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Ignition systems are not required for diesel engines which rely on compression to ignite the fuel air mixture

An ignition coil consists of a laminated iron core surrounded by two coils of copper wire Unlike a power transformer an ignition coil has an open magnetic circuit the iron core does not form a closed loop around the windings The energy that is stored in the magnetic field of the core is the energy that is transferred to the spark plug

The primary winding has relatively few turns of heavy wire The secondary winding consists of thousands of turns of smaller wire insulated from the high voltage by enamel on the wires and layers of oiled paper insulation The coil is usually inserted into a metal can or plastic case with insulated terminals for the high voltage and low voltage connections When the contact breaker closes it allows current from the battery to flow through the primary winding of the ignition coil The current does not flow instantly because of the inductance of the coil Current flowing in the coil produces a magnetic field in the core and in the air surrounding the core The current must flow long enough to store enough energy in the field for the spark Once the current has built up to its full level the contact breaker opens Since it has a capacitor connected across it the primary winding and the capacitor form a tuned circuit and as the stored energy oscillates between the inductor formed by the coil and the capacitor the changing magnetic field in the core of the coil induces a much larger voltage in the secondary of the coil More modern electronic ignition systems operate on exactly the same principle but some rely on charging the capacitor to around 400 volts rather than charging the inductance of the coil The timing of the opening of the contacts or switching of the transistor must be matched to the position of the piston in the cylinder so that the spark may be timed to ignite the air fuel mixture to extract the most angular momentum possible This is usually several degrees before the piston reaches top dead center The contacts are driven off a shaft that is driven by the engine crankshaft or if electronic ignition is used a sensor on the engine shaft controls the timing of the pulses

The amount of energy in the spark required to ignite the air fuel mixture varies depending on the pressure and composition of the mixture and on the speed of the engine Under laboratory conditions as little as 1 millijoule is required in each spark but practical coils must deliver much more energy than this to allow for higher pressure rich or lean mixtures losses in ignition wiring and plug fouling and leakage When gas velocity is high in the spark gap the arc between the terminals is blown away from the terminals making the arc longer and requiring more energy in each spark Between 30 and 70 milli joules are delivered in each spark

Formerly ignition coils were made with varnish and paper insulated high voltage windings inserted into a drawn steel can and filled with oil or asphalt for insulation and moisture protection Coils on modern automobiles are cast in filled epoxy resins which penetrate any voids within the winding

A single spark system has one coil per spark plug To prevent premature sparking at the start of the primary pulse a diode or secondary spark gap is installed in the coil to block the reverse pulse that would otherwise form

In a coil meant for a dual spark system the secondary winding has two terminals isolated from the primary and each terminal connects to a spark plug With this system no extra diode is needed since there would be no fuel air mixture present at the inactive spark plug

In a low inductance coil fewer primary turns are used so primary current is higher This is not compatible with the capacity of mechanical breaker points so solid state switching is used

Early gasoline petrol internal combustion engines used a magneto ignition system since no battery was fitted to the vehicle magnetos are still used in piston engine aircraft The voltage produced by a magneto is dependent on the speed of the engine making starting difficult A battery operated coil can provide a high voltage spark even at low speeds making starting easier When batteries became common in automobiles for cranking and lighting the ignition coil system displaced magneto ignition

In older vehicles a single coil would serve all the spark plugs via the ignition distributor Notable exceptions are the Saab 92 some Volkswagens and the Wartburg 353 which have one ignition coil per cylinder The flat twin cylinder 1948 Citron 2CV used one double ended coil without a distributor and just contact breakers in a wasted spark system

In modern systems the distributor is omitted and ignition is instead electronically controlled Much smaller coils are used with one coil for each spark plug or one coil serving two spark plugs for example two coils in a four cylinder engine or three coils in a six cylinder engine A large ignition coil puts out about 40 kV and a small one such as from a lawn mower puts out about 15 kV These coils may be remotely mounted or they may be placed on top of the spark plug coil on plug or Direct Ignition Where one coil serves two spark plugs in two cylinders it is through the wasted spark system In this arrangement the coil generates two sparks per cycle to both cylinders The fuel in the cylinder that is nearing the end of its compression stroke is ignited whereas the spark in its companion that is nearing the end of its exhaust stroke has no effect The wasted spark system is more reliable than a single coil system with a distributor and less expensive than coil on plug

