Computer System: Chapter 2 (storage hierarchy)

References: A thorough understanding of computer systems, Chapter 6

6.1.1 Random Access to Memory RAM

1. Static RAM (SRAM) and dynamic RAM (DRAM)

First. Basic concept: the structure of a single bit in the SRAM storage requires six transistors, and the structure of a single bit in the DRAM storage is a capacitor (DRAM can reach a higher density than the SRAM ). As a result, SRAM is more expensive than DRAM, resulting in faster access. (A desktop system has a maximum of several megabytes of SRAM, and DRAM can contain hundreds to thousands of bytes)

Then. The concept of an advanced point. SRAM is in a stable state, and DRAM (capacitor) is prone to leakage in many cases, so that DRAM needs to refresh each bit through "re-reading and re-writing" every cycle time. (Some DRAM uses error codes such as 38 BITs to encode 32 bits to solve this problem)

Last. SRAM is used as a high-speed cache. It can be on-chip or off-chip (it can be sitting on a chip with the CPU or separated from chip ); DRAM is used as the frame buffer for main memory and graphics systems (it is estimated that it is a "video card ").

2. What is the image of traditional DRAM?

W DRAM units (one unit stores one bit) to form a supercell (if the DRAM chip is a matrix, then a supercell is a matrix element) ---"

D supercells form a * B matrix to form a DRAM chip, in this way, the chip has a * B * w bits (the reason why d supercells form a matrix instead of a linear array is to reduce the number of address pins on the chip. However, the disadvantage of matrix organization is to take two steps to send the address: Row + column, which increases the access time) ---"

Multiple DRAM chips are packed in the memory module, which is the expansion slot of the diesel cutter motherboard. ---"

Chip inflows and outflows through external connectors called pin

3. How to access primary storage

First. Who in the computer needs to access the primary storage? Is the CPU. The main memory exists outside the CPU (off the chip)

Next, let's talk about the process of accessing the primary memory: Data Streams pass back and forth between the CPU and DRAM through a shared electronic circuit that becomes a bus.

For more information, see.

1) different computer systems have different designs for the bus. This book uses one of the advanced bus architecture. The specific structure is shown in Figure 6-6. therefore, how the CPU accesses the main memory is based on this bus architecture.

2) data flows between chips (CPU--I/O bridge-main memory) through the bus (which includes the system bus and memory bus.