2015 first half software designer Test Center, difficulty

Memory:

Advanced memory capacity is generally small, while low-level memory capacity is large.

Register:

Part of the central processor is a high-speed storage unit with limited storage capacity that can be used to hold instructions, data, and addresses. It's CPU-bound.

Is the component part of the CPU. Registers are high-speed storage parts with limited storage capacity that can be used to hold instructions, data and addresses. In the control unit of the central processor, the registers included are the instruction register (IR) and the program counter (PC). In the arithmetic and logic parts of the central processing Unit, the registers included are accumulators (ACC).

Cache caches:

The parts that are set up to compensate for the difference between CPU and memory, not every CPU (the obvious example is the difference between Pentium and some Celeron)

Buffer memory is a small but high-speed memory that sits between the CPU and the main memory. Because the CPU speed is much higher than the main memory, the CPU accesses the data directly from the memory to wait for a certain period of time, the cache holds the CPU just used or recycled part of the data, when the CPU re-use the part of the data can be directly called from the cache, which reduces the CPU waiting time, Improve the efficiency of the system. The cache is also divided into one-level cache (L1 cache) and level two cache (L2 cache), L1 cache is integrated within the CPU, L2 cache is usually soldered to the motherboard, and is now integrated into the CPU, with a common capacity of 256KB or 512KB L2 Cache.

　　

　　

Complement:

A positive complement is its own

The complement of a negative number is on the basis of its original code, the sign bit is unchanged, the rest of you take the counter, the last +1. (That is, on the basis of the anti-code +1)

　　

Cache: Cache

　　

1. Direct Image:Cache can only hold 0--n block and only one per block (cannot exist two block 0), if 1 zone 0 block into the Cache Of the 0 , then no other area of 0 can be stored in the Cache. So it is known that the block number can determine the area code! Solid only need to compare the area code is equal!

　　Advantages: The address image is simple, data access, just check the area code is equal, so you can get faster access speed, simple hardware equipment.

Cons: Frequent replacement operations, low hit ratio.

The probability of block collisions is higher in this way, and the cache hit rate drops sharply when the sequential round-trip accesses data from two conflicting blocks, because there are other free blocks in the cache that cannot be applied because of the fixed address image relationship.

　　

2. Fully connected Image: both main memory and Cahce memory are divided into blocks with the same capacity. Allows any block in main memory to be transferred into any piece of space in the cache memory.

　　Advantages: High hit ratio, cache storage space utilization is high.

Disadvantage: When accessing related memory, it should be compared with all content, low speed, high cost, and therefore less application.

In this way, block collisions occur only when the blocks in the cache are full, so the probability of block collisions is low and the cache hit rate is high, but the implementation is complex.

　　

3. Group-linked Image: The first two ways of compromise, the C ache will be divided into groups. The group adopts the direct image method and the block adopts the all-connected method. The group number is determined by the direct image, and the block number in the Cache is determined in the group by using the full-phase image method.

　　Advantages: The collision probability of block is comparatively low, the utilization rate of block is greatly increased, and the block failure ratio is obviously reduced.

Disadvantage: The difficulty and cost of implementation is higher than the direct image method.

It is simpler to determine the block hit and replace algorithm than the full-phase method, the probability of block collision is lower than the direct image, and its hit ratio is between the direct image and the full-associated image mode.

　　

Storage Management

Page-type storage:

Divides the address space of a process into several regions of equal size, called pages. Accordingly, the main memory space is divided into a number of physical blocks of the same size as the page. When you allocate main memory for a process, several pages in the process are loaded into nonadjacent blocks, respectively.

Based on the page number in the logical address compared to the page table length register, if the page number is greater than or equal to the page table length register, the access is out of bounds, resulting in an out-of-bounds interrupt. If there is no cross-border, the location in the page table entry is calculated based on the initial address and page number in the page table register, the physical block number of the page is loaded, the physical address register is placed, and the page addresses are unchanged.

Advantages: The page table is transparent to the programmer, the address transforms quickly, the operation is simple;

Disadvantage: Each page is not a separate module of the program, it is not easy to implement program and data protection.

　　

Segment-Type storage:

　　　　The address space of the job is divided into several segments, each of which is a complete set of logical information, such as a main program segment, a subroutine segment, a data segment, and a stack segment, each with its own name, which is a contiguous address space starting at 0 and varying in length.

　　　　Advantages: Eliminate the memory fraction, easy to implement storage protection, easy to program dynamic assembly;

Disadvantage: The transfer operation is complex, the address transformation speed is slower than the page storage management.

　　　　

Segment-page Storage:

First divides the whole main memory into the equal size storage block, divides the user program into several segments according to the program logical relation, and assigns each segment the paragraph name, then divides each paragraph into several pages, the page is the unit discrete allocation.

Disadvantages:

　　　　1, section page management combines the two ways of paragraph and page, and make full use of their advantages.

　　　　2, the Segment-page virtual memory management scheme has the characteristics of small space waste, easy storage sharing, easy storage protection and dynamic connection.

3, but due to the increase in management software, complexity and overhead also increased, the need for hardware and occupied content has also increased, resulting in a significant decrease in execution speed.

