Memory management in windows 2000-pdf

A bit later, Toshiba was successful with an IBM laptop clone. Since these early models, many manufacturers have introduced and improved laptop computers over the years. Today's laptops are much more sophisticated, lighter and closer to Kay's original vision. The First Laptop? The sale catalog describes it as a "K byte bubble memory lap-top computer with diecast magnesium case and folding electroluminescent graphics display screen.

When you think about it, it's amazing how many different types of electronic memory you encounter in daily life. What you may not know is that most of the electronic items you use every day have some form of memory also. In this article, you'll learn why there are so many different types of memory and what all of the terms mean. RAM Basics Similar to a microprocessor, a memory chip is an integrated circuit IC made of millions of transistors and capacitors. In the most common form of computer memory, dynamic random access memory DRAM , a transistor and a capacitor are paired to create a memory cell , which represents a single bit of data.

The capacitor holds the bit of information -- a 0 or a 1. The transistor acts as a switch that lets the control circuitry on the memory chip read the capacitor or change its state. A capacitor is like a small bucket that is able to store electrons. To store a 1 in the memory cell, the bucket is filled with electrons.

To store a 0, it is emptied. The problem with the capacitor's bucket is that it has a leak. In a matter of a few milliseconds a full bucket becomes empty. Therefore, for dynamic memory to work, either the CPU or the memory controller has to come along and recharge all of the capacitors holding a 1 before they discharge.

To do this, the memory controller reads the memory and then writes it right back. This refresh operation happens automatically thousands of times per second. The capacitor in a dynamic RAM memory cell is like a leaky bucket. It needs to be refreshed periodically or it will discharge to 0. This refresh operation is where dynamic RAM gets its name. Dynamic RAM has to be dynamically refreshed all of the time or it forgets what it is holding.

The downside of all of this refreshing is that it takes time and slows down the memory. Memory cells are etched onto a silicon wafer in an array of columns bitlines and rows wordlines.

The intersection of a bitline and wordline constitutes the address of the memory cell. Memory is made up of bits arranged in a two-dimensional grid. In this figure, red cells represent 1s and white cells represent 0s. In the animation, a column is selected and then rows are charged to write data into the specific column. DRAM works by sending a charge through the appropriate column CAS to activate the transistor at each bit in the column.

When writing, the row lines contain the state the capacitor should take on. When reading, the sense-amplifier determines the level of charge in the capacitor.

If it is more than 50 percent, it reads it as a 1; otherwise it reads it as a 0. The counter tracks the refresh sequence based on which rows have been accessed in what order. The length of time necessary to do all this is so short that it is expressed in nanoseconds billionths of a second. A memory chip rating of 70ns means that it takes 70 nanoseconds to completely read and recharge each cell.

Memory cells alone would be worthless without some way to get information in and out of them. So the memory cells have a whole support infrastructure of other specialized circuits.

Static RAM uses a completely different technology. In static RAM, a form of flip-flop holds each bit of memory. 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 makes static RAM a lot more expensive.

How Much Do You Need? 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. At 64MB, you may experience frequent application problems.

For optimal performance with standard desktop applications, MB is recommended. If you plan to add X-Windows or do much serious work, however, you'll probably want 64 MB. You may also need more RAM if your computer acts as a server of some sort. Another question is how much VRAM you want on your video card. This is normally enough to operate in a typical office environment. Read-only memory ROM , also known as firmware , is an integrated circuit programmed with specific data when it is manufactured.

ROM chips are used not only in computers, but in most other electronic items as well. In this edition you will learn about the different types of ROM and how each works.

This means that removing the power source from the chip will not cause it to lose any data. While RAM uses transistors to turn on or off access to a capacitor at each intersection, ROM uses a diode to connect the lines if the value is 1.

If the value is 0, then the lines are not connected at all. Figure 1. A diode normally allows current to flow in only one direction and has a certain threshold, known as the forward breakover , that determines how much current is required before the diode will pass it on.

In silicon-based items such as processors and memory chips, the forward breakover voltage is approximately 0. By taking advantage of the unique properties of a diode, a ROM chip can send a charge that is above the forward break over down the appropriate column with the selected row grounded to connect at a specific cell.

If a diode is present at that cell, the charge will be conducted through to the ground, and, under the binary system, the cell will be read as being "on" a value of 1. The neat part of ROM is that if the cell's value is 0, there is no diode at that intersection to connect the column and row. So the charge on the column does not get transferred to the row. As you can see, the way a ROM chip works necessitates the programming of perfect and complete data when the chip is created.

You cannot reprogram or rewrite a standard ROM chip. If it is incorrect, or the data needs to be updated, you have to throw it away and start over. Creating the original template for a ROM chip is often a laborious process full of trial and error. But the benefits of ROM chips outweigh the drawbacks. Once the template is completed, the actual chips can cost as little as a few cents each. They use very little power, are extremely reliable and, in the case of most small electronic devices, contain all the necessary programming to control the device.

A great example is the small chip in the singing fish toy. This chip, about the size of your fingernail, contains the second song clips in ROM and the control codes to synchronize the motors to the music. Blank PROM chips can be bought inexpensively and coded by anyone with a special tool called a programmer. The difference is that every intersection of a column and row in a PROM chip has a fuse connecting them. A charge sent through a column will pass through the fuse in a cell to a grounded row indicating a value of 1.

Since all the cells have a fuse, the initial blank state of a PROM chip is all 1s. To change the value of a cell to 0, you use a programmer to send a specific amount of current to the cell. The higher voltage breaks the connection between the column and row by burning out the fuse. This process is known as burning the PROM. Figure 2 PROMs can only be programmed once. They are more fragile than ROMs. A jolt of static electricity can easily cause fuses in the PROM to burn out, changing essential bits from 1 to 0.

Even though they are inexpensive per chip, the cost can add up over time. EPROM chips can be rewritten many times. Once again we have a grid of columns and rows. The two transistors are separated from each other by a thin oxide layer.

One of the transistors is known as the floating gate and the other as the control gate. The floating gate's only link to the row wordline is through the control gate.

As long as this link is in place, the cell has a value of 1. To change the value to 0 requires a curious process called Fowler-Nordheim tunneling. Tunneling is used to alter the placement of electrons in the floating gate. An electrical charge, usually 10 to 13 volts, is applied to the floating gate. The charge comes from the column bitline , enters the floating gate and drains to a ground. This charge causes the floating-gate transistor to act like an electron gun.

The excited electrons are pushed through and trapped on the other side of the thin oxide layer, giving it a negative charge. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing.

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Another way to explain is if we launch an application e. When a process requests a page, it brings the oldest page first. Those pages are not overwritten, because they only represent a copy of data that was once being used by this process. So windows keep those on several paging list. The way that the windows memory manager keeps track of this is that it keeps track of this unassigned memory in one of four paging lists.

Memory manager may need to choose this location or list while performing a page reading. When it gets that size, a zero page thread also known as kernel thread is awakened that runs in priority 0. Besides, windows may need zeroed page. But that page may still needed by the process, moreover it may have to be reused by the process. It may being on the standby or modified page list represents code or a DLL of an image and be reused by another process [2].

Discussion and Conclusion Proper management of memory is vital for every computer operating system. Modern advance operating system e. Skip to main content. Windows Performance Guide by. Start your free trial. Chapter 6.