1. Mercury delay line
Mercury delay line is based on the fact that mercury is both a liquid and a conductor at room temperature, and each bit of data is represented by the peaks (1) and valleys () of mechanical waves. The mechanical wave starts from one end of the mercury column, and a certain thickness of molten metal mercury is transmitted from one end to the other along the longitudinal direction through a vibrating diaphragm, so it is named "mercury delay line". At the other end of the tube, a sensor gets every bit of information and feeds it back to the starting point. Imagine that mercury acquires and delays these data so that they can be stored. This process is a wonderful combination of machinery and electronics. The disadvantage is that due to the limitation of environmental conditions, this memory method will be influenced by various environmental factors and will not be accurate.
in p>195, the world's first computer with the function of storing programs, EDVAC, was developed by Feng? Dr. Neumann led the design. Its main feature is that it uses binary, uses mercury delay line as memory, and instructions and programs can be stored in the computer.
in March p>1951, the first universal automatic computer UNIVAC-I designed by Moakley and eckert, the main designers of ENIAC, was put into use. It can not only do scientific calculation, but also do data processing.
2. Magnetic tape
UNIVAC-I uses a tape drive as external memory for the first time. At first, it uses parity check method and double operation circuit to improve the reliability of the system, and the automatic programming experiment is carried out first.
magnetic tape is one of the commonly used storage media with the lowest cost, the largest capacity and the highest degree of standardization. It has good interchangeability and easy storage. In recent years, due to the adoption of coding technology with high error correction ability and channel technology of write-and-read ability, the reliability of tape storage and the speed of reading and writing have been greatly improved. According to the working principle of reading and writing magnetic tape, it can be divided into spiral scanning technology, linear recording (data stream) technology, DLT technology and more advanced LTO technology.
according to the working principle of reading and writing tapes, tape drives can be divided into six specifications. Two of them are DAT(4mm) tape drives for workgroup level and 8mm tape drives for department level, and the other four are devices designed with data stream storage technology. They are Travan and DC series with single head reading and writing mode and tape width of 1/4 inch for low-end applications, and DLT and IBM's 348/348 with multi-head reading and writing mode and tape width of 1/2 inch for high-end applications.
Tape library is a tape-based backup system, which can provide the same basic automatic backup and data recovery functions, but at the same time it has more advanced technical characteristics. Its storage capacity can reach hundreds of PB, and it can realize continuous backup, automatic tape search, intelligent recovery, real-time monitoring and statistics under the control of drive management software. The whole data storage and backup process is completely free from manual intervention.
the tape library not only has a much larger data storage capacity, but also has incomparable advantages in backup efficiency and labor occupation. In the network system, the tape library can form a network storage system through SAN(Storage Area Network) system, which provides a strong guarantee for enterprise storage. It is easy to complete remote data access, data storage backup or multi-tape library backup through tape mirroring technology, and it is undoubtedly a good storage device for large-scale network applications such as data warehouse and ERP.
3. Magnetic Drum
In p>1953, the first magnetic drum was applied to IBM 71, which was used as an internal memory. Magnetic drum uses the magnetic material coated on the surface of aluminum drum to store data. The drum rotates at a high speed, so the access speed is fast. It uses saturated magnetic recording, from fixed magnetic head to floating magnetic head, from magnetic glue to electroplated continuous magnetic medium. All these laid the foundation for the later disk storage.
The biggest disadvantage of the drum is its low utilization rate. A large cylinder has only one surface layer for storage, while both sides of the disk are used for storage, obviously the utilization rate is much higher. Therefore, when the disk appeared, the drum was eliminated.
4. Magnetic core
In 195, the American physicist Wang An put forward the idea of making memory by using magnetic materials. Forrest turned this idea into reality.
in order to realize magnetic core storage, Forrester needs a substance, which should have a very clear magnetization threshold. He found an old German ceramic expert from a company that produces ferrite converters for TV sets in New Jersey, and obtained specific magnetic properties by using molten iron ore and oxides.
a clear threshold for magnetization is the key to design. The grid and core of this kind of wire are woven on the wire net, which is called core storage. Its patent is very important for the development of computers. This scheme is reliable and stable. Magnetization is relatively permanent, so the stored data remains after the power of the system is turned off. Since magnetic fields can be read at the speed of electrons, it makes interactive calculation possible. Furthermore, because it is a wire grid, any part of the storage array can be accessed, that is, different data can be stored in different positions of the wire grid, and it can be accessed immediately by reading a bunch of bits at the position. This is called random access memory (RAM), which is an innovative concept of interactive computing. Forrest transferred these patents to MIT, which received $15 million to $2 million each year.
