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5,901 | Some control units do branch prediction: A control unit keeps an electronic list of the recent branches, encoded by the address of the branch instruction. This list has a few bits for each branch to remember the direction that was taken most recently. |
5,902 | Some control units can do speculative execution, in which a computer might have two or more pipelines, calculate both directions of a branch, and then discard the calculations of the unused direction. |
5,903 | Results from memory can become available at unpredictable times because very fast computers cache memory. That is, they copy limited amounts of memory data into very fast memory. The CPU must be designed to process at the very fast speed of the cache memory. Therefore, the CPU might stall when it must access main memor... |
5,904 | To help this, out-of-order CPUs and control units were developed to process data as it becomes available. |
5,905 | But what if all the calculations are complete, but the CPU is still stalled, waiting for main memory? Then, a control unit can switch to an alternative thread of execution whose data has been fetched while the thread was idle. A thread has its own program counter, a stream of instructions and a separate set of register... |
5,906 | When a control unit permits threads, the software also has to be designed to handle them. In general-purpose CPUs like PCs and smartphones, the threads are usually made to look very like normal time-sliced processes. At most, the operating system might need some awareness of them. In GPUs, the thread scheduling usually... |
5,907 | A control unit can be designed to finish what it can. If several instructions can be completed at the same time, the control unit will arrange it. So, the fastest computers can process instructions in a sequence that can vary somewhat, depending on when the operands or instruction destinations become available. Most su... |
5,908 | When the execution of calculations is the slowest, instructions flow from memory into pieces of electronics called "issue units." An issue unit holds an instruction until both its operands and an execution unit are available. Then, the instruction and its operands are "issued" to an execution unit. The execution unit d... |
5,909 | It is common to have specialized execution units. For example, a modestly priced computer might have only one floating-point execution unit, because floating point units are expensive. The same computer might have several integer units, because these are relatively inexpensive, and can do the bulk of instructions. |
5,910 | One kind of control unit for issuing uses an array of electronic logic, a "scoreboard"" that detects when an instruction can be issued. The "height" of the array is the number of execution units, and the "length" and "width" are each the number of sources of operands. When all the items come together, the signals from ... |
5,911 | With some additional logic, a scoreboard can compactly combine execution reordering, register renaming and precise exceptions and interrupts. Further it can do this without the power-hungry, complex content-addressable memory used by the Tomasulo algorithm. |
5,912 | If the execution is slower than writing the results, the memory write-back queue always has free entries. But what if the memory writes slowly? Or what if the destination register will be used by an "earlier" instruction that has not yet issued? Then the write-back step of the instruction might need to be scheduled. Th... |
5,913 | Retiring logic can also be designed into an issuing scoreboard or a Tomasulo queue, by including memory or register access in the issuing logic. |
5,914 | Out of order controllers require special design features to handle interrupts. When there are several instructions in progress, it is not clear where in the instruction stream an interrupt occurs. For input and output interrupts, almost any solution works. However, when a computer has virtual memory, an interrupt occur... |
5,915 | Also, out of order CPUs have even more problems with stalls from branching, because they can complete several instructions per clock cycle, and usually have many instructions in various stages of progress. So, these control units might use all of the solutions used by pipelined processors. |
5,916 | Some computers translate each single instruction into a sequence of simpler instructions. The advantage is that an out of order computer can be simpler in the bulk of its logic, while handling complex multi-step instructions. x86 Intel CPUs since the Pentium Pro translate complex CISC x86 instructions to more RISC-like... |
5,917 | In these, the "front" of the control unit manages the translation of instructions. Operands are not translated. The "back" of the CU is an out-of-order CPU that issues the micro-operations and operands to the execution units and data paths. |
5,918 | Many modern computers have controls that minimize power usage. In battery-powered computers, such as those in cell-phones, the advantage is longer battery life. In computers with utility power, the justification is to reduce the cost of power, cooling or noise. |
5,919 | Most modern computers use CMOS logic. CMOS wastes power in two common ways: By changing state, i.e. "active power," and by unintended leakage. The active power of a computer can be reduced by turning off control signals. Leakage current can be reduced by reducing the electrical pressure, the voltage, making the transi... |
