput 37 5 562 573 doi 10 1109 12 4607 smith j e pleszkun a r 1998 implementation of precise interrupts in pipelined processors 25 years of the international symposia on computer architecture selected papers isca 98 pp 291 299 doi 10 1145 285930 285988 isbn 1581130589 v t e processor technologies models abstract machine stored program computer finite state machine with datapath hierarchical deterministic finite automaton queue automaton cellular automaton quantum cellular automaton turing machine alternating turing machine universal post turing quantum nondeterministic turing machine probabilistic turing machine hypercomputation zeno machine belt machine stack machine register machines counter pointer random access random access stored program architecture microarchitecture von neumann harvard modified dataflow transport triggered cellular endianness memory access numa huma load store register memory cache hierarchy memory hierarchy virtual memory secondary storage heterogeneous fabric multiprocessing cognitive neuromorphic instruction set architectures types orthogonal instruction set cisc risc application specific edge trips vliw epic misc oisc nisc zisc visc architecture quantum computing comparison addressing modes instruction sets motorola 68000 series vax pdp 11 x86 arm stanford mips mips mips x power power powerpc power isa clipper architecture sparc superh dec alpha etrax cris m32r unicore itanium openrisc risc v microblaze lmc system 3x0 s 360 s 370 s 390 z architecture tilera isa visc architecture epiphany architecture others execution instruction pipelining pipeline stall operand forwarding classic risc pipeline hazards data dependency structural control false sharing out of order scoreboarding tomasulo algorithm reservation station re order buffer register renaming wide issue speculative branch prediction memory dependence prediction parallelism level bit bit serial word instruction pipelining scalar superscalar task thread process data vector memory distributed multithreading temporal simultaneous hyperthreading speculative preemptive cooperative flynn s taxonomy sisd simd array processing simt pipelined processing associative processing swar misd mimd spmd processor performance transistor count instructions per cycle ipc cycles per instruction cpi instructions per second ips floating point operations per second flops transactions per second tps synaptic updates per second sups performance per watt ppw cache performance metrics computer performance by orders of magnitude types central processing unit cpu graphics processing unit gpu gpgpu vector barrel stream tile processor coprocessor pal asic fpga fpoa cpld multi chip module mcm system in a package sip package on a package pop by application embedded system microprocessor microcontroller mobile notebook ultra low voltage asip soft microprocessor systems on chip system on a chip soc multiprocessor mpsoc programmable psoc network on a chip noc hardware accelerators coprocessor ai accelerator graphics processing unit gpu image processor vision processing unit vpu physics processing unit ppu digital signal processor dsp tensor processing unit tpu secure cryptoprocessor network processor baseband processor word size 1 bit 4 bit 8 bit 12 bit 15 bit 16 bit 24 bit 32 bit 48 bit 64 bit 128 bit 256 bit 512 bit bit slicing others variable core count single core multi core manycore heterogeneous architecture components core cache cpu cache scratchpad memory data cache instruction cache replacement policies coherence bus clock rate clock signal fifo functional units arithmetic logic unit alu address generation unit agu floating point unit fpu memory management unit mmu load store unit translation lookaside buffer tlb branch predictor branch target predictor integrated memory controller imc memory management unit instruction decoder logic combinational sequential glue logic gate quantum array registers processor register status register stack register regi...