Important test big issue
A classification memory
The memory is a computer system memory devices, for storing programs and data, from a different perspective on the memory can do different classification.
1, a storage medium divided by
- The semiconductor memory (also known as a volatile memory): Small size, low power consumption, short access time, when the power goes off, the stored information will disappear.
- Magnetic surface of the memory (nonvolatile memory): The disk
- An optical disc memory (nonvolatile memory): robust, reliable, optical disk
2, by way of access points
- Random access memory (RAM): Any memory content can be accessed at random like the array index, the elements can be accessed directly. Access speed, commonly used in the production of main memory and Cache
- Sequential access memory (SAM): Only some order to access, i.e., access time and related to the physical location of the access unit. (Such as tape)
- Direct access storage device (DAM): The disk
- Associative memory (CAM): by content retrieval
3, action points by the computer
Second, the hierarchy of the computer
There are three memory performance, speed, capacity, cost per bit (bit value).
General rule, the higher the speed, the higher the bit value, the smaller the capacity. Conversely, the lower the speed, the lower the bit value, the greater the capacity.
Hierarchical storage system is mainly reflected in the cache - the two cache storage hierarchy - main memory and main memory. Figure:
- Cache - main memory hierarchy : The main problem at this level CPU and main memory speed mismatch, the main memory used to store will be involved in running programs and data. However, a big difference with the CPU speed, in order to make a better match velocity between them, then insert a faster than main memory, a smaller capacity high-speed memory (Cache) between the main memory and the CPU, so long as to use the information recently transferred to the cache, CPU will be able to get information directly from the cache. Note that the main memory is done automatically by the hardware and the data cache mobilization, transparent to the programmer.
- Main memory - secondary storage level : this level of the storage system to solve the capacity problem, lower secondary memory speed, but large capacity for storing information temporarily unused, when the CPU to use this information, the auxiliary storage contents transferred to the main memory for the CPU to directly access the data between the main memory and the mobilization of secondary memory is hardware and operating system together to complete.
Third, the semiconductor memory chip random
The semiconductor memory chip has a random memory matrix memory function, the decoder driver circuit and a read / write circuit and the like.
Write circuit: includes a sense amplifier and write circuit, used to complete the read / write operation.
Address lines: an input-capacity relating to the number of bits to chip
the chip select lines: determine which chip is selected (used to chip select)
data lines: bidirectional input, the number of bits read or written to the chip of the digit related, but also with chip capacity.
storage capacity
We storage capacity typically expressed as:
number of words X bits, such as bits 64K X8, its meaning is 8 bits constituting one word, a total of 64 words. This concept should be very familiar with, behind understanding the question useful.
Let's look at an example:
A 64K x 8-bit memory may be constituted by () th bit memory chip 16k x1?
Analysis: 64K x 8-bit, indicating that the memory is 8 constitute a word, therefore, every word is read out, it is necessary to select 16k x1 8-bit memory chips, and can represent a 16K, and therefore needs a total 64/16 = 4, according to the principle of combination, need a total of 4x8 = 32 slices.
We can see from the figure, corresponding to the chips 32 divided into four groups of eight (8 represented).
So we conclude that:
The semiconductor random access, multi-called RAM is customary to store information according to the different principles, it can be divided into static RAM (SRAM) and dynamic RAM (DRAM)