　　　　　　　

Contrast:

　　　　

Bus bandwidth Calculation

Clock frequency: "Several cycles per second"

Bus width: This bus can transmit data at the same time as the number of vehicles allowed to walk side by

Bus Bandwidth: The total amount of data that this bus can transmit per unit of time, which is equal to the product of the bus bit width and clock frequency.

Bus bandwidth = (bus bit width/8) * Bus clock

Pipeline Technology

A common and effective technique for increasing processor throughput and increasing processor speed without the need to add too much hardware

Classification: Computing Pipeline (each segment and a unified clock synchronization), command line (need to constantly visit, the time is uncertain, it is difficult to use a unified clock to control the work of each section)

Characteristics:

1. Each sub-process is called "Level", "segment"; "Level" is called the "depth" of the pipeline

2. Need to have "pass time, Loading time", then enter the stable state

3. Can not shorten the corresponding time of a single task, increase throughput rate

4. is limited by the speed of the slowest pipeline segment. Therefore, the time required for each function segment should be as equal as possible

5. Suitable for a large number of repetitive processing processes

6. Multi-tasking parallel processing

7. To achieve the function of sub-process as much as possible, to avoid the unequal processing of the bottleneck, forming a pipeline flow

8. When the instruction stream is not executed sequentially, the process of running the flow is interrupted. The process of forming flowing water requires "passing time". To improve efficiency

The maximum throughput depends on the time required for the slowest part of the pipeline, so this segment is called a pipeline bottleneck

Eliminate bottlenecks: Subdivide bottleneck segments; repeat set bottleneck segments

Techniques for improving instruction-level parallelism

1. Disorderly execution:

Skip the relevant instructions to perform the subsequent irrelevant instructions so that the order of execution of the instructions is no longer in the order of the original program

Requires the command scheduling algorithm to ensure that the program's running results are the same as the results in sequential execution

The order in which the tasks flow out from the pipeline is different from the order of flow into the pipeline, also known as disorderly flow or wrong order flow. Performance will degrade.

How it works: In the event of data correlation, allow no data related subsequent instructions to enter the function segment occupied by the relevant instructions, and go beyond the relevant instructions to continue to flow forward

Correlation: The dependencies that exist between directives.
Risk: An instruction pipeline anomaly caused by a related problem

Risk-taking when using chaotic flow

2. Register Rename

3. Speculative execution

Solve the problem:

1. Conflict of Visits

2. Pipeline related processing: number-related, transfer-related, interrupt processing

Telnet protocol:

1) Telnet (telecommunication Network Protocol):

Telnet is an option negotiation mechanism between the client and the server, enabling both parties to communicate with specific functions.

2) Rlogin

The option negotiation mechanism is omitted because the client process and the server process have already known the other's operating system type beforehand.

In general, it is similar to the Telnet protocol, but the internal implementation is relatively straightforward.

3) SSH (Secure Shell)

Advantages: (1) SSH is a reliable protocol for remote logins and other security services, it employs a data encryption mechanism to prevent DNS spoofing and IP spoofing. (2) The transmitted data is compressed , so the transmission speed is relatively faster.

SSH protocol is a security protocol based on the application layer and transport layer, which consists of three parts: (1) The contents of the Transport layer protocol, providing authentication, data integrity check and other functions. (2) The User authentication protocol layer, it runs in the transmission layer, mainly realizes the communication process the identity authentication, the authentication way includes the password authentication, the key authentication and so on. (3) The Connection protocol layer, is responsible for allocating the encrypted channel to the logical channel, runs at the User authentication protocol layer.

Extended:

ARP (Address Resolution Protocol): Addresses Resolution Protocol, which is a TCP/IP protocol that obtains physical addresses based on IP addresses

WEP (Wired equivalent Privacy), the Wired Equivalent Privacy (WEP) protocol is a way to encrypt data transmitted wirelessly between two devices to prevent illegal users from eavesdropping or hacking into wireless networks

Network security:

1. Physical Security:

Earthquake, fire, equipment damage, power failure, theft

Device redundancy, line redundancy, data backup

2. Transport Security:

Stealing data on a transmission line

VPN encryption technology

3. Network interconnection Security:

Internet, in-system network, out-of-system network, internal LAN, Dial-Up Networking

Firewall, physical isolation, AAA authentication

4. System security:

Operating system vulnerabilities, vulnerabilities , misconfiguration

Vulnerability scanning, intrusion detection, virus protection

5. Application Security:

Application software, database , including resource sharing, Email, virus

Authentication, virus protection, data backup, disaster recovery

6. Managing Security:

Administrator rights, passwords, error actions, resource eggs, internal attacks, internal leaks

Authentication, access control, authorization

Multimedia:

1. Feel the media:

A person's senses can feel.

Sound, text, image, texture, smell, temperature, pressure ...

2. Indicate media:

A media constructed to process sensory media

Various digital coding (artificial media), various media files

3. Show the media:

A class of media that senses the conversion of media and communication signals. Include: input display media, output display media

I/O tools and devices, speakers, monitors

4. Storage media:

To store physical entities that represent media

Paper, record, videotape, tape, film, Memory

5. Transfer media:

A physical transfer medium that represents the transfer of media from one location to another

Communication cables, optical brazing, electromagnetic controls

Software

　　　　

　　

　　　　

　　

　　

　　

　　

2015 first half software designer Test Center, difficulty