SDRAM:SDRAM, namely synchronous dynamic random access memory, was once the most widely used memory type on PC. Even today, SDRAM still occupies a place in the market. Since it is "synchronous dynamic random access memory", it means that its working speed is synchronous with the system bus speed. SDRAM memory is divided into different specifications, such as PC66, PC 100 and PC 133. The numbers behind the specifications represent the maximum system bus speed at which the memory can work normally, such as PC 100, indicating that the memory can work synchronously in a computer with a system bus of 100MHz.
Synchronize with the system bus speed, that is, synchronize with the system clock, thus avoiding unnecessary waiting time and reducing data storage time. Synchronization also lets the memory controller know which clock pulse period is used for data request, so data can be transmitted as soon as the pulse rises. SDRAM uses 3.3 volt working voltage, 168Pin DIMM interface, and the bandwidth is 64 bits. SDRAM is not only used for memory, but also for video memory.
DDR SDRAM: Strictly speaking, DDR should be called DDR SDRAM, and people are used to calling it DDR. Some beginners often see DDR SDRAM and think it is SDRAM. DDR SDRAM is the abbreviation of double data rate SDRAM, which means double rate synchronous dynamic random access memory. DDR memory is developed on the basis of SDRAM memory and still uses SDRAM production system. Therefore, for memory manufacturers, DDR memory can be produced only by slightly improving the equipment for manufacturing ordinary SDRAM, which can effectively reduce the cost.
SDRAM only transmits data once in a clock cycle, and it transmits data in the rising cycle of the clock. DDR memory, on the other hand, transmits data twice in a clock cycle and can transmit data once in the rising and falling periods of the clock, so it is called dual-rate synchronous dynamic random access memory. DDR memory can achieve higher data transfer rate at the same bus frequency as SDRAM.
Compared with SDRAM, DDR adopts a more advanced synchronization circuit, which makes the main steps of specifying address and data transmission and output be executed independently and keep complete synchronization with CPU. DDR uses DLL (delay locked loop) technology. When the data is valid, the memory controller can use the data filter signal to accurately locate the data, output it every 16 times, and resynchronize the data from different memory modules. Essentially, DDL can double the speed of SDRAM without increasing the clock frequency. It allows reading data on the rising and falling edges of clock pulses, so it is twice as fast as standard SDRA.
There is not much difference between DDR and SDRAM in appearance and volume. They have the same size and the same pin distance. However, DDR has 184 pins, which is 16 more than SDRAM, and mainly contains new signals such as control, clock, power supply and grounding. DDR memory adopts SSTL2 standard supporting 2.5V voltage instead of LVTTL standard supporting 3.3V voltage used by SDRAM.
Detailed explanation of DDR2
RDRAM: RDRAM:RDRAM(RAMBUS DRAM) is a kind of memory developed by American RAMBUS Company. Different from DDR and SDRAM, it adopts serial data transmission mode. At the time of launch, because the transmission mode of memory was completely changed, it could not be guaranteed to be compatible with the original manufacturing process, and the memory manufacturer had to pay a certain patent fee in Ghana to produce RDRAM, plus its own manufacturing cost, which caused ordinary users to be unable to accept its high price from the moment it came out. At the same time, DDR has gradually become the mainstream with low price and good performance. Although RDRAM is strongly supported by Intel, it has never become the mainstream.
The data storage bit width of RDRAM is 16 bits, which is much lower than the 64 bits of DDR and SDRAM. But in terms of frequency, it is much higher than the two, reaching 400MHz or even higher. Similarly, data can be transmitted twice in a clock cycle, once in the rising and falling periods of the clock, and the memory bandwidth can reach1.6 gbyte/s. ..
The information in the ordinary DRAM line buffer will not be retained after being written back into the memory, while RDRAM has the characteristic of continuing to retain this information, so when accessing the memory, if there is target data in the line buffer, it can be used, thus realizing high-speed access. In addition, it can collect data and transmit it in the form of data packets, so as long as 24 clocks are used at the beginning, 1 byte can be read every 1 clock in the future. The length of data that can be read in one visit can reach 256 bytes.
Processor series model
CPU manufacturers will assign a series model to CPU products belonging to the same series, and the series model is an important symbol to distinguish CPU performance. Intel's main CPU series models are Pentium, Pentium Pro, Pentium II, Pentium III, Pentium 4, Pentium M, Pentium XXX (such as Pentium 530), Celeron II, Celeron D, Xeon and so on. AMD has K5, K6, K6-2, Duron, Athlon XP, Sempron, Athlon 64 and so on.