5,920 | Active power is easier to reduce because data stored in the logic is not affected. The usual method reduces the CPU's clock rate. Most computer systems use this method. It is common for a CPU to idle during the transition to avoid side-effects from the changing clock. |
5,921 | Most computers also have a "halt" instruction. This was invented to stop non-interrupt code so that interrupt code has reliable timing. However, designers soon noticed that a halt instruction was also a good time to turn off a CPU's clock completely, reducing the CPU's active power to zero. The interrupt controller mig... |
5,922 | These methods are relatively easy to design, and became so common that others were invented for commercial advantage. Many modern low-power CMOS CPUs stop and start specialized execution units and bus interfaces depending on the needed instruction. Some computers even arrange the CPU's microarchitecture to use transfer... |
5,923 | One common method is to spread the load to many CPUs, and turn off unused CPUs as the load reduces. The operating system's task switching logic saves the CPUs' data to memory. In some cases, one of the CPUs can be simpler and smaller, literally with fewer logic gates. So, it has low leakage, and it is the last to be tu... |
5,924 | Theoretically, computers at lower clock speeds could also reduce leakage by reducing the voltage of the power supply. This affects the reliability of the computer in many ways, so the engineering is expensive, and it is uncommon except in relatively expensive computers such as PCs or cellphones. |
5,925 | Some designs can use very low leakage transistors, but these usually add cost. The depletion barriers of the transistors can be made larger to have less leakage, but this makes the transistor larger and thus both slower and more expensive. Some vendors use this technique in selected portions of an IC by constructing lo... |
5,926 | Managing leakage is more difficult, because before the logic can be turned-off, the data in it must be moved to some type of low-leakage storage. |
5,927 | Some CPUs make use of a special type of flip-flop that couples a fast, high-leakage storage cell to a slow, large low-leakage cell. These two cells have separated power supplies. When the CPU enters a power saving mode , data is transferred to the low-leakage cells, and the others are turned off. When the CPU leaves... |
5,928 | Older designs would copy the CPU state to memory, or even disk, sometimes with specialized software. Very simple embedded systems sometimes just restart. |
5,929 | All modern CPUs have control logic to attach the CPU to the rest of the computer. In modern computers, this is usually a bus controller. When an instruction reads or writes memory, the control unit either controls the bus directly, or controls a bus controller. Many modern computers use the same bus interface for memor... |
5,930 | A modern CPU also tends to include an interrupt controller. It handles interrupt signals from the system bus. The control unit is the part of the computer that responds to the interrupts. |
5,931 | There is often a cache controller to cache memory. The cache controller and the associated cache memory is often the largest physical part of a modern, higher-performance CPU. When the memory, bus or cache is shared with other CPUs, the control logic must communicate with them to assure that no computer ever gets out-o... |
5,932 | Many historic computers built some type of input and output directly into the control unit. For example, many historic computers had a front panel with switches and lights directly controlled by the control unit. These let a programmer directly enter a program and debug it. In later production computers, the most commo... |
5,933 | Most PDP-8 models had a data bus designed to let I/O devices borrow the control unit's memory read and write logic. This reduced the complexity and expense of high speed I/O controllers, e.g. for disk. |
5,934 | The Xerox Alto had a multitasking microprogrammable control unit that performed almost all I/O. This design provided most of the features of a modern PC with only a tiny fraction of the electronic logic. The dual-thread computer was run by the two lowest-priority microthreads. These performed calculations whenever I/O ... |
5,935 | Thus a program of instructions in memory will cause the CU to configure a CPU's data flows to manipulate the data correctly between instructions. This results in a computer that could run a complete program and require no human intervention to make hardware changes between instructions . |
5,936 | Hardwired control units are implemented through use of combinational logic units, featuring a finite number of gates that can generate specific results based on the instructions that were used to invoke those responses. Hardwired control units are generally faster than the microprogrammed designs. |
5,937 | This design uses a fixed architecture—it requires changes in the wiring if the instruction set is modified or changed. It can be convenient for simple, fast computers. |
5,938 | A controller that uses this approach can operate at high speed; however, it has little flexibility. A complex instruction set can overwhelm a designer who uses ad hoc logic design. |
5,939 | The hardwired approach has become less popular as computers have evolved. Previously, control units for CPUs used ad hoc logic, and they were difficult to design. |
5,940 | The idea of microprogramming was introduced by Maurice Wilkes in 1951 as an intermediate level to execute computer program instructions. Microprograms were organized as a sequence of microinstructions and stored in special control memory. The algorithm for the microprogram control unit, unlike the hardwired control uni... |
