What are the categories of memory? What are the different types of memory?

The performance indicators of memory include storage speed, storage capacity, CAS latency time, memory bandwidth, etc., which are described one by one below.

1. Storage speed.

The storage speed of memory is expressed in the time it takes to access data once, in nanoseconds, denoted as ns, 1 second = 1 billion nanoseconds, that is, 1 nanosecond = 10 9 seconds. The lower the ns, the shorter the access time, the faster the speed. At present, the access time of DDR memory is generally 6ns, and faster memory is mostly used on the video memory of the graphics card, such as:

5ns, 4ns, etc.

2. Storage capacity.

At present, the common memory storage capacity is 128MB, 256MB, 512MB, of course, there is also a single 1GB, memory, but its ** is higher, and ordinary users rarely use it. As far as the current ** point of view, use a single memory of more than 256MB at all times when configuring, and do not choose two 128MB solutions. Hint:

The formula for converting memory storage capacity is as follows: 1GB = 1024MB = 1024 x 1024KB

3. CL CL is the abbreviation of CAS lstency, that is, the CAS delay time, which refers to the reaction time of the longitudinal address pulse of the memory, and is one of the important markers to measure the memory of different specifications at a certain frequency. For the memory of PC1600 and PC2100, the specified CL should be 2, i.e. the delay time for him to read the data is two clock cycles. That is, he must operate steadily at his operating frequency with cl=2r.

4. SPD chip.

The SPD is an 8-pin, 256-byte EEROM (Erase-Writeable Programmable Read-Only Memory) chip. The location is generally on the right side of the front of the memory module, which records parameter information such as the speed, capacity, voltage, row and column addresses, and bandwidth of the memory. When the computer is turned on, the computer's BIOS will automatically read the information recorded in the SPD.

5. Parity.

Parity is when an extra bit is added to each byte of memory for error detection. When the CPU returns the data stored in the read, it will add the data stored in the first 8 bits again to determine whether the calculation result is consistent with the check. When the CPU finds that the two are different, it will automatically deal with them.

6. Memory bandwidth.

From the functional point of view of memory, we can think of memory as a bridge or warehouse between the memory controller (usually located in the northbridge chip) and the CPU. Obviously, the storage capacity of the memory determines the size of the "warehouse", and the band of the memory determines the "width and narrowness of the bridge", both of which are indispensable. Hint:

The memory bandwidth is determined as follows: b represents the bandwidth, f represents the memory clock frequency, and d represents the number of bits on the memory data bus, then the bandwidth b=f*d 8

For example, the bandwidth of a 100MHz SDRAM memory = 100MHz x 64 bit 8 = 800MB seconds.

The bandwidth of a common 133MHz SDRAM memory is 133MHz*64bit8=1064MB seconds.

There are three types of memory: DDR, DDR2, and DDR3.

The biggest difference between them is the frequency of work. The operating frequency directly affects the amount of data transferred by memory3.

For example: DDR2-800MHzIt has a memory bandwidth of:

800 * 64 bits 8=. That is, the amount of data it can transfer to the CPU in a second. ddr3-1333.

Its data transfer per second is: 1333 * 64 bits 8=.

1. Classified by storage medium.

Semiconductor memory: A memory composed of semiconductor devices.

Magnetic surface memory: A memory made of magnetic materials.

2. Classification according to storage mode.

RAM: The contents of any memory cell can be accessed randomly, regardless of the time of access and the physical location of the cell.

Sequential memory: It can only be accessed in a certain order, and the access time is related to the physical location of the storage cell.

3. Classified according to the read and write function of the memory.

Read-only memory (ROM): Semiconductor memory that is fixed and can only be read out but not written.

Random read-write memory (RAM): Semiconductor memory that can be read and written to as well as both.

4. Classification according to the storability of information.

Non-permanent memory: Memory that disappears when the power is off.

Permanent memory memory: A memory that can still hold information even after a power failure.

5. Classification according to the role in the computer system.

Main memory (memory): Used to store active programs and data, with high speed, small capacity, and high price per bit.

Secondary memory (external memory): It is mainly used to store programs and data that are currently inactive, and it is slow, large, and has a low price per bit.

Buffer memory: It mainly acts as a buffer for two parts with different working speeds.

Cache

RAM (random access memory), which is a memory module, is lost when the power is off.

ROM (Read-Only Memory), no data loss after power failure.

Memory is divided into six categories: basic memory, reserved memory, upper memory, high-end memory, expanded memory, and extended memory.

1. Basic memory.

It refers to the memory carried by the mobile phone itself, which is different from various external memory cards. For example, if a mobile phone has 60M memory, but it has a 1G memory card, then its basic memory is 60M. It is also used to refer to the amount of memory that comes with some brands of computers.

2. Reserve memory.

Generally, it occupies 640KB and 1024KB address space. Physical memory allocated to the display buffer memory, the ROM on each adapter card, and the system ROM BIOS, and the remaining space can be used as the upper memory for the physical memory taken from the physical expansion memory. This range of physical RAM can be used as shadow RAM.

3. Upper memory.

It is the memory of the first layer above the regular memory, also known as the DOS high-end memory (the address is 0a0000h 0fffffh). Created using unallocated address space in reserved memory, its physical memory is acquired by physical extended memory.

4. High-end memory.

The first 64kb area in extended memory (1024kb 1088kb) Established and managed.

5. Expand memory.

It was an early standard for increasing memory, up to 32 MB. To use the expanded memory, you must install a special expansion memory board on your computer, and you must also install a hypervisor to manage the expansion memory board.

6. Expand memory.

In the microcomputer above 386, there are two memory working modes, one is called the real address mode or the real mode, and the other is called the protection mode. In the real mode, the physical address still uses 20 bits, so the maximum addressing space is 1MB for compatibility with 8086. The protection method uses a 32-bit physical address with an addressing range of up to 4GB.

According to the working principle of memory, it can be divided into three categories: read-only memory, random memory, and cache memory.

1. Read-only memory.

At the time of manufacture, information (data or programs) is stored and stored permanently. This information can only be read out, generally not written, and this data will not be lost even if the machine has a power outage.

2. Random access.

RAM means that data can be read or written from it. When the power of the machine is turned off, the data stored in it is lost.

3. High-speed buffer memory.

When the CPU writes or reads data to memory, that data is stored in cache memory.