1. Mercury delay line for memory device development
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 peak (1) and trough (0) of mechanical wave. The mechanical wave starts from one end of the mercury column, and a certain thickness of molten metal mercury travels from one end to the other through a vibrating diaphragm in the longitudinal direction, hence the name "mercury delay line". At the other end of the pipe, a sensor gets every point of information and feeds it back to the starting point. Imagine that mercury acquires and delays these data in order to store them. 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 affected by various environmental factors and is inaccurate.
1950, Dr. von Neumann designed the world's first computer EDVAC with the function of storing programs. Its main feature is that it uses binary and mercury delay line as memory, and instructions and programs can be stored in the computer.
1951March, 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. Tape for storage device development
For the first time, UNIVAC- I used tape drives as external storage. Firstly, the reliability of the system is improved by using parity check method and double operation circuit, and the automatic programming experiment is carried out for the first time.
Magnetic tape is one of the commonly used storage media with the lowest cost, the largest capacity and the highest degree of standardization in the development of all storage devices. It has good interchangeability and easy storage. In recent years, due to the adoption of coding technology with strong error correction ability and channel technology with strong reading and writing ability, the reliability and reading and writing speed of tape storage 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. Among them, two spiral scanning reading and writing methods are aimed at the DAT(4mm) tape drive at the workgroup level and the 8mm tape drive at the departmental level, and the other four are devices designed with data stream storage technology. They are single-head read-write mode for low-end applications, Travan and DC series with tape width of 1/4 inches, and multi-head read-write mode with tape width of 1/2 inches 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 under the control of drive management software, it can realize continuous backup, automatic tape search, intelligent recovery, real-time monitoring and statistics. The whole process of data storage and backup needs no manual intervention at all.
Tape library not only has much more data storage, 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. Remote data access, data storage backup or multi-tape library backup can be easily completed through tape mirroring technology, which is undoubtedly a good storage device for large-scale network applications such as data warehouse and ERP.
3. The drums of the development of storage devices
1953, with the development of memory devices, the first magnetic drum was applied to IBM 70 1 as memory. Magnetic drum uses magnetic materials coated on the surface of aluminum drum to store data. The drum rotates at high speed, so the access speed is fast. It uses saturated magnetic recording, from fixed head to floating head, from magnetic glue to electroplating continuous magnetic medium. All these laid the foundation for later disk storage.
The biggest disadvantage of magnetic 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. So as soon as the disk appeared, the drum was eliminated.
4. Core for storage device development
American physicist Wang An 1950 put forward the idea of making memory by using magnetic materials. Forrest Gump turned this idea into reality.
In order to realize magnetic core storage, Forrest needs a substance with a very clear magnetization threshold. He found an old German ceramic expert from a company producing ferrite converters for TV sets in New Jersey, and obtained specific magnetism by using molten iron ore and oxides.
Clear magnetization threshold is the key to design. This kind of wire mesh and wire core are woven on the metal mesh, which is called core storage. Its patent is very important to the development of computer. This scheme is reliable and stable. Magnetization is relatively permanent, so the stored data still exists after the system power is turned off. Because the magnetic field can be read at the speed of electrons, it makes interactive calculation possible. Furthermore, because it is a wire grid, any part of the memory array can be accessed, that is, different positions of the wire grid can store different data, and it can be accessed immediately by reading a string of bits at that position. This is called random access memory (RAM), which is an innovative concept of interactive computing in the development of storage devices. Forest transferred these patents to the Massachusetts Institute of Technology, which received150,000 to $20 million annually based on these patents.
IBM was the first company 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 1950s, all large and medium-sized computers have adopted this system. Core storage was the standard way of computer main memory from 1950s to 1970s.
5. Disks for storage device development.
The first hard disk memory in the world was invented by IBM in 1956, and the model is IBM 350 Ramac (random access method for accounting and control). The total capacity of this system is only 5MB, and 50 disks with a diameter of 24 inches are used. 1968, IBM company 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 shell to form the head disk assembly (HDA), which is isolated from the external environment and avoids dust pollution. Miniaturized, light and thin magnetic head slider is adopted, and the surface of the disk is coated with lubricant to realize contact start and stop. 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. At the end of 1980s, IBM made another great contribution to the development of storage devices, and invented MR (Magnetoresistive) magnetic head, which was quite sensitive to signal changes when reading data, and increased the storage density of magnetic disks by several times. 199 1 year, the 3.5-inch hard disk produced by IBM uses MR head, which makes the hard disk capacity 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 0/00GB per square inch/kloc, and it is the storage device with the largest capacity and cost performance. Therefore, among the external storage devices of computers, no other storage device can challenge its dominance in recent years. Hard disk is not only used in various computers and servers, but also the basic storage unit in disk array 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 size of hard disk is 1 inch, and the storage capacity has reached 4GB and 10GB. 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, 3.5-inch 1.44MB floppy disk has occupied the position of computer standard configuration for nearly 20 years, and then high-density transitional floppy disk and floppy drive products of 24MB, 100MB and 200MB appeared. 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 it will soon withdraw from the historical stage of storage equipment development.