5,941 | A popular variation on microcode is to debug the microcode using a software simulator. Then, the microcode is a table of bits. This is a logical truth table, that translates a microcode address into the control unit outputs. This truth table can be fed to a computer program that produces optimized electronic logic. Th... |
5,942 | A resistive network is a network containing only resistors and ideal current and voltage sources. Analysis of resistive networks is less complicated than analysis of networks containing capacitors and inductors. If the sources are constant sources, the result is a DC network. The effective resistance and current distr... |
5,943 | A network that contains active electronic components is known as an electronic circuit. Such networks are generally nonlinear and require more complex design and analysis tools. |
5,944 | An active network contains at least one voltage source or current source that can supply energy to the network indefinitely. A passive network does not contain an active source. |
5,945 | An active network contains one or more sources of electromotive force. Practical examples of such sources include a battery or a generator. Active elements can inject power to the circuit, provide power gain, and control the current flow within the circuit. |
5,946 | Passive networks do not contain any sources of electromotive force. They consist of passive elements like resistors and capacitors. |
5,947 | A network is linear if its signals obey the principle of superposition; otherwise it is non-linear. Passive networks are generally taken to be linear, but there are exceptions. For instance, an inductor with an iron core can be driven into saturation if driven with a large enough current. In this region, the behavio... |
5,948 | Discrete passive components are called lumped elements because all of their, respectively, resistance, capacitance and inductance is assumed to be located at one place. This design philosophy is called the lumped-element model and networks so designed are called lumped-element circuits. This is the conventional app... |
5,949 | A distributed-element circuit that includes some lumped components is called a semi-lumped design. An example of a semi-lumped circuit is the combline filter. |
5,950 | Sources can be classified as independent sources and dependent sources. |
5,951 | An ideal independent source maintains the same voltage or current regardless of the other elements present in the circuit. Its value is either constant or sinusoidal . The strength of voltage or current is not changed by any variation in the connected network. |
5,952 | Dependent sources depend upon a particular element of the circuit for delivering the power or voltage or current depending upon the type of source it is. |
5,953 | A number of electrical laws apply to all linear resistive networks. These include: |
5,954 | Applying these laws results in a set of simultaneous equations that can be solved either algebraically or numerically. The laws can generally be extended to networks containing reactances. They cannot be used in networks that contain nonlinear or time-varying components. |
5,955 | To design any electrical circuit, either analog or digital, electrical engineers need to be able to predict the voltages and currents at all places within the circuit. Simple linear circuits can be analyzed by hand using complex number theory. In more complex cases the circuit may be analyzed with specialized computer... |
5,956 | Circuit simulation software, such as HSPICE , and languages such as VHDL-AMS and verilog-AMS allow engineers to design circuits without the time, cost and risk of error involved in building circuit prototypes. |
5,957 | More complex circuits can be analyzed numerically with software such as SPICE or GNUCAP, or symbolically using software such as SapWin. |
5,958 | When faced with a new circuit, the software first tries to find a steady state solution, that is, one where all nodes conform to Kirchhoff's current law and the voltages across and through each element of the circuit conform to the voltage/current equations governing that element. |
5,959 | Once the steady state solution is found, the operating points of each element in the circuit are known. For a small signal analysis, every non-linear element can be linearized around its operation point to obtain the small-signal estimate of the voltages and currents. This is an application of Ohm's Law. The resulti... |
5,960 | Software such as the PLECS interface to Simulink uses piecewise-linear approximation of the equations governing the elements of a circuit. The circuit is treated as a completely linear network of ideal diodes. Every time a diode switches from on to off or vice versa, the configuration of the linear network changes. ... |
5,961 | Computer hardware includes the physical parts of a computer, such as the central processing unit , random access memory , motherboard, computer data storage, graphics card, sound card, and computer case. It includes external devices such as a monitor, mouse, keyboard, and speakers. |
5,962 | By contrast, software is the set of instructions that can be stored and run by hardware. Hardware is so-termed because it is hard or rigid with respect to changes, whereas software is soft because it is easy to change. |
5,963 | Hardware is typically directed by the software to execute any command or instruction. A combination of hardware and software forms a usable computing system, although other systems exist with only hardware. |
