The PERQ referred to as the Three Rivers PERQ or ICL PERQ, was a pioneering workstation computer produced in the late 1970s through the early 1980s. In June 1979, the company took its first order from the UK's Rutherford Appleton Laboratory and the computer was launched in August 1979 at SIGGRAPH in Chicago, it was the first commercially produced personal workstation with a Graphical User Interface. The design was influenced by the original workstation computer, the Xerox Alto, never commercially produced; the origin of the name "PERQ" was chosen both as an acronym of "Pascal Engine that Runs Quicker," and to evoke the word perquisite. The workstation was conceived by six former Carnegie Mellon University alumni and employees, Brian S. Rosen, James R. Teter, William H. Broadley, J. Stanley Kriz, D. Raj Reddy and Paul G. Newbury, who formed the startup Three Rivers Computer Corporation in 1974. Brian Rosen worked at Xerox PARC on the Dolphin workstation; as a result of interest from the UK Science Research Council, 3RCC entered into a relationship with the British computer company ICL in 1981 for European distribution, co-development and manufacturing.
The PERQ was used in a number of academic research projects in the UK during the 1980s. 3RCC was renamed PERQ System Corporation in 1984. It went out of business in 1986 due to competition from other workstation manufacturers such as Sun Microsystems, Apollo Computer and Silicon Graphics; the PERQ CPU was a microcoded discrete logic design, rather than a microprocessor. It was based around an Am2910 microcode sequencer; the PERQ CPU was unusual in having 20-bit wide registers and a writable control store, allowing the microcode to be redefined. The CPU had a microinstruction cycle period of 170 ns; the original PERQ, launched in 1980, was housed in a pedestal-type cabinet with a brown fascia and an 8-inch floppy disk drive mounted horizontally at the top. The PERQ 1 CPU had a WCS comprising 4k words of 48-bit microcode memory; the PERQ 1A CPU extended the WCS to 16k words. The PERQ 1 could be configured with 256 kB, 1MB or 2 MB of 64-bit-wide RAM, a 12 or 24 MB, 14-inch Shugart SA-4000-series hard disk, an 8-inch floppy disk drive.
The internal layout of the PERQ 1 was dominated by the vertically mounted hard disk drive. It was this that determined the height and depth of the chassis; the disk drive was driven by an electric motor, with the two coupled by a rubber-compound belt drive. A basic PERQ 1 system comprised a memory board and an I/O board; the IOB included a Zilog Z80 microprocessor, an IEEE-488 interface, an RS-232 serial port and floppy disk interfaces and speech synthesis hardware. PERQ 1s had a spare Optional I/O board slot for additional interfaces such as Ethernet. A graphics tablet was standard. Most PERQ 1s were supplied with an 8½ ×11-inch, 768×1024 pixel portrait orientation white phosphor monochrome monitor; the PERQ 2 was announced in 1983. The PERQ 2 could be distinguished from the PERQ 1 by its wider, ICL-designed cabinet, with a lighter-coloured fascia, vertical floppy disk drive and three-digit diagnostic display; the PERQ 2 used the same 16k WCS CPU as the PERQ 1A and had a 3-button mouse in place of the graphics tablet.
It was configured with a quieter 8-inch 35 MB Micropolis Corporation 1201 hard disk, 1 or 2 MB of RAM and had the option of the PERQ 1's portrait monitor or a 19-inch, 1280×1024 landscape orientation monitor. Due to manufacturing problems with the original 3RCC PERQ 2, ICL revised the hardware design, resulting in the PERQ 2 T1; the PERQ 2 T2 and PERQ 2 T4 models replaced the 8-inch hard disk with a 5¼-inch hard disk, which allowed for a second disk to be installed internally. The T4 model had backplane bus, allowing the use of a 4 MB RAM board; the PERQ 2 replaced the IOB with either an EIO or NIO boards. These were similar to the IOB, with the addition of a non-volatile real-time clock, a second RS-232 port, an Ethernet interface; the PERQ 3A was developed by ICL as a replacement for the PERQ 2. The PERQ 3A had an all-new hardware architecture based around a 12.5 MHz Motorola 68020 microprocessor and 68881 floating-point unit, plus two AMD 29116A 32-bit bit slice processors which acted as graphics co-processors.
