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avy lift-class Saturn launch vehicles, which would be required for Apollo.
=== Manned Spacecraft Center ===
It became clear that managing the Apollo program would exceed the capabilities of Robert R. Gilruth's Space Task Group, which had been directing the nation's crewed space program from NASA's Langley Research C... | https://en.wikipedia.org/wiki/Apollo_program |
and construction of the MSC facility was under way, Kennedy visited Rice to reiterate his challenge in a famous speech:
But why, some say, the Moon? Why choose this as our goal? And they may well ask, why climb the highest mountain? Why, 35 years ago, fly the Atlantic? ...
We choose to go to the Moon. We choose to go... | https://en.wikipedia.org/wiki/Apollo_program |
already being built for the Saturn I and IB rockets at the northernmost end: LC-34 and LC-37. But an even bigger facility would be needed for the mammoth rocket required for the crewed lunar mission, so land acquisition was started in July 1961 for a Launch Operations Center (LOC) immediately north of Canaveral at Mer... | https://en.wikipedia.org/wiki/Apollo_program |
launcher platform and then moved by a crawler-transporter to one of several launch pads. Although at least three pads were planned, only two, designated A and B, were completed in October 1965. The LOC also included an Operations and Checkout Building (OCB) to which Gemini and Apollo spacecraft were initially received ... | https://en.wikipedia.org/wiki/Apollo_program |
uty Administrator) Seamans to reorganize the Office of Manned Space Flight (OMSF). On July 23, 1963, Webb announced Mueller's appointment as Deputy Associate Administrator for Manned Space Flight, to replace then Associate Administrator D. Brainerd Holmes on his retirement effective September 1. Under Webb's reorganiza... | https://en.wikipedia.org/wiki/Apollo_program |
im, on the condition that Phillips be made Apollo Program Director. Mueller agreed, and Phillips managed Apollo from January 1964, until it achieved the first human landing in July 1969, after which he returned to Air Force duty.
Charles Fishman, in One Giant Leap, estimated the number of people and organizations invol... | https://en.wikipedia.org/wiki/Apollo_program |
n ship would land all three astronauts atop a 113,000-pound (51,000 kg) descent propulsion stage, which would be left on the Moon. This design would have required development of the extremely powerful Saturn C-8 or Nova launch vehicle to carry a 163,000-pound (74,000 kg) payload to the Moon.
Earth Orbit Rendezvous (EOR... | https://en.wikipedia.org/wiki/Apollo_program |
eved the goal with Apollo 11 on July 20, 1969: a single Saturn V launched a 96,886-pound (43,947 kg) spacecraft that was composed of a 63,608-pound (28,852 kg) Apollo command and service module which remained in orbit around the Moon and a 33,278-pound (15,095 kg) two-stage Apollo Lunar Module spacecraft which was flow... | https://en.wikipedia.org/wiki/Apollo_program |
s including John Houbolt at Langley Research Center emphasized the important weight reductions that were offered by the LOR approach. Throughout 1960 and 1961, Houbolt campaigned for the recognition of LOR as a viable and practical option. Bypassing the NASA hierarchy, he sent a series of memos and reports on the issue... | https://en.wikipedia.org/wiki/Apollo_program |
s Houbolt's ceaseless work—played an important role in publicizing the workability of the approach. In late 1961 and early 1962, members of the Manned Spacecraft Center began to come around to support LOR, including the newly hired deputy director of the Office of Manned Space Flight, Joseph Shea, who became a champion... | https://en.wikipedia.org/wiki/Apollo_program |
o second-guess NASA's decisions on the Saturn V launch vehicle and LOR by forcing Shea, Seamans, and even Webb to defend themselves, delaying its formal announcement to the press on July 11, 1962, and forcing Webb to still hedge the decision as "tentative".
Wiesner kept up the pressure, even making the disagreement pub... | https://en.wikipedia.org/wiki/Apollo_program |
for Webb. NASA announced the selection of Grumman as the LEM contractor in November 1962.
Space historian James Hansen concludes that:
Without NASA's adoption of this stubbornly held minority opinion in 1962, the United States may still have reached the Moon, but almost certainly it would not have been accomplished b... | https://en.wikipedia.org/wiki/Apollo_program |
cal power and life support to get the crew home safely.
