(turn) Register, RAM, ROM, Flash related concepts difference collation

Transfer from http://m.blog.chinaunix.net/uid-30077524-id-5570244.html

The article speaks very clearly about these things and is worth collecting.

Register

Registers are the constituent parts of the central processing Unit. It's about 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).

Memory

The memory range is the largest and it covers almost all areas of storage. What you call registers, memory, is a kind of memory inside. Any hardware that has storage capacity can be called memory, it is natural, hard disk more obvious, it into the ranks of the external memory, it is thus ——。

Memory

Memory is the professional name of the internal memory, it is not a mysterious thing, it is only the memory of the bucket, it covers the scope is also very large, generally divided into read-only memory and then memory, and the most powerful buffer memory (cache), read-only memory is widely used, It is usually a piece of hardware integrated on the readable chip, the role is to identify and control the hardware, it is characterized by only readable, can not be written. The characteristic of random memory is readable and writable, all data disappears after power off, we refer to the memory bar refers to it.

CACHE

The cache is a very small amount of memory in the CPU, which is the most powerful memory in the computer memory. Because of the technical constraints, capacity is difficult to improve, generally not trillion.

The difference between ROM and RAM:

ROM (read-only memory or cured memory)

RAM (Random access memory)

Rom and Ram refer to the semiconductor memory, ROM is the abbreviation of Read only memory, RAM is the abbreviation of random Access memory. Rom can still hold data while the system is powered off, and ram usually loses data after power-down, typical RAM is the memory of the computer.

There are two main types of RAM, called Static RAM (Ram/sram), that do not disappear when data is stored in it. SRAM is very fast and is the fastest storage device to read and write at the moment. When the SRAM unit is given a state of 0 or 1, it will remain in this state until the next time it is given a new state or a power outage before it changes or disappears. But storing 1bit of information requires 4-6 transistors. So it's also very expensive, so it's only used in demanding places, such as CPU buffers, level two buffers. The other is called Dynamic RAM (Ram/dram), and DRAM must be refreshed in a certain amount of time to keep the data stored in it. DRAM can be achieved with only 1 transistors. DRAM retains data for a short period of time, slower than SRAM, but it is faster than any ROM, but from the price of DRAM is much cheaper than SRAM, computer memory is DRAM.

There are many types of dram, common mainly fpram/fastpage, Edoram, SDRAM, DDR RAM, RDRAM, Sgram, and Wram, which are described in one of the DDR RAM. DDR RAM (Date-rate RAM) is also known as DDR SDRAM, which is basically the same as the improved RAM and SDRAM, except that it can read and write two of times on a single clock, thus doubling the data transfer speed. This is the most used memory in the current computer, and it has a cost advantage, in fact defeating Intel's other memory standard-rambus DRAM. On many high-end graphics cards, high-speed DDR RAM is also available to increase bandwidth, which significantly improves the pixel rendering capabilities of 3D accelerator cards.

There are many types of ROM, the prom is a programmable rom,prom and EPROM (erasable programmable ROM) The difference is that the prom is a one-time, that is, after the software is poured, it can not be modified, this is an early product, it is now impossible to use, The EPROM is a kind of universal memory by wiping out the original program by ultraviolet light irradiation. Another type of EEPROM is the electronic wipe, the price is very high, the write time is very long, writing is very slow.

Initially, the read-only memory is called ROM (read Only memory), and the data is not lost after power-down. It is inconvenient to use because it cannot be rewritten. With the advancement of technology, the use of some new technologies in ROM makes it possible to have programmable functions. The earlier is the fuse type of programmable ROM, because it is programmed by fusing fuse, so this type of ROM programming, it can not be written again, is a one-time (OTP). Later, there was an EPROM, which was erased by ultraviolet light, and programmed by high pressure, which generally had a transparent quartz glass window, which looked pretty, and it was used for ultraviolet radiation. Later, the EEPROM, without ultraviolet radiation can be erased, so you can directly in the circuit programming. There are also flash ROM, also can be divided into nor flash and NAND flash. FLASH ROM generally has a feature, that is, when writing data, you can change 1 to 0, and not 0 to 1, so write data before you need to erase, erase all data set 1.

