The presence of multiple sub-arrays shortens the word and bit lines and this reduces the time to access the individual cells. The word lines control the gates of the transfer lines, while the bit bines are connected to the FET channel and are ultimately connected to the sense amplifiers.
One of the critical issues within the dynamic RAM is to ensure that the read and write functions are carried out effectively.
As voltages on the charge capacitors are small, noise immunity is a key issue. One of the problems with this arrangement is that the capacitors do not hold their charge indefinitely as there is some leakage across the capacitor. It would not be acceptable for the memory to lose its data, and to overcome this problem the data is refreshed periodically.
The data is sensed and written and this then ensures that any leakage is overcome, and the data is re-instated.
One of the key elements of DRAM memory is the fact that the data is refreshed periodically to overcome the fact that charge on the storage capacitor leaks away and the data would disappear after a short while. Typically manufacturers specify that each row should be refreshed every 64 ms.
There are a number of ways in which the refresh activity can be accomplished. Some processor systems refresh every row together once every 64 ms. Other systems refresh one row at a time, but this has the disadvantage that for large memories the refresh rate becomes very fast. Some other systems especially real time systems where speed is of the essence adopt an approach whereby a portion of the semiconductor memory at a time based on an external timer that governs the operation of the rest of the system.
In this way it does not interfere with the operation of the system. Whatever method is use, there is a necessity for a counter to be able to track the next row in the DRAM memory is to be refreshed. Some DRAM chips include a counter, otherwise it is necessary to include an additional counter for this purpose.
It may appear that the refresh circuitry required for DRAM memory would over complicate the overall memory circuit making it more expensive. However it is found that DRAM the additional circuitry is not a major concern if it can be integrated into the memory chip itself. As the size of memories increases, the issue of signal to noise ratio becomes very important.
At first sight, this may not appear to be a major issue, but it can give rise to issues of data corruption.
The signal to noise ratio depends upon the ratio of the capacitance of the storage capacitor within the DRAM memory to the capacitance of the Word or Bit line on which the charge is dumped when the cell is accessed. As the bit density per chip is increased, the ratio is degraded since the cell area is decreased as more cells are added on the bit line.
It is for this reason that it is important to store as high a voltage on the cell capacitor, and also to increase the capacitance of the DRAM storage capacitor for a given areas as much as possible.
These circuits perform functions such as:. Other functions of the memory controller include a series of tasks that include identifying the type, speed and amount of memory and checking for errors. Static RAM uses a completely different technology. A flip-flop for a memory cell takes four or six transistors along with some wiring, but never has to be refreshed. However, because it has more parts, a static memory cell takes up a lot more space on a chip than a dynamic memory cell.
Therefore, you get less memory per chip, and that increases its price. Memory chips in desktop computers originally used a pin configuration called dual inline package DIP.
This pin configuration could be soldered into holes on the computer's motherboard or plugged into a socket that was soldered on the motherboard. This method worked fine when computers typically operated on a couple of megabytes or less of RAM, but as the need for memory grew, the number of chips needing space on the motherboard increased. The solution was to place the memory chips, along with all of the support components, on a separate printed circuit board PCB that could then be plugged into a special connector memory bank on the motherboard.
Most of these chips use a small outline J-lead SOJ pin configuration, but quite a few manufacturers use the thin small outline package TSOP configuration as well. In other words, the pins are soldered directly to the surface of the board, not inserted in holes or sockets. Memory chips are normally only available as part of a card called a module. When you shop for memory, on many of the modules you can see the individual memory chips. The kinds of board and connector used for RAM in desktop computers have evolved over the past few years.
The first types were proprietary, meaning that different computer manufacturers developed memory boards that would only work with their specific systems. Then came SIMM , which stands for single in-line memory module. This memory board used a pin connector and was about 3. In most computers, you had to install SIMMs in pairs of equal capacity and speed.
This is because the width of the bus is more than a single SIMM. Each SIMM could send 8 bits of data at one time, while the system bus could handle 16 bits at a time. Later SIMM boards, slightly larger at 4. SIMM was used from the early s to early s. As processors grew in speed and bandwidth capability, the industry adopted a new standard in dual in-line memory module DIMM. DIMMs range in capacity and can be installed singly instead of in pairs. Capacity ranges from 2 to 32GB per module.
The industry has been moving to low-power DDR4 modules in thinner and lighter laptops, because they use less energy and are more compact. Unfortunately, they must be soldered into place, meaning the average user can't replace the original RAM. Most memory available today is highly reliable. Most systems simply have the memory controller check for errors at startup and rely on that.