== Spacecraft ==
Faget's preliminary Apollo design employed a cone-shaped command module, supported by one of several service modules providing propulsion and electrical power, sized appropriately for the space station, cislunar, and lunar landing missions. Onc... | https://en.wikipedia.org/wiki/Apollo_program |
service module ===
The command module (CM) was the conical crew cabin, designed to carry three astronauts from launch to lunar orbit and back to an Earth ocean landing. It was the only component of the Apollo spacecraft to survive without major configuration changes as the program evolved from the early Apollo study d... | https://en.wikipedia.org/wiki/Apollo_program |
ance communications on the lunar flights. On the extended lunar missions, an orbital scientific instrument package was carried. The service module was discarded just before reentry. The module was 24.6 feet (7.5 m) long and 12.83 feet (3.91 m) in diameter. The initial lunar flight version weighed approximately 51,300 p... | https://en.wikipedia.org/wiki/Apollo_program |
ed that the initial design should be continued as Block I which would be used for early testing, while Block II, the actual lunar spacecraft, would incorporate the docking equipment and take advantage of the lessons learned in Block I development.
=== Apollo Lunar Module ===
The Apollo Lunar Module (LM) was designed... | https://en.wikipedia.org/wiki/Apollo_program |
M model weighed approximately 33,300 pounds (15,100 kg), and allowed surface stays up to around 34 hours. An extended lunar module (ELM) weighed over 36,200 pounds (16,400 kg), and allowed surface stays of more than three days. The contract for design and construction of the lunar module was awarded to Grumman Aircraft... | https://en.wikipedia.org/wiki/Apollo_program |
th a lunar payload capability of over 180,000 pounds (82,000 kg). The June 11, 1962, decision to use lunar orbit rendezvous enabled the Saturn V to replace the Nova, and the MSFC proceeded to develop the Saturn rocket family for Apollo.
Since Apollo, like Mercury, used more than one launch vehicle for space missions, N... | https://en.wikipedia.org/wiki/Apollo_program |
as built by General Dynamics/Convair. After an August 1963 qualification test flight, four LES test flights (A-001 through 004) were made at the White Sands Missile Range between May 1964 and January 1966.
=== Saturn I ===
Saturn I, the first US heavy lift launch vehicle, was initially planned to launch partially eq... | https://en.wikipedia.org/wiki/Apollo_program |
boilerplate CSMs (designated AS-101 through AS-105) into orbit in 1964 and 1965. The last three of these further supported the Apollo program by also carrying Pegasus satellites, which verified the safety of the translunar environment by measuring the frequency and severity of micrometeorite impacts.
In September 1962... | https://en.wikipedia.org/wiki/Apollo_program |
ydrogen fuel with LOX, to produce 200,000 pounds-force (890 kN) of thrust. A restartable version of the S-IVB was used as the third stage of the Saturn V. The Saturn IB could send over 40,000 pounds (18,100 kg) into low Earth orbit, sufficient for a partially fueled CSM or the LM. Saturn IB launch vehicles and flights ... | https://en.wikipedia.org/wiki/Apollo_program |
burned RP-1/LOX for a rated thrust of 7,500,000 pounds-force (33,400 kN), which was upgraded to 7,610,000 pounds-force (33,900 kN). The second and third stages burned liquid hydrogen; the third stage was a modified version of the S-IVB, with thrust increased to 230,000 pounds-force (1,020 kN) and capability to restart ... | https://en.wikipedia.org/wiki/Apollo_program |
one of them returned to it after landing once. One of the moonwalkers was a trained geologist. Of the 32, Gus Grissom, Ed White, and Roger Chaffee were killed during a ground test in preparation for the Apollo 1 mission.
