Analysis of exam questions for senior programmers

Analysis of exam questions for senior programmers -- Basic computer hardware knowledge (advanced programmer level) A total of 15 basic hardware knowledge questions for Senior Programmer qualification and level test questions cover: 1. random memory type features. 2. Virtual Memory features and working principles. 3. Data Reliability coding CRC and working principle. 4. Streamline the features of the instruction computer. I. Types and features of primary storage (Subject 9) The primary storage is used to store the commands and data required by running programs. Is a component that the CPU can directly access. The main requirement of the host for primary storage is high speed. Primary storage usually includes random read/write Memory RAM and read-only memory Rom. 1. Random read/write, as long as the memory chip that keeps its storage content unchanged is called static random read/write memory SRAM, its unit storage principle is similar to the trigger. 2. Random read/write, but the chip that stores information must be refresh constantly. It is called dynamic random read/write Memory DRAM, which is made up of dynamic MOS circuits. Capacitor charging is used to store data, but because the circuit itself has always had a leakage, it is necessary to regularly recharge the data to maintain its storage. Note that DRAM must be refreshed on a regular basis even when it is continuously powered. However, such a refresh is automatically performed without human intervention. 3. The memory used by the manufacturer to write data before the product leaves the factory is called read-only storage Rom. Users cannot change the content, which is often used to store the fixed program. 4. the user feels inconvenient when using the Rom. Sometimes, when occasionally changing the ROM content, the EPROM can be used as a erasable programmable read-only memory. However, each erasure requires direct ultraviolet radiation to this chip ~ 20 minutes, and special devices must be used to write data. Therefore, it is still read-only during machine running. 5. A new type of flash memory FM is available. It features that a signal can be used to quickly erase part or all of the chip content within a few seconds, but the specified unit (byte) cannot be erased separately. Ii. Virtual Memory (question 10) 1. Primary storage features fast but small capacity, and direct CPU access. External storage features high capacity and slow speed, and the CPU cannot be accessed directly. User programs and data are usually stored in external storage. Therefore, it is often necessary to send data between the primary and external storage. It is inconvenient for users to intervene in scheduling. The virtual memory is used to solve this problem, so that users feel that they can directly access the entire internal and external storage space without user intervention. Therefore, the external memory (hard disk) with a large capacity and fast speed becomes the main component of the virtual memory. 2. The scheduling method of the data in the hard disk in the virtual memory is similar to that of the master memory. That is, the frequently accessed data is transferred to the high-speed primary storage for storage. Unnecessary data is sent back to the hard disk using a replacement algorithm. These call-in and call-out operations are automatically completed by the virtual memory. 3. user programs use virtual access to the entire virtual space, while command execution can only access the primary storage space. Therefore, you must perform real-world address translation to transfer the content of the unit that is not in the primary storage to a certain unit in the primary storage and then access it based on the converted real address. 4. in virtual storage, real-world address translation is the key. In order to improve the conversion speed, hardware usually supports this conversion, that is, the negative page is placed in the connected memory, and the connected memory is accessed by content, directly find whether you want to access the virtual page number in the connected storage to obtain the relevant real page number. Iii. Data Reliability coding CRC (11th) 1. the reliability of data stored and transmitted on the computer directly affects the computer's reliability. It is very important to identify and correct the generated data errors in a timely manner through coding technology. CRC is a common error code, that is, the Cyclic Redundancy correction code. 2. The modulo division is used to generate CRC verification codes. In the model 2 operation, the bitwise operation is performed. The addition and subtraction of Modulo 2 do not generate bitwise AND bitwise. The Modulo-didivision algorithm uses the Modulo-disubtraction method to calculate the remainder. If the maximum bit of the remainder is "1", the operator "1"; otherwise, the operator "0 ", when each operator has one digit, the remainder is reduced by one until the remainder is less than the divisor. 3. if the generated polynomial g (x) = X4 (4 Power) + X3 (3 power) + x + 1 original packet is 1100 1010 101, the CRC code is calculated as follows: Add the remaining number 0011 to the end of the message to obtain its CRC code 1100 1010101 0011. Therefore, the other three codes shown in the answer are incorrect. This question requires understanding of the CRC Code Generation Principle and the modulo division. 4. Verification Principle When a CRC code is received, the generated polynomial is used to remove the CRC code. If the remainder is 0, the transfer is correct. If the remainder is not 0, a transfer error occurs. You can identify the Error Based on the remainder, and change the bitwise to reverse. Therefore, CRC code can be found to correct a dislocation. CRC can be used to detect sudden errors that are less than or equal to the length of the check bit. The operating system and compilation optimization are taken into account in the computer command system of the server-defined language (PROTEUS). Therefore, the compilation process is simpler. Author profile: Xie Shuyun, a professor at the computer department of Tsinghua University, and Vice President of the Software Testing Training Department of the China Software Industry Association. In 1959, Tsinghua University Graduated from the Automatic Control Department of Computer Science. I have stayed in school and have been engaged in teaching and scientific research on the computer system structure for a long time. I have presided over a number of "" national key science and technology projects and National Natural Science Foundation projects, he has won the second prize for National and ministerial scientific and technological progress.