Memory chips with built-in error-checking typically use a method known as parity to check for errors. Parity chips have an extra bit for every 8 bits of data.
The way parity works is simple. Let's look at even parity first. When the 8 bits in a byte receive data, the chip adds up the total number of 1s. If the total number of 1s is odd, the parity bit is set to 1. If the total is even, the parity bit is set to 0. When the data is read back out of the bits, the total is added up again and compared to the parity bit. If the total is odd and the parity bit is 1, then the data is assumed to be valid and is sent to the CPU.
But if the total is odd and the parity bit is 0, the chip knows that there is an error somewhere in the 8 bits and dumps the data. Odd parity works the same way, but the parity bit is set to 1 when the total number of 1s in the byte are even.
The problem with parity is that it discovers errors but does nothing to correct them. If a byte of data does not match its parity bit, then the data are discarded and the system tries again. Computers in critical positions need a higher level of fault tolerance. High-end servers often have a form of error-checking known as error-correction code ECC. Like parity, ECC uses additional bits to monitor the data in each byte.
The difference is that ECC uses several bits for error checking — how many depends on the width of the bus — instead of one. ECC memory uses a special algorithm not only to detect single-bit errors, but actually correct them as well.
ECC memory will also detect instances when more than one bit of data in a byte fails. Such failures are very rare, and they are not correctable, even with ECC. The majority of computers sold use nonparity memory chips.
These chips do not provide any type of built-in error checking, but instead rely on the memory controller for error detection. It's been said that you can never have enough money, and the same holds true for RAM, especially if you do a lot of graphics-intensive work or gaming. If your system responds slowly or accesses the hard drive constantly, then you need to add more RAM.
If you're upgrading to Windows 11, you'll need at least 4GB. Linux has a reputation for working happily on systems with low system requirements, including RAM. Xubuntu uses the lightweight Xfce desktop environment, which also works with other Linux distributions. Of course, there are distributions of Linux that have higher system requirements. You may also need more RAM if your computer acts as a server of some sort webpages, database, application, FTP or network. Another question is how much VRAM you want on your video card.
This is normally enough to operate in a typical office environment. You should probably invest in a higher-end graphics card if you want to do any of the following:. When shopping for video cards, remember that your monitor and computer must be capable of supporting the card you choose.
Most of the time, installing RAM is a very simple and straightforward procedure. The key is to do your research. Here's what you need to know:.
RAM is usually sold in densities with multiples of 2 gigabytes: 2, 4, 8, 16, In other words, the module is the same standard size, but there can be different amounts of memory on the same board. Once you know how much RAM you want, check to see what form factor card type you need to buy. You can find this in the manual that came with your computer or you can contact the manufacturer. It's important to realize that your options depend on the design of your computer.
High-end systems are moving to RIMM technology, which will eventually take over in standard desktop computers as well. Putting the wrong type of card in a slot can cause damage to your system and ruin the card. You will also need to know what type of RAM is required.
Some computers require very specific types of RAM to operate. Most computers are not quite that restrictive, but they do have limitations.
Additionally, some computers support dual-channel RAM configuration either as an option or as a requirement. When dual channel is an optional configuration, installing RAM in matched pairs speeds up the performance of certain applications.
Your computer is only configured to accept so much memory. There is a limited number of memory slots, and depending on your machine, you may be limited to an 8GB density module even if the manufacturer makes a 16 or 32GB module. Or, in some cases, your computer may allow you to upgrade the RAM that was installed in the factory. Some manufacturers — both computer and memory — offer a wizard on their websites where you can enter your computer's model to help you find what type of memory you'll need to install.
Check the system settings on your machine to find out how much memory is installed. Once you know how many slots there are and how much memory it can accept, you can decide how much memory to buy. Some manufacturers solder the base memory in place, but otherwise you may be able to uninstall a smaller RAM card and replace it with a larger one. Knowing your computer's configuration beforehand will help you avoid frustration when you buy memory.
Finding out you can't use what you bought after you've opened your computer up can be very, very annoying. Before you open your computer, check the end-user license agreement to make sure you won't be voiding the warranty in the process.
Some manufacturers seal the case and request that the customer have an authorized technician install RAM. If you're ready to open the case, turn off and unplug the computer. Ground yourself by using an anti-static pad or wrist strap to discharge any static electricity. Depending on your computer, you may need a screwdriver or nut-driver to open the case.
Some desktop systems come in tool-less cases that use thumbscrews or a simple latch. Laptops are often more challenging. The actual installation of the memory module does not normally require any tools.
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