It had up to 2 MB of RAM, a SCSI hard disk and was housed in a desktop "mini-tower"-style enclosure. The operating system was a port of UNIX System V Release 2 called PNX 300. Prototype units were produced in 1985, but the project was cancelled before full production commenced. Another workstation design under development at the time of the company's demise, the PERQ 3B was a colour model was taken over by Crosfield Electronics for its Crosfield Studio 9500 page layout workstation; the workstation was known internally as Python, was developed in 1986 jointly by MegaScan and Conner Scelza Associates and the Crosfield team. MegaScan, led by Brian Rosen, developed the workstation electronics and Conner Scelza Associates ported UNIX and wrote all the ot
An operating system is system software that manages computer hardware and software resources and provides common services for computer programs. Time-sharing operating systems schedule tasks for efficient use of the system and may include accounting software for cost allocation of processor time, mass storage and other resources. For hardware functions such as input and output and memory allocation, the operating system acts as an intermediary between programs and the computer hardware, although the application code is executed directly by the hardware and makes system calls to an OS function or is interrupted by it. Operating systems are found on many devices that contain a computer – from cellular phones and video game consoles to web servers and supercomputers; the dominant desktop operating system is Microsoft Windows with a market share of around 82.74%. MacOS by Apple Inc. is in second place, the varieties of Linux are collectively in third place. In the mobile sector, use in 2017 is up to 70% of Google's Android and according to third quarter 2016 data, Android on smartphones is dominant with 87.5 percent and a growth rate 10.3 percent per year, followed by Apple's iOS with 12.1 percent and a per year decrease in market share of 5.2 percent, while other operating systems amount to just 0.3 percent.
Linux distributions are dominant in supercomputing sectors. Other specialized classes of operating systems, such as embedded and real-time systems, exist for many applications. A single-tasking system can only run one program at a time, while a multi-tasking operating system allows more than one program to be running in concurrency; this is achieved by time-sharing, where the available processor time is divided between multiple processes. These processes are each interrupted in time slices by a task-scheduling subsystem of the operating system. Multi-tasking may be characterized in co-operative types. In preemptive multitasking, the operating system slices the CPU time and dedicates a slot to each of the programs. Unix-like operating systems, such as Solaris and Linux—as well as non-Unix-like, such as AmigaOS—support preemptive multitasking. Cooperative multitasking is achieved by relying on each process to provide time to the other processes in a defined manner. 16-bit versions of Microsoft Windows used cooperative multi-tasking.
32-bit versions of both Windows NT and Win9x, used preemptive multi-tasking. Single-user operating systems have no facilities to distinguish users, but may allow multiple programs to run in tandem. A multi-user operating system extends the basic concept of multi-tasking with facilities that identify processes and resources, such as disk space, belonging to multiple users, the system permits multiple users to interact with the system at the same time. Time-sharing operating systems schedule tasks for efficient use of the system and may include accounting software for cost allocation of processor time, mass storage and other resources to multiple users. A distributed operating system manages a group of distinct computers and makes them appear to be a single computer; the development of networked computers that could be linked and communicate with each other gave rise to distributed computing. Distributed computations are carried out on more than one machine; when computers in a group work in cooperation, they form a distributed system.
In an OS, distributed and cloud computing context, templating refers to creating a single virtual machine image as a guest operating system saving it as a tool for multiple running virtual machines. The technique is used both in virtualization and cloud computing management, is common in large server warehouses. Embedded operating systems are designed to be used in embedded computer systems, they are designed to operate on small machines like PDAs with less autonomy. They are able to operate with a limited number of resources, they are compact and efficient by design. Windows CE and Minix 3 are some examples of embedded operating systems. A real-time operating system is an operating system that guarantees to process events or data by a specific moment in time. A real-time operating system may be single- or multi-tasking, but when multitasking, it uses specialized scheduling algorithms so that a deterministic nature of behavior is achieved. An event-driven system switches between tasks based on their priorities or external events while time-sharing operating systems switch tasks based on clock interrupts.
A library operating system is one in which the services that a typical operating system provides, such as networking, are provided in the form of libraries and composed with the application and configuration code to construct a unikernel: a specialized, single address space, machine image that can be deployed to cloud or embedded environments. Early computers were built to perform a series of single tasks, like a calculator. Basic operating system features were developed in the 1950s, such as resident monitor functions that could automatically run different programs in succession to speed up processing. Operating systems did not exist in their more complex forms until the early 1960s. Hardware features were added, that enabled use of runtime libraries and parallel processing; when personal computers became popular in the 1980s, operating systems were made for them similar in concept to those used on larger computers. In the 1940s, the earliest electronic digital systems had no operating systems.