The Apollo astronauts were chosen from the Project Mercury and Gemini veterans, plus from two late... | https://en.wikipedia.org/wiki/Apollo_program |
, ability, or courage", and personal "contribution representing substantial progress to the NASA mission". The medals were awarded posthumously to Grissom, White, and Chaffee in 1969, then to the crews of all missions from Apollo 8 onward. The crew that flew the first Earth orbital test mission Apollo 7, Walter M. Schi... | https://en.wikipedia.org/wiki/Apollo_program |
rofile variations ===
The first three lunar missions (Apollo 8, Apollo 10, and Apollo 11) used a free return trajectory, keeping a flight path coplanar with the lunar orbit, which would allow a return to Earth in case the SM engine failed to make lunar orbit insertion. Landing site lighting conditions on later mission... | https://en.wikipedia.org/wiki/Apollo_program |
d subsequent missions were deliberately crashed on the Moon instead of being sent to solar orbit.
Starting with Apollo 13, descent orbit insertion was to be performed using the service module engine instead of the LM engine, in order to allow a greater fuel reserve for landing. This was actually done for the first time... | https://en.wikipedia.org/wiki/Apollo_program |
command module heat shield.
A third Saturn IB test, AS-203 launched from pad 37, went into orbit to support design of the S-IVB upper stage restart capability needed for the Saturn V. It carried a nose cone instead of the Apollo spacecraft, and its payload was the unburned liquid hydrogen fuel, the behavior of which e... | https://en.wikipedia.org/wiki/Apollo_program |
the first Block II CSM and LM in a dual mission known as AS-207/208, or AS-278 (each spacecraft would be launched on a separate Saturn IB). The Block II crew positions were titled Commander, Command Module Pilot, and Lunar Module Pilot. The astronauts would begin wearing a new Apollo A6L spacesuit, designed to accommod... | https://en.wikipedia.org/wiki/Apollo_program |
with Chaffee. NASA announced the final crew selection for AS-204 on March 21, 1966, with the backup crew consisting of Gemini veterans James McDivitt and David Scott, with rookie Russell L. "Rusty" Schweickart. Mercury/Gemini veteran Wally Schirra, Eisele, and rookie Walter Cunningham were announced on September 29 as ... | https://en.wikipedia.org/wiki/Apollo_program |
elivered by North American Aviation to the Kennedy Space Center with long lists of equipment problems which had to be corrected before flight; these delays caused the launch of AS-202 to slip behind AS-203, and eliminated hopes the first crewed mission might be ready to launch as soon as November 1966, concurrently wit... | https://en.wikipedia.org/wiki/Apollo_program |
American's problems and identify corrections. Phillips documented his findings in a December 19 letter to NAA president Lee Atwood, with a strongly worded letter by Mueller, and also gave a presentation of the results to Mueller and Deputy Administrator Robert Seamans. Meanwhile, Grumman was also encountering problems... | https://en.wikipedia.org/wiki/Apollo_program |
tdown simulation test closer to the February 21 launch, with both spacecraft and launch vehicle fueled.
The plugs-out test began on the morning of January 27, 1967, and immediately was plagued with problems. First, the crew noticed a strange odor in their spacesuits which delayed the sealing of the hatch. Then, communi... | https://en.wikipedia.org/wiki/Apollo_program |
at "deficiencies existed in command module design, workmanship and quality control". At the insistence of NASA Administrator Webb, North American removed Harrison Storms as command module program manager. Webb also reassigned Apollo Spacecraft Program Office (ASPO) Manager Joseph Francis Shea, replacing him with George... | https://en.wikipedia.org/wiki/Apollo_program |
be designated by the Block II titles, regardless of whether a LM was present on the flight or not.