Where coils are individually applied per cylinder they may all be contained in a single molded block with multiple high tension terminals This is commonly called a coil pack

A bad coil pack may cause a misfire bad fuel consumption or loss of power

This is a list of all red cards shown during FIFA World Cups that is the occasions when a player has been expelled from the game in a football World Cup Finals match not including qualifying matches As FIFA is the governing body of football official red cards are only noted when FIFA recognised that a player was expelled or sent off in a match

This list includes all dismissals since the first FIFA World Cup in 1930 The use of red and yellow cards to indicate dismissals and cautions is a more recent invention having been introduced at the 1970 tournament

The terms anno Domini AD and before Christ BC are used to label or number years in the Julian and Gregorian calendars The term anno Domini is Medieval Latin and means in the year of the Lord but is often presented using our Lord instead of the Lord taken from the full original phrase anno Domini nostri Jesu Christi which translates to in the year of our Lord Jesus Christ

This calendar era is based on the traditionally reckoned year of the conception or birth of Jesus of Nazareth with AD counting years from the start of this epoch and BC denoting years before the start of the era There is no year zero in this scheme so the year AD 1 immediately follows the year 1 BC This dating system was devised in 525 by Dionysius Exiguus of Scythia Minor but was not widely used until after 800

The Gregorian calendar is the most widely used calendar in the world today For decades it has been the unofficial global standard adopted in the pragmatic interests of international communication transportation and commercial integration and recognized by international institutions such as the United Nations

Traditionally English followed Latin usage by placing the AD abbreviation before the year number However BC is placed after the year number for example AD 2018 but 68 BC which also preserves syntactic order The abbreviation is also widely used after the number of a century or millennium as in fourth century AD or second millennium AD although conservative usage formerly rejected such expressions Because BC is the English abbreviation for Before Christ it is sometimes incorrectly concluded that AD means After Death ie after the death of Jesus However this would mean that the approximate 33 years commonly associated with the life of Jesus would neither be included in the BC nor the AD time scales

Terminology that is viewed by some as being more neutral and inclusive of nonChristian people is to call this the Current or Common Era abbreviated as CE with the preceding years referred to as Before the Common or Current Era BCE Astronomical year numbering and ISO 8601 avoid words or abbreviations related to Christianity but use the same numbers for AD years

The Anno Domini dating system was devised in 525 by Dionysius Exiguus to enumerate the years in his Easter table His system was to replace the Diocletian era that had been used in an old Easter table because he did not wish to continue the memory of a tyrant who persecuted Christians The last year of the old table Diocletian 247 was immediately followed by the first year of his table AD 532 When he devised his table Julian calendar years were identified by naming the consuls who held office that year he himself stated that the present year was the consulship of Probus Junior which was 525 years since the incarnation of our Lord Jesus Christ Thus Dionysius implied that Jesus incarnation occurred 525 years earlier without stating the specific year during which his birth or conception occurred However nowhere in his exposition of his table does Dionysius relate his epoch to any other dating system whether consulate Olympiad year of the world or regnal year of Augustus much less does he explain or justify the underlying date

Bonnie J Blackburn and Leofranc Holford Strevens briefly present arguments for 2 BC 1 BC or AD 1 as the year Dionysius intended for the Nativity or incarnation Among the sources of confusion are

It is not known how Dionysius established the year of Jesus s birth Two major theories are that Dionysius based his calculation on the Gospel of Luke which states that Jesus was about thirty years old shortly after the fifteenth year of the reign of Tiberius Caesar and hence subtracted thirty years from that date or that Dionysius counted back 532 years from the first year of his new table It is convenient to initiate a calendar not from the very day of an event but from the beginning of a cycle which occurs in close proximity For example the Islamic calendar begins not from the date of the Hijra but rather weeks prior on the first occurrence of the month of Muharram corresponding to 16 July 622

It has also been speculated by Georges Declercq that Dionysius desire to replace Diocletian years with a calendar based on the incarnation of Christ was intended to prevent people from believing the imminent end of the world At the time it was believed by some that the resurrection of the dead and end of the world would occur 500 years after the birth of Jesus The old Anno Mundi calendar theoretically commenced with the creation of the world based on information in the Old Testament It was believed that based on the Anno Mundi calendar Jesus was born in the year 5500 or 5500 years after the world was created with the year 6000 of the Anno Mundi calendar marking the end of the world Anno Mundi 6000 approximately AD 500 was thus equated with the resurrection and the end of the world but this date had already passed in the time of Dionysius