Electronic systems of this time were programmed on rows of mechanical switches or by jumper wires on plug boards. These were special-purpose systems that, for example, generated ballistics tables for the military or controlled the pri
A computing platform or digital platform is the environment in which a piece of software is executed. It may be the hardware or the operating system a web browser and associated application programming interfaces, or other underlying software, as long as the program code is executed with it. Computing platforms have different abstraction levels, including a computer architecture, an OS, or runtime libraries. A computing platform is the stage. A platform can be seen both as a constraint on the software development process, in that different platforms provide different functionality and restrictions. For example, an OS may be a platform that abstracts the underlying differences in hardware and provides a generic command for saving files or accessing the network. Platforms may include: Hardware alone, in the case of small embedded systems. Embedded systems can access hardware directly, without an OS. A browser in the case of web-based software; the browser itself runs on a hardware+OS platform, but this is not relevant to software running within the browser.
An application, such as a spreadsheet or word processor, which hosts software written in an application-specific scripting language, such as an Excel macro. This can be extended to writing fully-fledged applications with the Microsoft Office suite as a platform. Software frameworks. Cloud computing and Platform as a Service. Extending the idea of a software framework, these allow application developers to build software out of components that are hosted not by the developer, but by the provider, with internet communication linking them together; the social networking sites Twitter and Facebook are considered development platforms. A virtual machine such as the Java virtual machine or. NET CLR. Applications are compiled into a format similar to machine code, known as bytecode, executed by the VM. A virtualized version of a complete system, including virtualized hardware, OS, storage; these allow, for instance, a typical Windows program to run on. Some architectures have multiple layers, with each layer acting as a platform to the one above it.
In general, a component only has to be adapted to the layer beneath it. For instance, a Java program has to be written to use the Java virtual machine and associated libraries as a platform but does not have to be adapted to run for the Windows, Linux or Macintosh OS platforms. However, the JVM, the layer beneath the application, does have to be built separately for each OS. AmigaOS, AmigaOS 4 FreeBSD, NetBSD, OpenBSD IBM i Linux Microsoft Windows OpenVMS Classic Mac OS macOS OS/2 Solaris Tru64 UNIX VM QNX z/OS Android Bada BlackBerry OS Firefox OS iOS Embedded Linux Palm OS Symbian Tizen WebOS LuneOS Windows Mobile Windows Phone Binary Runtime Environment for Wireless Cocoa Cocoa Touch Common Language Infrastructure Mono. NET Framework Silverlight Flash AIR GNU Java platform Java ME Java SE Java EE JavaFX JavaFX Mobile LiveCode Microsoft XNA Mozilla Prism, XUL and XULRunner Open Web Platform Oracle Database Qt SAP NetWeaver Shockwave Smartface Universal Windows Platform Windows Runtime Vexi Ordered from more common types to less common types: Commodity computing platforms Wintel, that is, Intel x86 or compatible personal computer hardware with Windows operating system Macintosh, custom Apple Inc. hardware and Classic Mac OS and macOS operating systems 68k-based PowerPC-based, now migrated to x86 ARM architecture based mobile devices iPhone smartphones and iPad tablet computers devices running iOS from Apple Gumstix or Raspberry Pi full function miniature computers with Linux Newton devices running the Newton OS from Apple x86 with Unix-like systems such as Linux or BSD variants CP/M computers based on the S-100 bus, maybe the earliest microcomputer platform Video game consoles, any variety 3DO Interactive Multiplayer, licensed to manufacturers Apple Pippin, a multimedia player platform for video game console development RISC processor based machines running Unix variants SPARC architecture computers running Solaris or illumos operating systems DEC Alpha cluster running OpenVMS or Tru64 UNIX Midrange computers with their custom operating systems, such as IBM OS/400 Mainframe computers with their custom operating systems, such as IBM z/OS Supercomputer architectures Cross-platform Platform virtualization Third platform Ryan Sarver: What is a platform
A workstation is a special computer designed for technical or scientific applications. Intended to be used by one person at a time, they are connected to a local area network and run multi-user operating systems; the term workstation has been used loosely to refer to everything from a mainframe computer terminal to a PC connected to a network, but the most common form refers to the group of hardware offered by several current and defunct companies such as Sun Microsystems, Silicon Graphics, Apollo Computer, DEC, HP, NeXT and IBM which opened the door for the 3D graphics animation revolution of the late 1990s. Workstations offered higher performance than mainstream personal computers with respect to CPU and graphics, memory capacity, multitasking capability. Workstations were optimized for the visualization and manipulation of different types of complex data such as 3D mechanical design, engineering simulation and rendering of images, mathematical plots; the form factor is that of a desktop computer, consist of a high resolution display, a keyboard and a mouse at a minimum, but offer multiple displays, graphics tablets, 3D mice, etc.