==== Uncrewed Saturn V and LM tests ====
On April 24, 1967, Mueller published an official Apollo mission numbering scheme, using sequential numbers for all flights, crewed or uncrewed. The sequence would start with Apol... | https://en.wikipedia.org/wiki/Apollo_program |
sing the Saturn IB; D was the first crewed CSM/LM flight (this replaced AS-258, using a single Saturn V launch); E would be a higher Earth orbit CSM/LM flight; F would be the first lunar mission, testing the LM in lunar orbit but without landing (a "dress rehearsal"); and G would be the first crewed landing. The list o... | https://en.wikipedia.org/wiki/Apollo_program |
ght of the LM in Earth orbit, launched from pad 37 on January 22, 1968, by the Saturn IB that would have been used for Apollo 1. The LM engines were successfully test-fired and restarted, despite a computer programming error which cut short the first descent stage firing. The ascent engine was fired in abort mode, know... | https://en.wikipedia.org/wiki/Apollo_program |
cond and third stages. Two S-II engines shut down prematurely, but the remaining engines were able to compensate. The damage to the third stage engine was more severe, preventing it from restarting for trans-lunar injection. Mission controllers were able to use the service module engine to essentially repeat the flight... | https://en.wikipedia.org/wiki/Apollo_program |
uld not be ready in time. Rather than waste the Saturn V on another simple Earth-orbiting mission, ASPO Manager George Low suggested the bold step of sending Apollo 8 to orbit the Moon instead, deferring the D mission to the next mission in March 1969, and eliminating the E mission. This would keep the program on track... | https://en.wikipedia.org/wiki/Apollo_program |
Earth orbit on Apollo 9, and Schweickart tested the full lunar EVA suit with its portable life support system (PLSS) outside the LM. The F mission was successfully carried out on Apollo 10 in May 1969 by Gemini veterans Thomas P. Stafford, John Young and Eugene Cernan. Stafford and Cernan took the LM to within 50,000 ... | https://en.wikipedia.org/wiki/Apollo_program |
y 24.
That's one small step for [a] man, one giant leap for mankind.
=== Production lunar landings ===
In November 1969, Charles "Pete" Conrad became the third person to step onto the Moon, which he did while speaking more informally than had Armstrong:
Whoopee! Man, that may have been a small one for Neil, but tha... | https://en.wikipedia.org/wiki/Apollo_program |
nding missions through Apollo 20. Shortly after Apollo 11, NASA publicized a preliminary list of eight more planned landing sites after Apollo 12, with plans to increase the mass of the CSM and LM for the last five missions, along with the payload capacity of the Saturn V. These final missions would combine the I and J... | https://en.wikipedia.org/wiki/Apollo_program |
ll, Jack Swigert, and Fred Haise in April 1970, headed for the Fra Mauro formation. But two days out, a liquid oxygen tank exploded, disabling the service module and forcing the crew to use the LM as a "lifeboat" to return to Earth. Another NASA review board was convened to determine the cause, which turned out to be a... | https://en.wikipedia.org/wiki/Apollo_program |
ng, and NASA also had to make funds available for the development of the upcoming Space Shuttle. By 1971, the decision was made to also cancel missions 18 and 19. The two unused Saturn Vs became museum exhibits at the John F. Kennedy Space Center on Merritt Island, Florida, George C. Marshall Space Center in Huntsville... | https://en.wikipedia.org/wiki/Apollo_program |
Edgar Mitchell. This time the mission was successful. Shepard and Mitchell spent 33 hours and 31 minutes on the surface, and completed two EVAs totalling 9 hours 24 minutes, which was a record for the longest EVA by a lunar crew at the time.
In August 1971, just after conclusion of the Apollo 15 mission, President Ric... | https://en.wikipedia.org/wiki/Apollo_program |
d by John Young, with Ken Mattingly and Charles Duke. Young and Duke spent just under three days on the surface, with a total of over 20 hours EVA.
Apollo 17 was the last of the Apollo program, landing in the Taurus–Littrow region in December 1972. Eugene Cernan commanded Ronald E. Evans and NASA's first scientist-astr... | https://en.wikipedia.org/wiki/Apollo_program |
ouston. Today, 75% of the samples are stored at the Lunar Sample Laboratory Facility built in 1979.
The rocks collected from the Moon are extremely old compared to rocks found on Earth, as measured by radiometric dating techniques. They range in age from about 3.2 billion years for the basaltic samples derived from the... | https://en.wikipedia.org/wiki/Apollo_program |
strial counterpart. KREEP and the anorthositic samples have been used to infer that the outer portion of the Moon was once completely molten (see lunar magma ocean).
Almost all the rocks show evidence of impact process effects. Many samples appear to be pitted with micrometeoroid impact craters, which is never seen on ... | https://en.wikipedia.org/wiki/Apollo_program |
this amount, $20.2 billion ($145 billion adjusted) was spent on the design, development, and production of the Saturn family of launch vehicles, the Apollo spacecraft, spacesuits, scientific experiments, and mission operations. The cost of constructing and operating Apollo-related ground facilities, such as the NASA h... | https://en.wikipedia.org/wiki/Apollo_program |
llion for a crewed lunar landing effort. NASA Administrator James Webb increased this estimate to $20 billion before reporting it to Vice President Johnson in April 1961.