IBM was the first to obtain these patent licenses, and IBM finally got a commercial contract to install Cyclone in the North American defense military base. More importantly, since the 195s, all large and medium-sized computers have adopted this system. Magnetic core storage has been the standard way of computer main memory from 195s and 196s until the early 197s.
5. Disks
The world's first hard disk memory was invented by IBM in 1956, and its model is IBM 35 RAMAC (Random Access Method of Accounting and Control). The total capacity of this system is only 5MB, and 5 disks with a diameter of 24 inches are used. In 1968, IBM put forward "Winchester /Winchester" technology, the key point of which is to seal the high-speed rotating disk, magnetic head and its seek mechanism in a dust-free enclosure, forming a head-disk assembly (HDA), which is isolated from the external environment and avoids dust pollution. The miniature and frivolous magnetic head slider is adopted, and the surface of the disk is coated with lubricant, which is the most modern hard disks. In 1979, IBM invented the thin-film magnetic head, which further reduced the weight of the magnetic head and made it possible to have faster access speed and higher storage density. In the late 198s, IBM made another great contribution to the disk technology, and invented the MR(Magneto Resistive) magnetic head, which is quite sensitive to signal changes when reading data, making the storage density of the disk dozens of times higher than before. In 1991, the 3.5-inch hard disk produced by IBM used MR head, which made the capacity of the hard disk reach 1GB for the first time. Since then, the capacity of the hard disk has entered the order of GB. IBM also invented PRML (Partial Response Maximum Likelihood) signal reading technology, which greatly improved the sensitivity of signal detection, thus greatly improving the recording density.
at present, the area density of hard disk has reached more than 1Gb per square inch, which is a storage device with the largest capacity and cost performance. Therefore, among the external storage devices of computers, there is no other storage device that can challenge its dominant position in recent years. Hard disk is not only used in various computers and servers, but also a basic storage unit in disk arrays and various network storage systems. It is worth noting that the appearance and rapid development of micro hard disk in recent years provide an ideal storage medium for mobile storage. In the field of large-capacity mobile storage, which is difficult for flash memory chips to bear, micro hard disks can show their talents. At present, the storage capacity of 1-inch hard disk has reached 4GB, and 1GB 1-inch hard disk will be available soon. Micro hard disks are widely used in digital cameras, MP3 devices and various handheld electronic devices.
another disk storage device is floppy disk, which is mainly used for data exchange and small-capacity backup, from the early 8-inch floppy disk, 5.25-inch floppy disk to 3.5-inch floppy disk. Among them, the 3.5-inch 1.44MB floppy disk has occupied the standard configuration position of computers for nearly 2 years, and then there have been 24MB, 1MB and 2MB high-density transitional floppy disks and floppy drive products. However, due to the emergence of flash memory with USB interface, the dominant position of floppy disk as data exchange and small-capacity backup has been shaken and will soon withdraw from the historical stage.
6. CDs
CDs are mainly divided into read-only CDs and read-write CDs. Read-only type means that the contents on the CD are fixed and cannot be written or modified, only the contents can be read. The read-write type allows people to modify the contents of the CD, and can erase the original contents and write new ones. There are mainly CD-ROM, CD-R/W and DVD-ROM used in microcomputers.
in the 196s, researchers from Philips in the Netherlands began to use laser beams to record and replay information. In 1972, their research was successful and put on the market in 1978. The original product is the well-known Laser Vision Disc (LD) system.
from the birth of LD to CD-ROM for computer, it has gone through three stages, namely LD- laser disc, CD-DA laser disc and CD-ROM. The following briefly introduces the product characteristics of these three stages.