Workstations were the first segment of the computer market to present advanced accessories and collaboration tools. The increasing capabilities of mainstream PCs in the late 1990s have blurred the lines somewhat with technical/scientific workstations; the workstation market employed proprietary hardware which made them distinct from PCs. However, by the early 2000s this difference disappeared, as workstations now use commoditized hardware dominated by large PC vendors, such as Dell, Hewlett-Packard and Fujitsu, selling Microsoft Windows or Linux systems running on x86-64 processors; the first computer that might qualify as a "workstation" was the IBM 1620, a small scientific computer designed to be used interactively by a single person sitting at the console. It was introduced in 1960. One peculiar feature of the machine was. To perform addition, it required a memory-resident table of decimal addition rules; this saved on the cost of logic circuitry. The machine was code-named CADET and rented for $1000 a month.
In 1965, IBM introduced the IBM 1130 scientific computer, meant as the successor to the 1620. Both of these systems came with the ability to run programs written in other languages. Both the 1620 and the 1130 were built into desk-sized cabinets. Both were available with add-on disk drives and both paper-tape and punched-card I/O. A console typewriter for direct interaction was standard on each. Early examples of workstations were dedicated minicomputers. A notable example was the PDP-8 from Digital Equipment Corporation, regarded to be the first commercial minicomputer; the Lisp machines developed at MIT in the early 1970s pioneered some of the principles of the workstation computer, as they were high-performance, single-user systems intended for interactive use. Lisp Machines were commercialized beginning 1980 by companies like Symbolics, Lisp Machines, Texas Instruments and Xerox; the first computer designed for single-users, with high-resolution graphics facilities was the Xerox Alto developed at Xerox PARC in 1973.
Other early workstations include the Terak 8510/a, Three Rivers PERQ and the Xerox Star. In the early 1980s, with the advent of 32-bit microprocessors such as the Motorola 68000, a number of new participants in this field appeared, including Apollo Computer and Sun Microsystems, who created Unix-based workstations based on this processor. Meanwhile, DARPA's VLSI Project created several spinoff graphics products as well, notably the SGI 3130, Silicon Graphics' range of machines that followed, it was not uncommon to differentiate the target market for the products, with Sun and Apollo considered to be network workstations, while the SGI machines were graphics workstations. As RISC microprocessors became available in the mid-1980s, these were adopted by many workstation vendors. Workstations tended to be expensive several times the cost of a standard PC and sometimes costing as much as a new car. However, minicomputers sometimes cost as much as a house; the high expense came from using costlier components that ran faster than those found at the local computer store, as well as the inclusion of features not found in PCs of the time, such as high-speed networking and sophisticated graphics.
Workstation manufacturers tend to take a "balanced" approach to system design, making certain to avoid bottlenecks so that data can flow unimpeded between the many different subsystems within a computer. Additionally, given their more specialized nature, tend to have higher profit margins than commodity-driven PCs; the systems that come out of workstation companies feature SCSI or Fibre Channel disk storage systems, high-end 3D accelerators, single or multiple 64-bit processors, large amounts of RAM, well-designed cooling. Additionally, the companies that make the products tend to have good repair/replacement plans. However, the line between workstation and PC is becoming blurred as the demand for fast computers and graphics have become
Digital Equipment Corporation's PDP-10 marketed as the DECsystem-10, was a mainframe computer family manufactured beginning in 1966. 1970s models and beyond were marketed under the DECsystem-10 name as the TOPS-10 operating system became used. The PDP-10's architecture is identical to that of DEC's earlier PDP-6, sharing the same 36-bit word length and extending the instruction set; some aspects of the instruction set are unusual, most notably the byte instructions, which operated on bit fields of any size from 1 to 36 bits inclusive, according to the general definition of a byte as a contiguous sequence of a fixed number of bits. The PDP-10 is the machine that made time-sharing common, this and other features made it a common fixture in many university computing facilities and research labs during the 1970s, the most notable being Harvard University's Aiken Lab, MIT's AI Lab and Project MAC, Stanford's SAIL, Computer Center Corporation, ETH, Carnegie Mellon University, its main operating systems, TOPS-10 and TENEX, were used to build out the early ARPANET.