5,964 | The template for all modern computers is the Von Neumann architecture, detailed in a 1945 paper by Hungarian mathematician John von Neumann. The paper describes a design architecture for an electronic digital computer with subdivisions of a processing unit consisting of an arithmetic logic unit and processor registers,... |
5,965 | The personal computer is one of the most common types of computer due to its versatility and relatively low price. Desktop personal computers have a monitor, a keyboard, a mouse, and a computer case. The computer case holds the motherboard, fixed or removable disk drives for data storage, the power supply, and may con... |
5,966 | Laptops are designed for portability but operate similarly to desktop PCs. They may use lower-power or reduced size components, with lower performance than a similarly priced desktop computer. Laptops contain the keyboard, display, and processor in one case. The monitor in the folding upper cover of the case can be clo... |
5,967 | Tablets are portable computers that use a touch screen as the primary input device. Tablets generally weigh less and are smaller than laptops. |
5,968 | Some tablets include fold-out keyboards or offer connections to separate external keyboards. Some models of laptop computers have a detachable keyboard, which allows the system to be configured as a touch-screen tablet. They are sometimes called "2-in-1 detachable laptops" or "tablet-laptop hybrids". |
5,969 | A computer case encloses most of the components of a desktop computer system. It provides mechanical support and protection for internal elements such as the motherboard, disk drives, and power supply, and controls and directs the flow of cooling air over internal components. The case is also part of the system to cont... |
5,970 | A power supply unit converts alternating current electric power to low-voltage direct current power for the computer. The PSU typically uses a switched-mode power supply , with power MOSFETs used in the converters and regulator circuits of the SMPS. |
5,971 | Laptops can run on a built-in rechargeable battery.
Laptops can run on a built-in rechargeable battery. |
5,972 | The motherboard is the main component of a computer. It is a board with integrated circuitry that connects the other parts of the computer including the CPU, the RAM, the disk drives as well as any peripherals connected via the ports or the expansion slots. The integrated circuit chips in a computer typically contain... |
5,973 | Components directly attached to or to part of the motherboard include: |
5,974 | An expansion card in computing is a printed circuit board that can be inserted into an expansion slot of a computer motherboard or backplane to add functionality to a computer system via the expansion bus. Expansion cards can be used to obtain or expand on features not offered by the motherboard. |
5,975 | A storage device is computer hardware or digital media that is used for storing, porting, and extracting data files and objects. It can hold and store information either temporarily or permanently and can be internal or external to a computer. Data storage is a core function and fundamental component of computers. Dedi... |
5,976 | Data is stored by a computer using a variety of media. Hard disk drives are found in virtually all older computers, due to their high capacity and low cost, but solid-state drives are faster and more power efficient, although currently more expensive than hard drives in terms of dollar per gigabyte, so are often foun... |
5,977 | To transfer data between computers, an external flash memory device or optical disc may be used. Their usefulness depends on being readable by other systems; the majority of machines have an optical disk drive , and virtually all have at least one Universal Serial Bus port. USB sticks are typically pre-formatted wit... |
5,978 | Input and output devices are typically housed externally to the main computer chassis. The following are either standard or very common to many computer systems. |
5,979 | Input devices allow the user to enter information into the system, or control its operation. Most personal computers have a mouse and keyboard, but laptop systems typically use a touchpad instead of a mouse. Other input devices include webcams, microphones, joysticks, and image scanners. |
5,980 | Output devices are designed around the senses of human beings. For example, monitors display text that can be read, speakers produce sound that can be heard. Such devices also could include printers or a Braille embosser. |
5,981 | A mainframe computer is a much larger computer that typically fills a room and may cost many hundreds or thousands of times as much as a personal computer. They are designed to perform large numbers of calculations for governments and large enterprises. |
5,982 | In the 1960s and 1970s, more and more departments started to use cheaper and dedicated systems for specific purposes like process control and laboratory automation. A minicomputer, or colloquially mini, is a class of smaller computers that was developed in the mid-1960s and sold for much less than mainframe and mid-siz... |
5,983 | A supercomputer is superficially similar to a mainframe but is instead intended for extremely demanding computational tasks. As of November 2021, the fastest supercomputer on the TOP500 supercomputer list is Fugaku, in Japan, with a LINPACK benchmark score of 415 PFLOPS, superseding the second fastest, Summit, in the U... |
5,984 | The term supercomputer does not refer to a specific technology. Rather it indicates the fastest computations available at any given time. In mid-2011, the fastest supercomputers boasted speeds exceeding one petaflop, or 1 quadrillion floating-point operations per second.