The reason is still called Rom, summed up, probably for several reasons:

① cannot be written as fast as RAM;

② may require a special write-off voltage;

③ may require special write-off timing;

④ may need to be erased before writing;

⑤ write a limited number of times, not like Ram can be freely written without damage;

⑥ data is not lost after power-down;

⑦ Some writable memory can only be written once (OTP).

For example, mobile phone software is generally placed in the EEPROM, we call, some of the last dialed number, is currently in the SRAM, not immediately write through the record (call record saved in the EEPROM), because there is very important work (call) to do, if written, The long wait is unbearable to the user.

Flash memory, also known as Flash, combines the advantages of ROM and RAM, not only with electronic erasable programmable (EEPROM) performance, but also without power loss data can be quickly read data (NVRAM advantage), u disk and MP3 used in this kind of memory. In the past 20 years, embedded systems have been using ROM (EPROM) as their storage devices, but in recent years Flash has replaced the ROM (EPROM) in the embedded system, Used as storage bootloader as well as operating system or program code or directly on the hard disk (USB drive).

There are two main flash and Flash and NADN Flash. Nor Flash read the same as our common SDRAM read, the user can directly run the code loaded in nor flash, which can reduce the capacity of SRAM and thus save costs. NAND Flash does not take the memory of random read technology, its reading is in a single read a fast form, usually read 512 bytes at a time, the use of this technology flash relatively inexpensive. The user cannot directly run the code on NAND flash, so a lot of the development boards using NAND flash use a small nor flash to run the startup code in addition to the NAND Flah.

Generally small-capacity with nor Flash, because of its fast reading speed, much to store the operating system and other important information, while the large capacity of NAND flash, the most common NAND flash applications are embedded system using the doc (disk on Chip) and our usual "flash disk", can be erased online. The current flash on the market mainly comes from Intel,amd,fujitsu and Toshiba, while the main manufacturers of NAND Flash are Samsung and Toshiba.

NOR Flash and NAND flash comparison

NOR Flash manufacturer has Intel and St, Nand Flash manufacturers have Hynix,micon,samsung,toshiba and Fujitsu and so on.

2006 NAND will occupy 59% of the flash market share, nor's market share will fall to 41%. By 2009, the market share of NAND will rise to 65%,nor's market share will fall further to 35%.

NAND main applications: Compacflash,secure digi-tal,smartmedia,sd,mmc,xd,pc CARD,USB sticks, etc.

Nor's transmission efficiency is very high, in small capacity with a high cost-effective, more secure, not prone to data failure, therefore, the main application to code storage-based, and more related to the operation.

Currently, NAND Flash is used primarily in digital camera flash cards and MP3 players, both of which are growing very quickly. and NOR chips are mainly used in mobile phones and set-top boxes, these two markets are relatively slow growth.

Performance comparison

Flash Flash memory is non-volatile memory, can be called Block of memory unit block for Erasure and re-programming. The write operation of any flash device can only be done within an empty or erased unit, so in most cases the erase must be performed before the write operation. The erasure of NAND devices is straightforward, and nor does it require that all bits in the target block be written to 0 before erasing.

Since the erase nor device is carried out in a 64~128kb block, the time to perform a write/erase operation is 5s, in contrast, the erasure of the NAND device is carried out in a 8~32kb block, and the same operation is performed for up to 4ms.

The difference in block size when performing the erase further widens the performance gap between nor and NADN, and statistics show that for a given set of writes (especially when updating a small file, more erase operations must be done in the nor-based unit. This way, when choosing a storage solution, the designer must weigh the following factors.

Nor reads faster than NAND.

Nand writes much faster than nor.

NAND's 4ms erase speed is much faster than nor 5s.

Most write operations require a wipe operation first.

The NAND erase unit is smaller and the corresponding erase circuit is less.

Interface differences

NOR Flash has an SRAM interface with enough address pins to be addressable, which makes it easy to access every byte inside of it.

NAND devices use complex I/O ports to sequentially access data, and the methods of each product or vendor may vary. 8 pins are used to transmit control, address, and data information.

NAND read and write operations take a 512-byte block, which is a bit like a hard drive to manage such operations, and it is natural that NAND-based storage can replace hard disks or other block devices.