Project Apollo was a massive undertaking, representing the largest research and development project in peacetime. At its peak, it employed over 400,0... | https://en.wikipedia.org/wiki/Apollo_program |
e Apollo Extension Series (Apollo X) proposed up to 30 flights to Earth orbit, using the space in the Spacecraft Lunar Module Adapter (SLA) to house a small orbital laboratory (workshop). Astronauts would continue to use the CSM as a ferry to the station. This study was followed by design of a larger orbital workshop t... | https://en.wikipedia.org/wiki/Apollo_program |
scope Mount. Skylab's last crew departed the station on February 8, 1974, and the station itself re-entered the atmosphere in 1979 after development of the Space Shuttle was delayed too long to save it.
The Apollo–Soyuz program also used Apollo hardware for the first joint nation spaceflight, paving the way for future ... | https://en.wikipedia.org/wiki/Apollo_program |
l be standing, with the exception of the one left during the Apollo 11 mission, which was blown over during that mission's lift-off from the lunar surface; the degree to which these flags retain their original colors remains unknown. The flags cannot be seen through a telescope from Earth.
In a November 16, 2009, edito... | https://en.wikipedia.org/wiki/Apollo_program |
photograph like this one is as close as we're able to come to looking directly back into the human past ...
There the [Apollo 11] lunar module sits, parked just where it landed 40 years ago, as if it still really were 40 years ago and all the time since merely imaginary.
== Legacy ==
=== Science and engineering ===... | https://en.wikipedia.org/wiki/Apollo_program |
ction of ICs. The crucial difference between the requirements of Apollo and the missile programs was Apollo's much greater need for reliability. While the Navy and Air Force could work around reliability problems by deploying more missiles, the political and financial cost of failure of an Apollo mission was unacceptab... | https://en.wikipedia.org/wiki/Apollo_program |
e population of the world saw—either live or delayed—the Christmas Eve transmission during the ninth orbit of the Moon, and an estimated one-fifth of the population of the world watched the live transmission of the Apollo 11 moonwalk.
The Apollo program also affected environmental activism in the 1970s due to photos ta... | https://en.wikipedia.org/wiki/Apollo_program |
n noted the irony that in order to achieve the goal, the program required the organization of tremendous public resources within a vast, centralized government bureaucracy.
=== Apollo 11 broadcast data restoration project ===
Prior to Apollo 11's 40th anniversary in 2009, NASA searched for the original videotapes of... | https://en.wikipedia.org/wiki/Apollo_program |
3 (2012), Science Fiction/Comedy movie. Agent J played by Will Smith goes back to the Apollo 11 launch in 1969 to ensure that a global protection system is launched in to space.
For All Mankind (2019), TV series depicting an alternate history in which the Soviet Union was the first country to successfully land a man on... | https://en.wikipedia.org/wiki/Apollo_program |
Space Museum
Apollo 35th Anniversary Interactive Feature at NASA (in Flash)
Lunar Mission Timeline at the Lunar and Planetary Institute
Apollo Collection, The University of Alabama in Huntsville Archives and Special Collections
=== NASA reports ===
Apollo Program Summary Report (PDF), NASA, JSC-09423, April 1975
NASA... | https://en.wikipedia.org/wiki/Apollo_program |
f Apollo images, videos, and audio recordings
The Project Apollo Archive on Flickr
Apollo Image Atlas—almost 25,000 lunar images, Lunar and Planetary Institute
The short film The Time of Apollo (1975) is available for free viewing and download at the Internet Archive.
The short film The Time of Apollo (1975) is availab... | https://en.wikipedia.org/wiki/Apollo_program |
Radio programming is the process of organising a schedule of radio content for commercial broadcasting and public broadcasting by radio stations.