Supercomputers are fast but extremely costly, s... |
5,985 | When using computer hardware, an upgrade means adding new or additional hardware to a computer that improves its performance, increases its capacity, or adds new features. For example, a user could perform a hardware upgrade to replace the hard drive with a faster one or a solid state drive to get a boost in performan... |
5,986 | In large organizations, hardware upgrades are handled by administrators who are also in charge of keeping networks running smoothly. They replace network devices like servers, routers and storage devices based on new demands and capacities. |
5,987 | Global revenue from computer hardware in 2023 reached $705.17 billion. |
5,988 | Because computer parts contain hazardous materials, there is a growing movement to recycle old and outdated parts. Computer hardware contain dangerous chemicals such as lead, mercury, nickel, and cadmium. According to the EPA these e-wastes have a harmful effect on the environment unless they are disposed of properly. ... |
5,989 | Many materials used in computer hardware can be recovered by recycling for use in future production. Reuse of tin, silicon, iron, aluminum, and a variety of plastics that are present in bulk in computers or other electronics can reduce the costs of constructing new systems. Components frequently contain copper, gold, t... |
5,990 | The central processing unit contains many toxic materials. It contains lead and chromium in the metal plates. Resistors, semiconductors, infrared detectors, stabilizers, cables, and wires contain cadmium. The circuit boards in a computer contain mercury, and chromium. When these types of materials, and chemicals are di... |
5,991 | According to the United States Environmental Protection Agency only around 15% of the e-waste actually is recycled. When e-waste byproducts leach into groundwater, are burned, or get mishandled during recycling, it causes harm. Health problems associated with such toxins include impaired mental development, cancer, and... |
5,992 | Computer components contain many toxic substances, like dioxins, polychlorinated biphenyls , cadmium, chromium, radioactive isotopes and mercury. Circuit boards contain considerable quantities of lead-tin solders that are more likely to leach into groundwater or create air pollution due to incineration. In US landfills... |
5,993 | Recycling of computer hardware is considered environmentally friendly because it prevents hazardous waste, including heavy metals and carcinogens, from entering the atmosphere, landfill or waterways. While electronics consist a small fraction of total waste generated, they are far more dangerous. There is stringent leg... |
5,994 | As computer hardware contain a wide number of metals inside, the United States Environmental Protection Agency encourages the collection and recycling of computer hardware. "E-cycling", the recycling of computer hardware, refers to the donation, reuse, shredding and general collection of used electronics. Generically,... |
5,995 | Some companies, such as Dell and Apple, will recycle computers of their make or any other make. Otherwise, a computer can be donated to Computer Aid International which is an organization that recycles and refurbishes old computers for hospitals, schools, universities, etc. |
5,996 | In modern terminology, a microcontroller is similar to, but less sophisticated than, a system on a chip . A SoC may include a microcontroller as one of its components, but usually integrates it with advanced peripherals like a graphics processing unit , a Wi-Fi module, or one or more coprocessors. |
5,997 | Microcontrollers are used in automatically controlled products and devices, such as automobile engine control systems, implantable medical devices, remote controls, office machines, appliances, power tools, toys and other embedded systems. By reducing the size and cost compared to a design that uses a separate micropro... |
5,998 | Some microcontrollers may use four-bit words and operate at frequencies as low as 4 kHz for low power consumption . They generally have the ability to retain functionality while waiting for an event such as a button press or other interrupt; power consumption while sleeping may be just nanowatts, making many of them w... |
5,999 | The first multi-chip microprocessors, the Four-Phase Systems AL1 in 1969 and the Garrett AiResearch MP944 in 1970, were developed with multiple MOS LSI chips. The first single-chip microprocessor was the Intel 4004, released on a single MOS LSI chip in 1971. It was developed by Federico Faggin, using his silicon-gate M... |
6,000 | MOS Technology introduced its sub-$100 microprocessors in 1975, the 6501 and 6502. Their chief aim was to reduce this cost barrier but these microprocessors still required external support, memory, and peripheral chips which kept the total system cost in the hundreds of dollars. |
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