Processor core
Die, also called kernel, is the most important part of CPU. The chip protruding from the center of CPU is the core, which is made of monocrystalline silicon through a certain manufacturing process. All calculations, receiving/storing commands and processing data of CPU are executed by the kernel. All kinds of CPU cores have a fixed logical structure, and logical units such as first-level cache, second-level cache, execution unit, instruction-level unit and bus interface will have a scientific layout.
In order to manage the design, production and sales of CPU, CPU manufacturers will give corresponding codes to various CPU cores, which is the so-called CPU core type.
Different CPU (different series or the same series) will have different core types (such as Northwood of Pentium 4, Willamette, CXT of K6-2, ST-50 of K6-2+ and so on). ), even the same core will have different versions (for example, Northwood core is divided into B0 and C 1, etc. ). The core version is changed to correct some errors in the previous version. Each core type has its corresponding manufacturing process (such as 0.25um, 0. 18um, 0. 13um, 0.09um, etc.). ), core area (which is the key factor to determine the CPU cost, and the cost is basically proportional to the core area), core voltage, current, number of transistors, cache size at all levels, main frequency range, pipeline architecture and supported instruction sets (these two are the key factors to determine the actual performance and work efficiency of CPU), power consumption and calorific value, and packaging methods (such as S.E.P, PGA, FC-PGA, FC-PGA). ), and interface types (such as Socket3772) Socket A, Socket 478, Socket T, Slot 1, Socket 940, etc. ), FSB, etc. So the core type determines the performance of CPU to some extent.
Generally speaking, the new core type often has better performance than the old core type (for example, the performance of Pentium 4 1.8GHz of Northwood core with the same frequency is higher than that of Pentium 4 1.8 GHz of Willamette core), but this is not absolute. This usually happens when a new core type has just been introduced, which may be caused by imperfect technology or immature new architecture and manufacturing technology. For example, the actual performance of Pentium 4 with Willamette Socket 423 interface in the early days is not as good as Pentium III and Celeron with Tualatin Socket 370 interface, and the actual performance of Pentium 4 with low frequency Prescott kernel is not as good as that with high frequency. However, with the progress of technology and the continuous improvement and perfection of the new core by CPU manufacturers, the performance of the new core product will inevitably surpass that of the old core product.
The development direction of CPU core is lower voltage, lower power consumption, more advanced manufacturing technology, integration of more transistors, smaller core area (which will reduce the production cost of CPU and ultimately lower the sales price of CPU), more advanced pipeline architecture and more instruction sets, higher front-end bus frequency, and integration of more functions (such as integrated memory controller, etc.). ) and dual-core multi-core (that is, there are two or more CPUs in 1) The most significant thing for ordinary consumers is that they can buy more powerful CPUs at lower prices.
Front end bus
A bus is a set of transmission lines that transmit information from one or more source components to one or more destination components. Generally speaking, it is a common connection between multiple components, which is used to transfer information between components. People often use MHz to describe the bus frequency. There are many kinds of buses. The English name of the front-end bus is Front Side Bus, which is usually expressed by FSB. It is a bus connecting CPU and Northbridge chip. The front-end bus frequency of computer is determined by CPU and Northbridge chip.
The north bridge chip is responsible for contacting the components with the largest data throughput such as memory and graphics card, and connecting with the south bridge chip. The CPU is connected to the Northbridge chip through the front-end bus (FSB), and then exchanges data with the memory and graphics card through the Northbridge chip. The front-end bus is the most important channel for CPU to exchange data with the outside world, so the data transmission ability of the front-end bus plays a great role in the overall performance of the computer. If there is no fast front-end bus, no matter how strong the CPU is, it can't obviously improve the overall speed of the computer. The maximum bandwidth of data transmission depends on the width and transmission frequency of all data transmitted at the same time, that is, data bandwidth = (bus frequency × data bit width) ÷8. At present, the front-end bus frequencies that can be realized on a PC are 266MHz, 333MHz, 400MHz, 533MHz, 800MHz, and the highest is 1066MHz. The greater the frequency of the front-end bus, the greater the data transmission capacity between the CPU and the North Bridge chip, and the better the functions of the CPU can be brought into play. At present, CPU technology is developing rapidly and the operation speed is increasing rapidly. A large enough front-end bus can ensure enough data for CPU, while a low front-end bus will not supply enough data for CPU, thus limiting the performance of CPU and becoming the bottleneck of the system.