For these reasons, the PDP-10 looms large in early hacker folklore. Projects to extend the PDP-10 line were eclipsed by the success of the unrelated VAX superminicomputer, the cancellation of the PDP-10 line was announced in 1983; the original PDP-10 processor is the KA10, introduced in 1968. It uses discrete transistors packaged in DEC's Flip-Chip technology, with backplanes wire wrapped via a semi-automated manufacturing process, its cycle time is its add time 2.1 μs. In 1973, the KA10 was replaced by the KI10, which uses transistor–transistor logic SSI; this was joined in 1975 by the higher-performance KL10, built from emitter-coupled logic and has cache memory. The KL10's performance was about 1 megaflops using 36-bit floating point numbers on matrix row reduction, it was faster than the newer VAX-11/750, although more limited in memory. A smaller, less expensive model, the KS10, was introduced in 1978, using TTL and Am2901 bit-slice components and including the PDP-11 Unibus to connect peripherals.
The KS was marketed as the DECsystem-2020, DEC's entry in the distributed processing arena, it was introduced as "the world's lowest cost mainframe computer system." The KA10 has a maximum main memory capacity of 256 kilowords. As supplied by DEC, it did not include paging hardware; this allows each half of a user's address space to be limited to a set section of main memory, designated by the base physical address and size. This allows the model of separate read-only shareable code segment and read-write data/stack segment used by TOPS-10 and adopted by Unix; some KA10 machines, first at MIT, at Bolt and Newman, were modified to add virtual memory and support for demand paging, more physical memory. KA10 weighed about 1,920 pounds; the 10/50 was the top-of-the-line Uni-processor KA machine at the time when the PA1050 software package was introduced. Two other KA10 models were the uniprocessor 10/40, the dual-processor 10/55; the KI10 and processors offer paged memory management, support a larger physical address space of 4 megawords.
KI10 models include 1060, 1070 and 1077, the latter incorporating two CPUs. The original KL10 PDP-10 models use the original PDP-10 memory bus, with external memory modules. Module in this context meant a cabinet, dimensions 30 x 75 x 30 in. with a capacity of 32 to 256 kWords of magnetic core memory. The processors used in the DECSYSTEM-20 but incorrectly called "KL20", use internal memory, mounted in the same cabinet as the CPU; the 10xx models have different packaging. The differences between the 10xx and 20xx models are more cosmetic than real. In particular, all ARPAnet TOPS-20 systems had an I/O bus because the AN20 IMP interface was an I/O bus device. Both could run thus the corresponding operating system; the "Model B" version of the 2060 processors removed the 256 kiloword limit on the virtual address space, by allowing the use of up to 32 "sections" of up to 256 kilowords each, along with substantial changes to the instruction set. "Model A" and "Model B" KL10. The first operating system that took advantage of the Model B's capabilities was TOPS-20 release 3, user mode extended addressing was offered in TOPS-20 release 4.
TOPS-20 versions after release 4.1 would only run on a Model B. TOPS-10 versions 7.02 and 7.03 use extended addressing when run on a 1090 Model B processor running TOPS-20 microcode. The final upgrade to the KL10 was the MCA25 upgrade of a 2060 to 2065, which gave some performance increases for programs which run in multiple sections; the KS10 design was crippled to be a Model A though most of the necessary data paths needed to support the Model B architecture were present. This was no doubt intended to segment the market, but it shortened the KS10's product life. Frontend processors are comp
Carnegie Mellon University
Carnegie Mellon University is a private research university based in Pittsburgh, Pennsylvania. Founded in 1900 by Andrew Carnegie as the Carnegie Technical Schools, the university became the Carnegie Institute of Technology in 1912 and began granting four-year degrees. In 1967, the Carnegie Institute of Technology merged with the Mellon Institute of Industrial Research to form Carnegie Mellon University. With its main campus located 3 miles from Downtown Pittsburgh, Carnegie Mellon has grown into an international university with over a dozen degree-granting locations in six continents, including campuses in Qatar and Silicon Valley, more than 20 research partnerships; the university has seven colleges and independent schools which all offer interdisciplinary programs: the College of Engineering, College of Fine Arts, Dietrich College of Humanities and Social Sciences, Mellon College of Science, Tepper School of Business, H. John Heinz III College of Information Systems and Public Policy, the School of Computer Science.
