Information Security System Design Foundation Sixth Week study summary

Learning Goals:

1. Understanding common Storage technologies (RAM, ROM, disk, SSD, etc.)

2. Understanding the principle of locality

3. Understanding Caching Ideas

4. Understanding the principle of locality and the application of caching ideas in the storage hierarchy

5. Principle and application of cache

Learning tasks:

1. Read the textbook and complete the After-school practice (the book has a reference answer)

Focus: 6.2 6.3 6.4 6.8 6.9 6.10 6.11 6.12 6.13

2. Examination: Exercises to change the data

3. Experiment: Need to practice in the lab building

Memory hierarchy

6.1 Storage Technology

Random access Memory (RAM):

• It is divided into static (SRAM) and dynamic (DRAM). Static is faster and more expensive than dynamic. SRAM is used to make cache memory. DRAM is used as a frame buffer for primary and graphical systems.

• SRAM stores each bit in a bistable memory unit. This circuit can be maintained indefinitely in one of two different voltage configurations or states. As long as there is electricity, it will keep its value forever. Even if there is interference, the circuit will return to a stable value when the interference is eliminated.

• DRAM stores each bit as a charge to a capacitor. Very sensitive to interference. The DRAM loses its charge in 10~100 milliseconds, and the computer's clock cycle is measured in nanoseconds, and the memory system periodically reads through it and rewrites it to flush every bit of memory.

• In the traditional dram:dram, the cell stores information by row and column. The storage controller sends a send-off address, a column address, and reads the contents of the superclass via two pins. The DRAM chip has an internal line buffer, receives the line address, copies a line of content to the buffer, and reads the contents of the specified superclass at the column address.

• Enhanced DRAM: Fast-page mode dram, extended data output dram, synchronous dram, double data rate synchronous DRAM, Rambus dram, video dram.

• Non-volatile Memory: ROM, the information is not lost after power failure. Prom can only be programmed once. Erasable writable programming ROM (EPROM), electronic erasable ROM (EEPROM). Flash-based EEPROM provides non-volatile storage for a large number of electronic devices. A solid-state drive is a flash-based disk drive.

• Access to main memory: data transfer between CPU and main memory is done via bus transaction. A bus-type set of parallel conductors that can carry addresses, data, and control signals. The I/O bridge translates the electronic signal of the system bus into the electronic signal of the memory bus. The contents of address A are loaded into register%eax, and the contents of register%eax are written to address a, respectively, read transaction, write transaction

• The disks are made of platters and are covered with magnetic recording materials. The disk consists of one or more stacked platters, sealed and packaged.

• Disk capacity: Record density, track density, surface density.

• Disk operation: Seek time, the time required to move the transmission arm, usually 3~9ms, the rotation time, after positioning to the desired track, the drive waits for the first bit of the target sector to rotate to the read-write header, transfer time, the drive begins to read or write the contents of the sector.

• Connect to I/O Devices: Universal Serial Bus (USB), graphics card, Host bus adapter

• To access the disk:

• SSD: The SSD packet is plugged into the I/O bus. An SSD package consists of one or more flash chips and a flash translation layer, instead of a mechanical drive in a traditional rotating disk. SSDs consist of semiconductor memory with no moving parts, so the random access time is faster than rotating the disk, consumes less energy, and is more robust. But easy to wear.

• Different storage technologies have different price and performance tradeoffs.

6.2 Local Sex

• Locality: The locality of a computer, meaning that they tend to refer to data items that are adjacent to other recently referenced data items, or to the data item itself that has recently been referenced. Temporal locality and spatial locality. The various levels of modern computer systems take advantage of locality.

6.3 Memory Hierarchy

• Caching: For each k, a faster and smaller storage device located on the K-tier is cached as a larger and slower storage device at the k+1 layer.

• Cache hit, when a program needs a data object D in Layer k+1, it first looks for D in a block that is currently stored in the K layer. If D is just cached in level K, that's the cache hit.

• Cache misses: As above, if there is no cache data Object K in layer K, that is the cache miss. Category: Mandatory misses/cold misses, conflict misses, capacity misses.

6.4 Cache Memory

Information Security System Design Foundation Sixth Week study summary