== History ==
The original inventors of radio, from Guglielmo Marconi's time on, expected it to be used for one-on-one wireless communication tasks where telephones and tel... | https://en.wikipedia.org/wiki/Radio_programming |
osed to narrowcasting) business organizations began to be called network affiliates, because they consisted of loose chains of individual stations located in various cities, all transmitting the standard overall-system supplied fare, often at synchronised agreed-upon times. Some of these radio network stations were own... | https://en.wikipedia.org/wiki/Radio_programming |
veloped late in the 20th century in both television and radio, where small slices of time were sold to many sponsors and no corporation claimed or wanted sponsorship of the entire show, except in rare cases. These later commercials also filled a much larger portion of the total program time than they had in the earlier... | https://en.wikipedia.org/wiki/Radio_programming |
television programming eroded the popularity of radio comedy, drama and variety shows. By the late 1950s, radio broadcasting took on much the form it has today – strongly focused on music, talk, news and sports, though drama can still be heard, especially on the BBC.
== References == | https://en.wikipedia.org/wiki/Radio_programming |
A property, in some object-oriented programming languages, is a special sort of class member, intermediate in functionality between a field (or data member) and a method. The syntax for reading and writing of properties is like for fields, but property reads and writes are (usually) translated to 'getter' and 'setter' ... | https://en.wikipedia.org/wiki/Property_(programming) |
ator methods instead.
Oberon-2 provides an alternative mechanism using object variable visibility flags.
Other languages designed for the Java Virtual Machine, such as Groovy, natively support properties.
While C++ does not have first class properties, they can be emulated with operator overloading.
Also note that some... | https://en.wikipedia.org/wiki/Property_(programming) |
ither returns or changes the underlying data, depending on the context of its invocation. Such techniques are used e.g. in Perl.
Some languages (Ruby, Smalltalk) achieve property-like syntax using normal methods, sometimes with a limited amount of syntactic sugar.
== Syntax variants ==
Some languages follow well-est... | https://en.wikipedia.org/wiki/Property_(programming) |
lass properties, but there exist several ways to emulate properties to a limited degree. Two of which follow:
==== Using Standard C++ ====
Also see Stack Overflow for a more detailed example.
==== C++, Microsoft, GCC, LLVM/clang and C++Builder-specific ====
An example taken from the MSDN documentation page.
=== ... | https://en.wikipedia.org/wiki/Property_(programming) |
===
Ruby also provides automatic getter/setter synthesizers defined as instance methods of Class.
=== Visual Basic ===
==== Visual Basic (.NET 2003–2010) ====
==== Visual Basic (only .NET 2010) ====
==== Visual Basic 6 ====
== See also ==
Attribute (computing)
Bound property
Field (computer science)
Indexer... | https://en.wikipedia.org/wiki/Property_(programming) |
In computer programming, assembly language (alternatively assembler language or symbolic machine code), often referred to simply as assembly and commonly abbreviated as ASM or asm, is any low-level programming language with a very strong correspondence between the instructions in the language and the architecture's ma... | https://en.wikipedia.org/wiki/Assembly_language |
rograms for an Electronic Digital Computer, who, however, used the term to mean "a program that assembles another program consisting of several sections into a single program". The conversion process is referred to as assembly, as in assembling the source code. The computational step when an assembler is processing a p... | https://en.wikipedia.org/wiki/Assembly_language |
n contrast to assembly languages, most high-level programming languages are generally portable across multiple architectures but require interpreting or compiling, much more complicated tasks than assembling.
In the first decades of computing, it was commonplace for both systems programming and application programming ... | https://en.wikipedia.org/wiki/Assembly_language |
y, it is typical to use small amounts of assembly language code within larger systems implemented in a higher-level language, for performance reasons or to interact directly with hardware in ways unsupported by the higher-level language. For instance, just under 2% of version 4.9 of the Linux kernel source code is wri... | https://en.wikipedia.org/wiki/Assembly_language |
e much more readable than machine code. Depending on the architecture, these elements may also be combined for specific instructions or addressing modes using offsets or other data as well as fixed addresses. Many assemblers offer additional mechanisms to facilitate program development, to control the assembly process,... | https://en.wikipedia.org/wiki/Assembly_language |
e, and that name can be used to insert the expanded text into other code.
Open code refers to any assembler input outside of a macro definition.