Carnegie Mellon counts 13,961 students from 109 countries, over 105,000 living alumni, over 5,000 faculty and staff. Past and present faculty and alumni include 20 Nobel Prize laureates, 13 Turing Award winners, 23 Members of the American Academy of Arts and Sciences, 22 Fellows of the American Association for the Advancement of Science, 79 Members of the National Academies, 124 Emmy Award winners, 47 Tony Award laureates, 10 Academy Award winners; the Carnegie Technical Schools were founded in 1900 in Pittsburgh by the Scottish American industrialist and philanthropist Andrew Carnegie, who wrote the time-honored words "My heart is in the work", when he donated the funds to create the institution. Carnegie's vision was to open a vocational training school for the sons and daughters of working-class Pittsburghers. Carnegie was inspired for the design of his school by the Pratt Institute in Brooklyn, New York founded by industrialist Charles Pratt in 1887. In 1912, the institution changed its name to Carnegie Institute of Technology and began offering four-year degrees.
During this time, CIT consisted of four constituent schools: the School of Fine and Applied Arts, the School of Apprentices and Journeymen, the School of Science and Technology, the Margaret Morrison Carnegie School for Women. The Mellon Institute of Industrial Research was founded in 1913 by a banker and industrialist brothers Andrew and Richard B. Mellon in honor of their father, Thomas Mellon, the patriarch of the Mellon family; the Institute began as a research organization which performed work for government and industry on a contract and was established as a department within the University of Pittsburgh. In 1927, the Mellon Institute incorporated as an independent nonprofit. In 1938, the Mellon Institute's iconic building was completed and it moved to its new, current, location on Fifth Avenue. In 1967, with support from Paul Mellon, Carnegie Tech merged with the Mellon Institute of Industrial Research to become Carnegie Mellon University. Carnegie Mellon's coordinate women's college, the Margaret Morrison Carnegie College closed in 1973 and merged its academic programs with the rest of the university.
The industrial research mission of the Mellon Institute survived the merger as the Carnegie Mellon Research Institute and continued doing work on contract to industry and government. CMRI closed in 2001 and its programs were subsumed by other parts of the university or spun off into autonomous entities. Carnegie Mellon's 140-acre main campus is three miles from downtown Pittsburgh, between Schenley Park and the Squirrel Hill and Oakland neighborhoods. Carnegie Mellon is bordered to the west by the campus of the University of Pittsburgh. Carnegie Mellon owns 81 buildings in the Squirrel Hill neighborhoods of Pittsburgh. For decades the center of student life on campus was the University's student union. Built in the 1950s, Skibo Hall's design was typical of Mid-Century Modern architecture, but was poorly equipped to deal with advances in computer and internet connectivity; the original Skibo was razed in the summer of 1994 and replaced by a new student union, wi-fi enabled. Known as University Center, the building was dedicated in 1996.
In 2014, Carnegie Mellon re-dedicated the University Center as the Cohon University Center in recognition of the eighth president of the university, Jared Cohon. A large grassy area known as "the Cut" forms the backbone of the campus, with a separate grassy area known as "the Mall" running perpendicular; the Cut was formed by filling in a ravine with soil from a nearby hill, leveled to build the College of Fine Arts building. The northwestern part of the campus was acquired from the United States Bureau of Mines in the 1980s. In 2006, Carnegie Mellon Trustee Jill Gansman Kraus donated the 80-foot -tall sculpture Walking to the Sky, placed on the lawn facing Forbes Ave between the Cohon University Center and Warner Hall; the sculpture was controversial for its placement, the general lack of input that the campus community had, its aesthetic appeal. In April 2015, Carnegie Mellon University, in collaboration with Jones Lang LaSalle, announced the planning of a second office space structure, alongside the Robert Mehrabian Collaborative Innovation Center, an upscale and full-service hotel, retail and dining development along Forbes Avenue.