The Anglo Saxon historian the Venerable Bede who was familiar with the work of Dionysius Exiguus used Anno Domini dating in his Ecclesiastical History of the English People completed in 731 In this same history he also used another Latin term ante vero incarnationis dominicae tempus anno sexagesimo in fact in the 60th year before the time of the Lord s incarnation equivalent to the English before Christ to identify years before the first year of this era Both Dionysius and Bede regarded Anno Domini as beginning at the incarnation of Jesus but the distinction between Incarnation and Nativity was not drawn until the late 9th century when in some places the Incarnation epoch was identified with Christ s conception ie the Annunciation on March 25 Annunciation style

On the continent of Europe Anno Domini was introduced as the era of choice of the Carolingian Renaissance by the English cleric and scholar Alcuin in the late eighth century Its endorsement by Emperor Charlemagne and his successors popularizing the use of the epoch and spreading it throughout the Carolingian Empire ultimately lies at the core of the system s prevalence According to the Catholic Encyclopedia popes continued to date documents according to regnal years for some time but usage of AD gradually became more common in Roman Catholic countries from the 11th to the 14th centuries In 1422 Portugal became the last Western European country to switch to the system begun by Dionysius Eastern Orthodox countries only began to adopt AD instead of the Byzantine calendar in 1700 when Russia did so with others adopting it in the 19th and 20th centuries

Although Anno Domini was in widespread use by the 9th century the term Before Christ or its equivalent did not become common until much later Bede used the expression anno igitur ante incarnationem Dominicam so in the year before the incarnation of the Lord twice Anno an xpi nativitate in the year before the birth of Christ is found in 1474 in a work by a German monk In 1627 the French Jesuit theologian Denis Ptau Dionysius Petavius in Latin with his work De doctrina temporum popularized the usage ante Christum Latin for Before Christ to mark years prior to AD

When the reckoning from Jesus incarnation began replacing the previous dating systems in western Europe various people chose different Christian feast days to begin the year Christmas Annunciation or Easter Thus depending on the time and place the year number changed on different days in the year which created slightly different styles in chronology

With these various styles the same day could in some cases be dated in 1099 1100 or 1101

The date of birth of Jesus of Nazareth is not stated in the gospels or in any secular text but most scholars assume a date of birth between 6 BC and 4 BC The historical evidence is too fragmentary to allow a definitive dating but the date is estimated through two different approaches one by analyzing references to known historical events mentioned in the Nativity accounts in the Gospels of Luke and Matthew and the second by working backwards from the estimation of the start of the ministry of Jesus

During the first six centuries of what would come to be known as the Christian era European countries used various systems to count years Systems in use included consular dating imperial regnal year dating and Creation dating

Although the last nonimperial consul Basilius was appointed in 541 by Emperor Justinian I later emperors through Constans II 641 668 were appointed consuls on the first 1 January after their accession All of these emperors except Justinian used imperial postconsular years for the years of their reign along with their regnal years Long unused this practice was not formally abolished until Novell XCIV of the law code of Leo VI did so in 888

Another calculation had been developed by the Alexandrian monk Annianus around the year AD 400 placing the Annunciation on 25 March AD 9 Julian eight to ten years after the date that Dionysius was to imply Although this incarnation was popular during the early centuries of the Byzantine Empire years numbered from it an Era of Incarnation were exclusively used and are yet used in Ethiopia This accounts for the seven or eight year discrepancy between the Gregorian and Ethiopian calendars Byzantine chroniclers like Maximus the Confessor George Syncellus and Theophanes dated their years from Annianus creation of the world This era called Anno Mundi year of the world abbreviated AM by modern scholars began its first year on 25 March 5492 BC Later Byzantine chroniclers used Anno Mundi years from 1 September 5509 BC the Byzantine Era No single Anno Mundi epoch was dominant throughout the Christian world Eusebius of Caesarea in his Chronicle used an era beginning with the birth of Abraham dated in 2016 BC AD 1 2017 Anno Abrahami

Spain and Portugal continued to date by the Era of the Caesars or Spanish Era which began counting from 38 BC well into the Middle Ages In 1422 Portugal became the last Catholic country to adopt the Anno Domini system