Capacity and cost

NAND Flash unit sizes are almost half the size of NOR devices, and because of the simpler production process, NAND structures can provide higher capacity within a given mold size and correspondingly lower prices.

Nor Flash occupies the bulk of the 1~16MB flash market, while NAND flash is used only in 8~128MB products, which also shows that nor is it primarily used in code storage media, NAND is suitable for data storage, NAND in CompactFlash, The largest share of Secure Digital, PC cards and MMC memory cards is in the market.

Reliability and durability

One of the key issues to consider when using flahs media is reliability. Flash is a very suitable storage solution for systems that require extended MTBF.

The reliability of nor and NAND can be compared from three aspects of longevity (durability), bit switching and bad block handling.

Longevity (durability)

The maximum number of erase times per block in the NAND flash memory is 1 million, and nor is 100,000 times the number of erase writes. In addition to the 10:1 block erase cycle advantage of NAND memory, the typical NAND block size is 8 times times smaller than nor, and each NAND memory block is removed less frequently within a given time.

-bit switching

All flash devices are subject to the phenomenon of bit switching. In some cases (rarely seen, NAND occurs more often than nor), a bit is reversed or reversed.

One change may not be obvious, but if it happens on a critical file, this small glitch can lead to system downtime. If you just report a problem, read it a few times and it can be solved.

Of course, if this bit really changes, then the error detection/error correction (EDC/ECC) algorithm must be used. Bit reversal issues are more common in NAND flash, NAND vendors recommend using NAND flash while using the EDC/ECC algorithm.

This problem is not fatal when storing multimedia information in NAND. Of course, if you are using a local storage device to store operating systems, configuration files, or other sensitive information, you must use the EDC/ECC system to ensure reliability.

Bad block handling

The bad blocks in the NAND device are randomly distributed. There have been efforts to eliminate the bad block, but found that the yield is too low, the price is too high, it is not cost-effective.

The NAND device requires an initial scan of the media to discover the bad block and mark the bad block as unavailable. In a device that has been made, if a reliable side

This treatment will result in a high failure rate.

Easy to use

You can use nor-based flash memory very directly, you can connect like other storage, and you can run code directly on it.

NAND is much more complex due to the need for I/O interfaces. Access methods for various NAND devices vary by manufacturer.

When using a NAND device, you must write to the driver before you can continue with other operations. Writing information to NAND devices requires considerable skill, as

Designers should never write to bad blocks, which means that virtual mappings must be performed throughout the NAND device.

Software support

When discussing software support, you should distinguish between basic read/write/erase operations and high-level software for disk emulation and flash management algorithms, including performance optimizations.

No software support is required to run code on nor devices, and in the same operation on NAND devices, drivers are often required, i.e. memory technology drivers (MTD), and NAND and nor devices require MTD for both write and erase operations.

There is a relatively small amount of MTD required to use nor devices, and many vendors offer more advanced software for nor devices, including the M-system TrueFFS driver, which is driven by Wind River System, Microsoft, QNX software Sy Used by manufacturers such as STEM, Symbian, and Intel. The drive is also used to simulate and manage NAND flash for diskonchip products, including error correction, bad block handling, and loss balancing.

The difference between ROM and hard disk (computer hard disk is not rom,bios in ROM):

Read-only memory is a ROM, which is a separate internal memory, similar to random RAM (that is, memory), but can only be read to store and save permanent data. Read-only ROM data cannot be updated at random, but can be read at any time. ROM can retain data even when power is lost.

Injecting data into the ROM requires an additional compiler, which does not have this function on the PC. Generally in the ROM before the factory to inject information, no special circumstances generally do not change the content, that is, usually a lifetime is the same content.

The one thing that's easy to misunderstand in PC is that people often confuse ROM with harddisk (hard disk), harddisk is external memory, and ROM is internal memory. The look is also very different, hard disk is a cubic thing, and rom more like a flat fixed strip of things. The hard drive can easily rewrite the content, but the ROM is not available. And the capacity of the hard disk is much larger than the ROM.

In the PC ROM content has the BIOS program and the machine code and the factory information and so on things.

And the external memory of the computer using a similar tape-like device is called a disk. Floppy disk, hard disk, USB stick, etc. are all disks.

(turn) Register, RAM, ROM, Flash related concepts difference collation