This complex will connect to the Tepper Quadrangle, the Heinz College, the Tata Consultancy Services Building, the Gates-Hillman Center to create an innovation corridor on the university campus. The eff
In computer science, computer engineering and programming language implementations, a stack machine is a type of computer. In some cases, the term refers to a software scheme; the main difference from other computers is that most of its instructions operate on a pushdown stack of numbers rather than numbers in registers. Most computer systems link to subroutines; this does not make these computers stack machines. The common alternative to a stack machine is a register machine, in which each instruction explicitly names specific registers for its operands and result. A "stack machine" is a computer that uses a last-in, first-out stack to hold short-lived temporary values. Most of its instructions assume that operands will be from the stack, results placed in the stack. For a typical instruction such as Add the computer takes both operands from the topmost values of the stack; the computer replaces those two values with the sum, which the computer calculates when it performs the Add instruction. The instruction's operands are "popped" off the stack, its result are "pushed" back onto the stack, ready for the next instruction.
Most stack instructions have only an opcode commanding an operation, with no additional fields to identify a constant, register or memory cell. The stack holds more than two inputs or more than one result, so a richer set of operations can be computed. Integer constant operands are pushed by separate Load Immediate instructions. Memory is accessed by separate Load or Store instructions containing a memory address or calculating the address from values in the stack. For speed, a stack machine implements some part of its stack with registers. To execute operands of the arithmetic logic unit may be the top two registers of the stack and the result from the ALU is stored in the top register of the stack; some stack machines have a stack of limited size, implemented as a register file. The ALU will access this with an index; some machines have a stack of unlimited size, implemented as an array in RAM accessed by a "top of stack" address register. This is slower, but the number of flip-flops is less, making a less-expensive, more compact CPU.
Its topmost N values may be cached for speed. A few machines have both an expression stack in a separate register stack. In this case, software, or an interrupt may move data between them; the instruction set carries out most ALU actions with postfix operations that work only on the expression stack, not on data registers or main memory cells. This can be convenient for executing high-level languages, because most arithmetic expressions can be translated into postfix notation. In contrast, register machines hold temporary values in a fast array of registers. Accumulator machines have only one general-purpose register. Belt machines use a FIFO queue to hold temporary values. Memory-to-memory machines do not have any temporary registers usable by a programmer. Stack machines may have their expression stack and their call-return stack separated or as one integrated structure. If they are separated, the instructions of the stack machine can be pipelined with fewer interactions and less design complexity.
It can run faster. Some technical handheld calculators use reverse Polish notation in their keyboard interface, instead of having parenthesis keys; this is a form of stack machine. The Plus key relies on its two operands being at the correct topmost positions of the user-visible stack. Stack machines have much smaller instructions than the other styles of machines. Loads and stores to memory are separate and so stack code requires twice as many instructions as the equivalent code for register machines; the total code size is still less for stack machines. In stack machine code, the most frequent instructions consist of just an opcode selecting the operation; this can fit in 6 bits or less. Branches, load immediates, load/store instructions require an argument field, but stack machines arrange that the frequent cases of these still fit together with the opcode into a compact group of bits; the selection of operands from prior results is done implicitly by ordering the instructions. In contrast, register machines require two or three register-number fields per ALU instruction to select operands.
The instructions for accumulator or memory-to-memory machines are not padded out with multiple register fields. Instead, they use compiler-managed anonymous variables for subexpression values; these temporary locations require extra memory reference instructions which take more code space than for the stack machine, or compact register machines. All practical stack machines have variants of the load–store opcodes for accessing local variables and formal parameters without explicit address calculations; this can be by offsets from the current top-of-stack address, or by offsets from a stable frame-base register. Register machines handle this with a register + use a wider offset field. Dense machine code was valuable in the 1960s, when main memory was expensive and limited on mainframes, it became important again on the initially-tiny memories of minicomputers and microprocessors. Density remains important today, for smartphone applications, applications downloaded into browsers over slow Internet connections, in ROMs for embedded applications.
A more general advantage of increased density is improved effectiveness of caches and instruction prefetch. Some of the density of Burroughs B6700 code was due to moving vital operand information elsewhere