The Era of Martyrs which numbered years from the accession of Diocletian in 284 who launched the last yet most severe persecution of Christians was used by the Church of Alexandria and is still used officially by the Coptic Orthodox and Coptic Catholic churches It was also used by the Ethiopian church Another system was to date from the crucifixion of Jesus which as early as Hippolytus and Tertullian was believed to have occurred in the consulate of the Gemini AD 29 which appears in some medieval manuscripts

Alternative names for the Anno Domini era include vulgaris aerae found 1615 in Latin Vulgar Era in English as early as 1635 Christian Era in English in 1652 Common Era in English 1708 and Current Era Since 1856 the alternative abbreviations CE and BCE sometimes written CE and BCE are sometimes used in place of AD and BC

The Common Current Era CE terminology is often preferred by those who desire a term that does not explicitly make religious references For example Cunningham and Starr 1998 write that BCE CE do not presuppose faith in Christ and hence are more appropriate for interfaith dialog than the conventional BC AD Upon its foundation the Republic of China adopted the Minguo Era but used the Western calendar for international purposes The translated term was x yun Western Era Later in 1949 the People s Republic of China adopted gngyun Common Era for all purposes domestic and foreign

In the AD year numbering system whether applied to the Julian or Gregorian calendars AD 1 is preceded by 1 BC There is no year 0 between them so a new century begins in a year which has 01 as the final digits eg 1801 1901 2001 New millennia likewise are considered to have begun in 1001 and 2001 This is at odds with the much more common conception that centuries and millennia begin when the trailing digits are zeroes 1800 1900 2000 etc for example the worldwide celebration of the new millennium took place on New Year s Eve 1999 when the year number ticked over to 2000

For computational reasons astronomical year numbering and the ISO 8601 standard designate years so that AD 1 year 1 1 BC year 0 2 BC year 1 etc In common usage ancient dates are expressed in the Julian calendar but ISO 8601 uses the Gregorian calendar and astronomers may use a variety of time scales depending on the application Thus dates using the year 0 or negative years may require further investigation before being converted to BC or AD

The abundance of elements in Earth s crust is shown in tabulated form with the estimated crustal abundance for each chemical element shown as either percentage or parts per million ppm by mass 10000 ppm 1

Price controls are governmental restrictions on the prices that can be charged for goods and services in a market The intent behind implementing such controls can stem from the desire to maintain affordability of goods to prevent during shortages and to slow inflation or alternatively to ensure a minimum income for providers of certain goods or a minimum wage There are two primary forms of price control a price ceiling the maximum price that can be charged and a price floor the minimum price that can be charged

Historically price controls have often been imposed as part of a larger incomes policy package also employing wage controls and other regulatory elements

Although price controls are sometimes used by governments economists usually agree that price controls do nt accomplish what they are intended to do and are generally to be avoided For example nearly three quarters of economists surveyed disagreed with the statement Wage price controls are a useful policy option in the control of inflation

The Roman Emperor Diocletian tried to set maximum prices for all commodities in the late 3rd century AD but with little success

During the French Revolution the Law of the Maximum set price limits on the sale of food and other staples

Governments in planned economies typically control prices on most or all goods but have not sustained high economic performance and have been almost entirely replaced by mixed economies

Price controls have also been used in modern times in less planned economies such as rent control

During World War I the United States Food Administration enforced price controls on food Price controls were also imposed in the US and Nazi Germany during World War II

Wage controls have been tried in many countries to reduce inflation seldom successfully Modern neoclassical economic theory supports the alternative remedy of reducing the money supply and proposes that monetary inflation is caused by too much money creation by the central bank

The National Board for Prices and Incomes was created by the government of Harold Wilson in 1965 in an attempt to solve the problem of inflation in the British economy by managing wages and prices The Prices and Incomes Act 1966 c 33 affected UK labour law regarding wage levels and price policies It allowed the government to begin a process to scrutinise rising levels of wages then around 8 per year by initiating reports and inquiries and ultimately giving orders for a standstill The objective was to control inflation It proved unpopular after the 1960s