A cross assembler (see also cross compiler) is an assembler that is run on a computer or operating system (the host system) of a different type from the system on which the re... | https://en.wikipedia.org/wiki/Assembly_language |
program that provides language abstractions more often associated with high-level languages, such as advanced control structures (IF/THEN/ELSE, DO CASE, etc.) and high-level abstract data types, including structures/records, unions, classes, and sets.
A microassembler is a program that helps prepare a microprogram to ... | https://en.wikipedia.org/wiki/Assembly_language |
is most often used in systems programs which need direct access to the hardware.
== Key concepts ==
=== Assembler ===
An assembler program creates object code by translating combinations of mnemonics and syntax for operations and addressing modes into their numerical equivalents. This representation typically incl... | https://en.wikipedia.org/wiki/Assembly_language |
ne concrete example of this may be the ubiquitous x86 assemblers from various vendors. Called jump-sizing, most of them are able to perform jump-instruction replacements (long jumps replaced by short or relative jumps) in any number of passes, on request. Others may even do simple rearrangement or insertion of instruct... | https://en.wikipedia.org/wiki/Assembly_language |
instruction set architecture. For instance, an instruction to add memory data to a register in a x86-family processor might be add eax,[ebx], in original Intel syntax, whereas this would be written addl (%ebx),%eax in the AT&T syntax used by the GNU Assembler. Despite different appearances, different syntactic forms g... | https://en.wikipedia.org/wiki/Assembly_language |
eventual definition, telling the linker or the loader to patch the locations where the as yet undefined symbols had been used.
Multi-pass assemblers create a table with all symbols and their values in the first passes, then use the table in later passes to generate code.
In both cases, the assembler must be able to det... | https://en.wikipedia.org/wiki/Assembly_language |
reason for the use of one-pass assemblers was memory size and speed of assembly – often a second pass would require storing the symbol table in memory (to handle forward references), rewinding and rereading the program source on tape, or rereading a deck of cards or punched paper tape. Later computers with much larger ... | https://en.wikipedia.org/wiki/Assembly_language |
mine both addresses in pass 1, so they would be known when generating code in pass 2.
S1 B FWD
...
FWD EQU *
...
BKWD EQU *
...
S2 B BKWD
==== High-level assemblers ====
More sophisticated high-level assemblers provide language abstractions such as:
High-level procedure/function declarations and ... | https://en.wikipedia.org/wiki/Assembly_language |
nstructions and meta-statements (known variously as declarative operations, directives, pseudo-instructions, pseudo-operations and pseudo-ops), comments and data. Assembly language instructions usually consist of an opcode mnemonic followed by an operand, which might be a list of data, arguments or parameters. Some in... | https://en.wikipedia.org/wiki/Assembly_language |
th the data 01100001.
10110000 01100001
This binary computer code can be made more human-readable by expressing it in hexadecimal as follows.
B0 61
Here, B0 means "Move a copy of the following value into AL", and 61 is a hexadecimal representation of the value 01100001, which is 97 in decimal. Assembly language for... | https://en.wikipedia.org/wiki/Assembly_language |
may use separate opcode mnemonics such as L for "move memory to register", ST for "move register to memory", LR for "move register to register", MVI for "move immediate operand to memory", etc.
If the same mnemonic is used for different instructions, that means that the mnemonic corresponds to several different binary ... | https://en.wikipedia.org/wiki/Assembly_language |
e mnemonic can represent more than one binary instruction, the assembler determines which instruction to generate by examining the operands. In the first example, the operand 61h is a valid hexadecimal numeric constant and is not a valid register name, so only the B0 instruction can be applicable. In the second examp... | https://en.wikipedia.org/wiki/Assembly_language |
H, and DH, as well as with any user-defined symbol that ends with the letter H and otherwise contains only characters that are hexadecimal digits, such as the word "BEACH".)
Returning to the original example, while the x86 opcode 10110000 (B0) copies an 8-bit value into the AL register, 10110001 (B1) moves it into CL a... | https://en.wikipedia.org/wiki/Assembly_language |
structions. However, in some cases, an assembler may provide pseudoinstructions (essentially macros) which expand into several machine language instructions to provide commonly needed functionality. For example, for a machine that lacks a "branch if greater or equal" instruction, an assembler may provide a pseudoinstru... | https://en.wikipedia.org/wiki/Assembly_language |
ies. Likewise, since comments in the assembly language source file are ignored by the assembler and have no effect on the object code it generates, a disassembler is always completely unable to recover source comments.