6. CD-ROM for storage device development
CDs are mainly divided into read-only CDs and read-write CDs. Read-only means that the content on the CD is fixed, so it cannot be written or modified, and only the content can be read. The read-write type allows people to modify the contents of the CD, erase the original contents and write new ones. Microcomputer mainly uses CD-ROM, CD-R/W and DVD-ROM.
In the 1960s, researchers from Philips in the Netherlands began to use laser beams to record and replay information. Their research was successful in 1972 and put on the market in 1978. The original product was the well-known laser disc (LD) system.
From the birth of LD to CD-ROM for computer, it has gone through three stages: LD- laser disc, CD-DA laser disc and CD-ROM. The following briefly introduces the product characteristics of these three storage devices in different development stages.
LD- laser disk, commonly known as LCD, has a large diameter of 12 inch, and can record information on both sides, but the signal it records is analog. The processing mechanism of analog signal means that both analog TV image signal and analog sound signal are FM (frequency modulation), linearly superimposed, and then limited and amplified. The clipping signal is represented by a pit length of 0.5 micron wide.
Although CD-DA laser disc LD is successful, its development and production have fallen into expensive capital investment from the beginning because there is no unified standard in advance. 1982, Philips and Sony formulated the red book standard for CD-DA laser discs. Thus, a new type of CD was born. The recording method of CD-DA laser disc is different from 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). The advantage of digital recording instead of analog recording is that it is insensitive to interference and noise, and can correct errors caused by defects, scratches or pollution of the disk itself.
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, in order to use CD-DA as a computer's memory, two important problems must be solved, namely, to establish a data structure suitable for computer reading and writing, and to reduce the error rate of CD-DA from the existing 10-9 to below10-2, thus resulting in the CD-ROM yellow book standard. The core idea of the standard is to organize the data on the disk in the form of data blocks, and each block must have an address, so as to quickly find the data on the disk from hundreds of megabytes of storage space. In order to reduce the bit error rate, the scheme of increasing error detection and correction is adopted. Cyclic redundancy detection code (CRC) is used for error detection, and Reed Solomon code is used for error correction. The Yellow Book established the physical structure of the CD-ROM. In order to make it completely compatible on the computer, the file system standard of the CD-ROM, namely ISO 9660, was later formulated.
In the mid-1980s, optical disk storage devices developed rapidly, and new varieties such as WORM disk, magneto-optical disk (MO) and phase change disk (PCD) were introduced one after another. In 1990s, 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 to be launched soon. The laboratory is studying multi-layer and multi-layer optical discs and holographic storage optical discs, which are expected to be put on the market within five years.
7. Nano-storage for storage device development.
Nanometer is the unit of length, and the symbol is nm. 1 nm = 1 nm, and its length is about 10 atoms. Suppose that a hair has a diameter of 0.05 mm and is divided into 50,000 hairs on average in the radial direction, and the thickness of each hair is about 1nm. The main progress related to nano-storage is as follows.
From 65438 to 0998, the University of Minnesota and Princeton University successfully prepared quantum disks, which are nano-array systems composed of magnetic nanorods. A quantum disk is equivalent to our current 65438+100000 ~ 65438+100000 disks, but the energy consumption is reduced by 65438+100000 times.
1988, the French first discovered the giant magnetoresistance effect. By 1997, nanostructured devices based on the principle of giant magnetoresistance have been developed in the United States, which have broad application prospects in magnetic storage, magnetic memory, computer read-write heads and so on.
In September 2002, the research team of the University of Wisconsin announced that they had developed an atomic-level silicon storage material by manipulating a single atom at room temperature, and its information storage density was 6,543.8+0,000 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, this new storage material is built on the surface of silicon material. 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 orbits; Finally, with the help of the probe of scanning tunneling microscope, silicon atoms are extracted from these orderly arranged silicon atoms at intervals, the evacuated part represents "0" 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 room temperature at a time. More importantly, the spacing of silicon atom arrangement lines in the memory material is one atom. This ensures the atomic level of the memory material. Professor Helmsar said that the new silicon storage material has the same storage function as the current silicon storage material, but the difference is that the former is atomic volume, and the computer storage material made of it is smaller and denser. This will make the future computers smaller and the function of storing information more powerful.
These are the seven critical periods of the development of memory devices introduced to you in this paper.