Chapter 15: What is RPC?
Remote Process Call (RPC) is a protocol that can request services to procedures on another computer in the network using this protocol. Since programs that use RPC do not have to know about network protocols that support communications, RPC improves the interoperability of programs. In RPC, issuing a request is a client, and a program that provides a service is a server.
Chapter 2: What is a domain name?
The Internet is the ocean of information, but where is this information stored? In fact, this information is stored on a computer called "site" around the world, each site is maintained by units with the site, the above information is published by the unit that maintains the site, which is also called "web page ".
In order to distinguish every site, you must assign a unique address for each site. This address is called "IP address". The IP address is also called URL (unique resource location, meaning "unified resource locator"), IP address It consists of four numbers from 0 to 255, such as 202.116.0.54, but these numbers are more difficult, so some people have invented a new method to replace this number, the "domain name" address, domain name by several English Word composition, such as www.jnu.edu.cn has certain significance, where CN represents China (China), EDU representative Education Network (EDUCATION), JNU, JINAN University, WWW represents the global network (or called World Wide Web, World WIDE WED, the entire domain name represents China Education Online and South University Site.
The domain name address and IP address represented by numbers are actually the same thing, but the appearance is different. When accessing a site, you can enter the IP address represented by the number, or enter its domain name address, here There is a problem with a domain name address and a corresponding IP address phase conversion. These information is actually stored on a computer called Domain Name Server (DNS) in the ISP. When you enter a domain name address, the domain name server searches its corresponding The IP address and then accesses the site represented by the address. Site address can be found on the magazine, newspapers and books of the computer, with more information on the Internet address on the Internet. From now on, you can collect some site domain names that you are interested in.
The domain name system of the Internet is set up for the IP address of the machine. The domain name system uses hierarchies, layers in a geographic domain or agency field. Writing is used in a circle to separate each level, divided into hierarchical fields. In the address representation of the machine, from the right to left, the highest domain name, the second high domain name, etc., the leftmost field, etc., the host name. For example, in bbs.jnu.edu.cn, the highest domain name is CN, and the second high domain name EDU is, the last domain is JNU, and the host is named BBS.
Chapter 27: What is DMA?
When we add a new sound card or other adapter card to your computer, the installer may remind us that we should choose a DMA channel. What DMA is DMA (DIRECT MEMORY Access), ie direct memory access, is a mechanism for quickly transferring data. Data delivery can be from an adapter card to memory, from a memory to an adapter or from a period of memory to another. The importance of DMA technology is that the participation of the CPU is not required when using it for data transfer. There are DMA controllers on each computer motherboard, usually computers, and store programs with ROMs on an adapter (such as a ROM on the floppy drive controller), which control DMA transfer data. Once the controller is initialized, the data begins transmitting, the DMA can detach from the CPU, independently complete the data transfer. In a transient time starting in DMA transmission, there is basically two processors working, one execute program code, one transfer data. Another advantage of using DMA transfer data is that data is transmitted directly between source addresses and destination addresses without the need for an intermediate medium. If you transfer one byte from an adaptation card to memory via the CPU, you need two steps. First, the CPU reads this byte from the adapter card to the internal register, and then transfer from the register to the appropriate address of the memory. The DMA controller simplifies these operations into one step, and its control signal on the bus is completed once. This greatly improves computer running speed and work efficiency. The computer has developed to this day, DMA is no longer used in memory to memory data transfer, because the CPU speed is very fast, doing this, it is better than using DMA, but to transfer data between adapter cards and memory, Still still non-DMA. To transfer data from an adapter card to memory, the DMA simultaneously triggers the bus from the adapted card read data bus (ie I / O read operation) and to memory write data. Activating I / O read operation is to put a data unit (usually one byte or one word) on the PC data bus, because the memory bus is also activated, and the data is simultaneously from the PC bus. Copy to memory. For each write operation, both the DMA controller controls the address bus, and the notification should write which memory should be written. The method of DMA control data is transmitted from memory to an adapter card similar to the above. For each unit data to be transmitted, the DMA controller activates the bus read memory and I / O write operations. The memory address is placed on the address bus, just like the adapter card to memory transmission data, the data bus is channel from the source address to the destination address. DMA receives the DMA request from the DMA request line (DREQ), and the forward image interrupt controller receives the interrupt request from the interrupt request line (IRQ). A typical data transfer from an adapted card to memory is made, first, the DMA controller is programmed, and the memory address to be reached and the number of bytes to be transmitted. When the adapter can start transmitting data, it will activate the DREQ line and communicate with the DMA controller. After obtaining the bus control with the CPU, the DMA controller outputs the memory address, transmits the control signal, so that one byte or word is read from the adapter and writes in the corresponding memory, then updates the memory address, pointing to the next byte (or Word) The address to be written, repeat the above operation until the data is transmitted. Different programming for the controller, you can implement single-byte transmission (ie, one DREQ signal is required to be transmitted) or block data transfer (ie, all data transfer only requires only one DREQ signal). If you want to insert an adapter card in your computer, and the adapter card uses DMA, usually the installer will allow you to select a DMA channel, set the DIP switch or jumper to set the DMA channel for the respective adapter.
Despite the theory, as long as it is not using the DREQ line, different adapter cards can share this line, but according to regular, we can arrange a DMA channel for each adapter card, so that it will not be guaranteed DMA conflicts occurred. The Schedule is the default allocation of DMA. Channel Function Channel Function O Idle 4 Used to Cascade DMA Controller 1 Free 5 Free 2 Floppy Disk 6 Free 3 Idle 7 You can see that the DMA Channels 2 and 4 have been occupied, in most microcomputers, channels 1, 3 5, 6 and 7 can be arbitrarily allocated by you. We usually record the allocation of DMA channels on your computer, so as to avoid two adapter cards to share a new channel when we add new hardware to your computer, resulting in conflicts. Mort8: What is IRQ?
IRQ is an interrupt, through interrupt, peripherals can acquire the CPU processing time. The following table shows the IRQ settings in the usual NT system.
Interrupt level Usually Uses Description 0 Clock 1 Keyboard 2 and IRQ 9 Level 3 COM2 or COM4 4 COM1 or COM3 5 LPT2 Because many users do not have a second parallel port, it is often idle, the sound card can be used to interrupt 6 floppy controller 7 LPT1 sound card can be used in this interrupt 8 real-time clock 9 and the IRQ 2 connection is directly connected to 2, sometimes notifying the software 9 意味 意 着 2 10 Not usually used for the NIC 11 is not used by the SCSI controller 12 PS / 2, bus mouse If the user does not have a PS / 2 or bus mouse, this interrupt free 13 coprocessor notifies the CPU coprocessor error 14 Hard disk controller If the user does not use the IDE hard disk, it can be used for other devices 15 Some computers will be allocated to the first interrupt Two IDE Controller i If the user does not use the second IDE hard disk controller, it can be used for other devices.