States have sometimes chosen to implement their own control policies California controls the prices of electricity within the state which conservative economist Thomas Sowell blames for the occasional electricity shortages the state experiences Sowell said in 2001 Since the utility companies have been paying more for electricity than they were allowed to charge their customers they were operating in the red and the financial markets are downgrading their bonds California s price setting board agreed to raise rates but not as much as the companies were paying on the wholesale market for their electricity Economist Lawrence Makovich contended We ve already seen in California that price caps on retail rates increased demand and made the shortage worse and price caps also forced the largest utility Pacific Gas and Electric into bankruptcy in four months While some charged that electricity providers had in past years charged above market rates in 2002 the San Francisco Chronicle reported that before the blackouts many energy providers left the state because they could make a greater profit in other Western states The Federal Energy Regulatory Commission stepped in and set price caps for each megawatt of power bought after lifting the caps to avoid rolling blackouts six months previously

The state of Hawaii briefly introduced a cap on the wholesale price of gasoline the Gas Cap Law in an effort to fight price gouging in that state in 2005 Because it was widely seen as too soft and ineffective it was repealed shortly thereafter

The primary criticism leveled against price controls is that by keeping prices artificially low demand is increased to the point where supply can not keep up leading to shortages in the price controlled product For example Lactantius wrote that Diocletian by various taxes he had made all things exceedingly expensive attempted by a law to limit their prices Then much blood of merchants was shed for trifles men were afraid to offer anything for sale and the scarcity became more excessive and grievous than ever Until in the end the price limit law after having proved destructive to many people was from mere necessity abolished As with Diocletian s Edict on Maximum Prices shortages lead to black markets where prices for the same good exceed those of an uncontrolled market Furthermore once controls are removed prices will immediately increase which can temporarily shock the economic system

A classic example of how price controls cause shortages was during the Arab oil embargo between October 19 1973 and March 17 1974 Long lines of cars and trucks quickly appeared at retail gas stations in the US and some stations closed because of a shortage of fuel at the low price set by the US Cost of Living Council The fixed price was below what the market would otherwise bear and as a result the inventory disappeared It made no difference whether prices were voluntarily or involuntarily posted below the market clearing price Scarcity resulted in either case Price controls fail to achieve their proximate aim which is to reduce prices paid by retail consumers but such controls do manage to reduce supply

Nobel prize winner Milton Friedman said We economists do nt know much but we do know how to create a shortage If you want to create a shortage of tomatoes for example just pass a law that retailers ca nt sell tomatoes for more than two cents per pound Instantly you ll have a tomato shortage It s the same with oil or gas

US President Richard Nixon s Secretary of the Treasury George Shultz enacting Nixon s New Economic Policy lifted price controls that had begun in 1971 part of the Nixon Shock This lifting of price controls resulted in a rapid increase in prices Price freezes were reestablished five months later Stagflation was eventually ended in the United States when the Federal Reserve under chairman Paul Volcker raised interest rates to unusually high levels This successfully ended high inflation but caused a recession that ended in the early 1980s

Timeline of Kentucky history

C dynamic memory allocation refers to performing manual memory management for dynamic memory allocation in the C programming language via a group of functions in the C standard library namely malloc realloc calloc and free

The C programming language includes these functions for compatibility with C however the operators new and delete provide similar functionality and are recommended by that language s authors

Many different implementations of the actual memory allocation mechanism used by malloc are available Their performance varies in both execution time and required memory

The C programming language manages memory statically automatically or dynamically Static duration variables are allocated in main memory usually along with the executable code of the program and persist for the lifetime of the program automatic duration variables are allocated on the stack and come and go as functions are called and return For static duration and automatic duration variables the size of the allocation must be compile time constant except for the case of variable length automatic arrays If the required size is not known until run time for example if data of arbitrary size is being read from the user or from a disk file then using fixed size data objects is inadequate

The lifetime of allocated memory can also cause concern Neither static nor automatic duration memory is adequate for all situations Automatic allocated data can not persist across multiple function calls while static data persists for the life of the program whether it is needed or not In many situations the programmer requires greater flexibility in managing the lifetime of allocated memory

These limitations are avoided by using dynamic memory allocation in which memory is more explicitly but more flexibly managed typically by allocating it from the free store informally called the heap an area of memory structured for this purpose In C the library function malloc is used to allocate a block of memory on the heap The program accesses this block of memory via a pointer that malloc returns When the memory is no longer needed the pointer is passed to free which deallocates the memory so that it can be used for other purposes

Some platforms provide library calls which allow run time dynamic allocation from the C stack rather than the heap eg alloca This memory is automatically freed when the calling function ends

The C dynamic memory allocation functions are defined in stdlib h header cstdlib header in C