LD- laser disc, commonly known as LCD, has a large diameter of 12 inches, and can record information on both sides, but the signal it records is analog. The processing mechanism of analog signals means that both analog TV image signals and analog sound signals are subjected to FM(Frequency Modulation) frequency modulation, linear superposition, and then amplitude limiting amplification. The clipped signal is represented by the pit length of .5 micron wide.
although CD-da laser disc LD has been successful, its development and production have been plunged into expensive capital investment from the beginning because there is no unified standard in advance. In 1982, the Red Book standard for CD- DA laser discs was formulated by Philips and Sony. Thus, a new type of CD was born. The recording method of CD-DA laser disc is different from that of LD system. The CD-DA laser disc system firstly digitizes the analog audio signal by PCM (Pulse Code Modulation), and then records it on the disc after EMF (8 ~ 14 bit modulation) coding. The advantage of digital recording instead of analog recording is that it is insensitive to interference and noise, and errors caused by defects, scratches or contamination of the disk itself can be corrected.
after the success of CD-DA system, Philips and Sony naturally thought of using CD-da as a large-capacity read-only memory of computers. However, if CD-DA is to be used as a computer's memory, two important problems must be solved, namely, establishing the data structure of the disk suitable for computer reading and writing, and the error rate of CD-DA must be reduced from the existing 1-9 to below 1-12, thus resulting in the Yellow Book standard of CD- ROM. The core idea of this standard is that the data on the disk is organized in the form of data blocks, and each block must have an address, so that the data on the disk can be quickly found from hundreds of megabytes of storage space. In order to reduce the bit error rate, a scheme of adding error detection and error correction is adopted. Error detection adopts cyclic redundancy detection code, so-called CRC, and error correction adopts Reed Solomon code. The Yellow Book established the physical structure of CD-ROM, and in order to make it fully compatible on computers, it later formulated the file system standard of CD-ROM, namely ISO 966.
in the mid-198s, the development of optical discs was very rapid, and new varieties such as WORM disc, magneto-optical disc (MO) and Phase Change Disk (PCD) were introduced successively. In 199s, DVD-ROM, CD-R and CD-R/W began to appear and become popular, and now they have become the standard storage devices of computers.
optical disc technology is further developing towards high density, and Blu-ray disc is the next generation of high density optical disc that will be launched soon. Multi-layer and multi-level optical disks and holographic storage optical disks are being studied in the laboratory and are expected to be put on the market within five years.
7. Nano storage
Nano is a unit of length with the symbol nm. 1 nanometer =1 nanometer, which is about 1 atoms long. Suppose a hair has a diameter of .5 mm, and it is divided into 5, pieces on average in the radial direction, and the thickness of each piece is about 1 nanometer. The main progress related to nano-storage is as follows.
In p>1998, the University of Minnesota and Princeton University in the United States successfully prepared quantum disks, which are nano-array systems composed of magnetic nanorods. A quantum disk is equivalent to our present 1, ~ 1 million disks, but the energy consumption is reduced by 1, times.
In p>1988, the French first discovered the giant magnetoresistance effect. By 1997, nano-structured devices based on the principle of giant magnetoresistance had appeared in the United States, which had broad application prospects in magnetic storage, magnetic memory and computer read-write heads.
In September, 22, the research team of the University of Wisconsin announced that they had developed an atomic-level silicon memory material by manipulating a single atom at room temperature, and its storage density was 1 million times that of the current optical disk. This is a great progress in the research of nano-storage materials technology. According to the research report published in the journal Nanotechnology, the new memory materials are built on the surface of silicon materials. The researchers first sublimated gold on the surface of silicon material to form accurate atomic orbits; Then sublimate the silicon element and arrange it according to the above atomic orbit; Finally, with the help of the probe of scanning tunneling microscope, silicon atoms are extracted from these orderly arranged silicon atoms at intervals, and the evacuated part represents "" and the remaining silicon atoms represent "1", thus forming an atomic-level memory material equivalent to the function of a computer transistor. The whole experimental study was carried out at room temperature. Professor Helmsar, the head of the research team, said that it is not easy to manipulate a batch of atoms at a time at room temperature. More importantly, the spacing in the silicon atom arrangement line in the memory material is one atom size. This ensures the atomic level of memory materials. Professor Helmsar said that the new silicon memory material has the same storage function as the current silicon memory material, but the difference is that the former is atomic volume, and the computer memory material made from it is smaller and denser. This will enable future computers to be miniaturized,