The difference between external frequency and front-end bus frequency: the speed of front-end bus refers to the bus speed between CPU and Northbridge chip, which more substantially indicates the speed of data transmission between CPU and the outside world. The concept of external frequency is based on the oscillation speed of digital pulse signal, that is to say, 100MHz external frequency means that digital pulse signal oscillates 1 100 million times per second, which has a greater impact on the frequency of PCI and other buses. The two concepts of front-end bus and external frequency are easily confused, because for a long time before (mainly before and just after Pentium 4 appeared), the front-end bus frequency and external frequency were the same, so they were often called external frequency directly, which eventually caused such misunderstanding. With the development of computer technology, people find that the front-end bus frequency needs to be higher than the external frequency, so QDR (Quadruple Data Rate) technology or other similar technologies are adopted to achieve this goal. The principle of these technologies is similar to 2X or 4X of AGP, which makes the frequency of the front-end bus 2 times, 4 times or even higher than the external frequency. From then on, people began to pay attention to the difference between front-end bus and external frequency. At present, mainstream products adopt these technologies.
Expansion slots are slots on the motherboard for fixing expansion cards and connecting them to the system bus, also known as expansion slots and expansion slots. Expansion slots are a way to add or enhance computer features and functions. For example, if you are not satisfied with the performance of the motherboard integrated graphics card, you can increase the independent graphics card to enhance the display performance; If you are not satisfied with the sound quality of the onboard sound card, you can add a separate sound card to enhance the sound effect; Motherboards that do not support USB2.0 or IEEE 1394 can obtain this function by adding corresponding USB2.0 expansion cards or IEEE 1394 expansion cards.
At present, the main types of expansion slots are ISA, PCI, AGP, CNR, AMR, ACR, relatively rare WI-FI, VXB, PCMCIA for notebook computers and so on. There are MCA slots, EISA slots and VESA slots, which have appeared in history and have long been eliminated. The mainstream expansion slot in the future is PCI Express slot.
PCI slot is an expansion slot based on PCI local bus (Pedpherd Component Interconnect), which is generally ivory in color and located below AGP slot and above ISA slot on motherboard. Its bit width is 32 bits or 64 bits, its working frequency is 33MHz, and its maximum data transmission rate is 133 MB/ s (32 bits) and 266 MB/ s (64 bits). Card card, sound card, network card, built-in modem, built-in ADSL modem, USB2.0 card, IEEE 1394 card, IDE interface card, RAID card, TV card, video capture card and other expansion cards. PCI slot is the main expansion slot of motherboard. By plugging in different expansion cards, you can get almost all the functions that computers can achieve at present, which is a veritable "universal" expansion slot.
AGP(Accelerated Graphics Port) is developed on the basis of PCI bus, which is mainly optimized for graphic display and specially used for graphic display cards. The AGP standard has also developed for several years, from the initial AGP 1.0 and AGP2.0 to the present AGP 3.0. If divided by multiple speeds, it has mainly experienced AGP 1X, AGP 2X, AGP 4X and AGP PRO, and the latest version is AGP 3.0, namely AGP 8X. The transmission rate of AGP 8X can reach 2. 1GB/s, which is twice that of AGP 4X. AGP slots are usually brown (the purpose of distinguishing the above three interfaces with different colors is to facilitate user identification). It should be noted that they are not in the same horizontal position as PCI and ISA slots, but embedded, which prevents PCI and ISA cards from being inserted. Of course, the AGP slot structure is completely different from PCI and ISA, so it is impossible to insert it wrong.
PCI-Express is the latest bus and interface standard. Its original name is "3GIO", which was put forward by Intel Corporation. Obviously, what Intel means is that it represents the next generation I/O interface standard. After being certified by PCI-SIG, it was renamed as "PCI-Express". This new standard will completely replace the existing PCI and AGP, and finally realize the unification of bus standards. Its main advantage is its high data transmission rate, which can reach above 10GB/s at present, and its development potential is considerable. PCI Express also has many specifications, from PCI Express 1X to PCI Express 16X, which can meet the needs of low-speed equipment and high-speed equipment at present and in the future. Intel's i9 15 and i925 series chipsets can support PCI Express. Of course, it will take a long time to completely replace PCI and AGP, just like when PCI replaces ISA, there will be a transition process.
When purchasing motherboard products, the type and quantity of expansion slots are important indicators to determine the purchase. Having a variety of types and a sufficient number of expansion slots means that there will be enough upgrades and equipment expansion in the future, otherwise there will be huge obstacles to future upgrades and equipment expansion. This is especially important for beginners. For example, if you are dissatisfied with the game performance of the integrated motherboard and want to upgrade to a discrete graphics card, you find that there is no AGP slot on the motherboard; I want to add a video capture card, but I found that all the PCI slots used are full. However, the more expansion slots, the better. Too many slots will increase the cost of the motherboard and increase the purchase cost of users. And too many slots have no effect on many users. For example, an office computer that only needs to do word processing and surf the Internet, equipped with six PCI slots and a discrete graphics card, is a typical waste of resources. This kind of computer can fully meet the use requirements only by using the integrated micro ATX motherboard. Therefore, in the purchase of specific products, we should choose according to our own needs, and the one that suits us is the best.