Creating an array of ten integers with automatic scope is straightforward in C

However the size of the array is fixed at compile time If one wishes to allocate a similar array dynamically the following code can be used

This computes the number of bytes that ten integers occupy in memory then requests that many bytes from malloc and assigns the result to a pointer named array due to C syntax pointers and arrays can be used interchangeably in some situations

Because malloc might not be able to service the request it might return a null pointer and it is good programming practice to check for this

When the program no longer needs the dynamic array it must eventually call free to return the memory it occupies to the free store

The memory set aside by malloc is not initialized and may contain cruft the remnants of previously used and discarded data After allocation with malloc elements of the array are uninitialized variables The command calloc will return an allocation that has already been cleared

With realloc we can resize the amount of memory a pointer points to For example if we have a pointer acting as an array of size n displaystyle n and we want to change it to an array of size m displaystyle m we can use realloc

Note that realloc must be assumed to have changed the base address of the block ie if it has failed to extend the size of the original block and has therefore allocated a new larger block elsewhere and copied the old contents into it Therefore any pointers to addresses within the original block are also no longer valid

malloc returns a void pointer void which indicates that it is a pointer to a region of unknown data type The use of casting is required in C due to the strong type system whereas this is not the case in C The lack of a specific pointer type returned from malloc is type unsafe behaviour according to some programmers malloc allocates based on byte count but not on type This is different from the C new operator that returns a pointer whose type relies on the operand See C Type Safety

One may cast see type conversion this pointer to a specific type

There are advantages and disadvantages to performing such a cast

The improper use of dynamic memory allocation can frequently be a source of bugs These can include security bugs or program crashes most often due to segmentation faults

Most common errors are as follows

The implementation of memory management depends greatly upon operating system and architecture Some operating systems supply an allocator for malloc while others supply functions to control certain regions of data The same dynamic memory allocator is often used to implement both malloc and the operator new in C

Implementation of the allocator is commonly done using the heap or data segment The allocator will usually expand and contract the heap to fulfill allocation requests

The heap method suffers from a few inherent flaws stemming entirely from fragmentation Like any method of memory allocation the heap will become fragmented that is there will be sections of used and unused memory in the allocated space on the heap A good allocator will attempt to find an unused area of already allocated memory to use before resorting to expanding the heap The major problem with this method is that the heap has only two significant attributes base or the beginning of the heap in virtual memory space and length or its size The heap requires enough system memory to fill its entire length and its base can never change Thus any large areas of unused memory are wasted The heap can get stuck in this position if a small used segment exists at the end of the heap which could waste any amount of address space On lazy memory allocation schemes such as those often found in the Linux operating system a large heap does not necessarily reserve the equivalent system memory it will only do so at the first write time reads of nonmapped memory pages return zero The granularity of this depends on page size

Doug Lea has developed dlmalloc Doug Lea s Malloc as a general purpose allocator starting in 1987 The GNU C library glibc uses ptmalloc an allocator based on dlmalloc

Memory on the heap is allocated as chunks an 8 byte aligned data structure which contains a header and usable memory Allocated memory contains an 8 or 16 byte overhead for the size of the chunk and usage flags Unallocated chunks also store pointers to other free chunks in the usable space area making the minimum chunk size 24 bytes

Unallocated memory is grouped into bins of similar sizes implemented by using a double linked list of chunks with pointers stored in the unallocated space inside the chunk

For requests below 256 bytes a smallbin request a simple two power best fit allocator is used If there are no free blocks in that bin a block from the next highest bin is split in two

For requests of 256 bytes or above but below the mmap threshold recent versions of dlmalloc use an in place bitwise trie algorithm If there is no free space left to satisfy the request dlmalloc tries to increase the size of the heap usually via the brk system call

For requests above the mmap threshold a largebin request the memory is always allocated using the mmap system call The threshold is usually 256 KB The mmap method averts problems with huge buffers trapping a small allocation at the end after their expiration but always allocates an entire page of memory which on many architectures is 4096 bytes in size

Since FreeBSD 70 and NetBSD 50 the old malloc implementation phkmalloc was replaced by jemalloc written by Jason Evans The main reason for this was a lack of scalability of phkmalloc in terms of multithreading In order to avoid lock contention jemalloc uses separate arenas for each CPU Experiments measuring number of allocations per second in multithreading application have shown that this makes it scale linearly with the number of threads while for both phkmalloc and dlmalloc performance was inversely proportional to the number of threads