Each computer architecture has its own machine language. Computers differ in the number and type of ... | https://en.wikipedia.org/wiki/Assembly_language |
nemonics are the Intel 8080 family and the Intel 8086/8088. Because Intel claimed copyright on its assembly language mnemonics (on each page of their documentation published in the 1970s and early 1980s, at least), some companies that independently produced CPUs compatible with Intel instruction sets invented their ow... | https://en.wikipedia.org/wiki/Assembly_language |
088 instructions, to avoid accusations of infringement of Intel's copyright. (It is questionable whether such copyrights can be valid, and later CPU companies such as AMD and Cyrix republished Intel's x86/IA-32 instruction mnemonics exactly with neither permission nor legal penalty.) It is doubtful whether in practic... | https://en.wikipedia.org/wiki/Assembly_language |
ements and in the nomenclature that they use. In particular, some describe anything other than a machine mnemonic or extended mnemonic as a pseudo-operation (pseudo-op). A typical assembly language consists of 3 types of instruction statements that are used to define program operations:
Opcode mnemonics
Data definitio... | https://en.wikipedia.org/wiki/Assembly_language |
instruction or implied, or the addresses of data located elsewhere in storage. This is determined by the underlying processor architecture: the assembler merely reflects how this architecture works. Extended mnemonics are often used to specify a combination of an opcode with a specific operand, e.g., the System/360 as... | https://en.wikipedia.org/wiki/Assembly_language |
emblers for System/360 and System/370 use the extended mnemonics NOP and NOPR for BC and BCR with zero masks. For the SPARC architecture, these are known as synthetic instructions.
Some assemblers also support simple built-in macro-instructions that generate two or more machine instructions. For instance, with some Z8... | https://en.wikipedia.org/wiki/Assembly_language |
hich the data section is defined. Some assemblers classify these as pseudo-ops.
==== Assembly directives ====
Assembly directives, also called pseudo-opcodes, pseudo-operations or pseudo-ops, are commands given to an assembler "directing it to perform operations other than assembling instructions". Directives affect ... | https://en.wikipedia.org/wiki/Assembly_language |
sier to read and maintain. Another common use of pseudo-ops is to reserve storage areas for run-time data and optionally initialize their contents to known values.
Symbolic assemblers let programmers associate arbitrary names (labels or symbols) with memory locations and various constants. Usually, every constant and v... | https://en.wikipedia.org/wiki/Assembly_language |
bels that refer to literal values or the result of simple computations performed by the assembler. Labels can also be used to initialize constants and variables with relocatable addresses.
Assembly languages, like most other computer languages, allow comments to be added to program source code that will be ignored duri... | https://en.wikipedia.org/wiki/Assembly_language |
ic machine instructions, and templates for assembler statements. This sequence of text lines may include opcodes or directives. Once a macro has been defined its name may be used in place of a mnemonic. When the assembler processes such a statement, it replaces the statement with the text lines associated with that mac... | https://en.wikipedia.org/wiki/Assembly_language |
y language, the term "macro" represents a more comprehensive concept than it does in some other contexts, such as the pre-processor in the C programming language, where its #define directive typically is used to create short single line macros. Assembler macro instructions, like macros in PL/I and some other languages,... | https://en.wikipedia.org/wiki/Assembly_language |
ating such high-level language elements as optional parameters, symbolic variables, conditionals, string manipulation, and arithmetic operations, all usable during the execution of a given macro, and allowing macros to save context or exchange information. Thus a macro might generate numerous assembly language instruct... | https://en.wikipedia.org/wiki/Assembly_language |
ers are not working with a computer's lowest-level conceptual elements. Underlining this point, macros were used to implement an early virtual machine in SNOBOL4 (1967), which was written in the SNOBOL Implementation Language (SIL), an assembly language for a virtual machine. The target machine would translate this to ... | https://en.wikipedia.org/wiki/Assembly_language |
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