COMSATS Institute of Information Technology, Islamabad

COMPUTING FOR MANAGEMENTFinal project report

PROJECT : Random Access Memory

SUBMITTED TO: Sir Azfar Shakeel

PRESENTED BY:

NAME: REG NO:

Muhammad Mubashir CIIT/FA09-MBA-101/ISB

Muhammad Muneeb CIIT/FA09-MBA-102/ISB

Muhammad Tariq Maqbool CIIT/FA09-MBA-112/ISB

Waseem Akhter CIIT/FA09-MBA-189/ISB

Farhan Ahmad CIIT/FA09-MBA-122/ISB

CLASS: MBA 1st (Section B)

1

RANDOM ACCESS MEMORY

INTRODUCTION:Random-access memory is a form of computer data storage. Today, it takes the form of integrated circuits that allow stored data to be accessed in any order. RAM stands for Random Access Memory. It is also called main memory or Direct Access Memory. Random access means that each individual byte in the entire memory is directly accessible. A program must be loaded into RAM before execution. RAM is temporary memory. When the power is turned off, the information in this memory is lost. Thus it is called volatile memory. CPU can read data from RAM and write data to RAM. That is why RAM is also known as read/write memory. It is used to store data and instruction while it is being executed.

HISTORY:

An early type of widespread writable random-access memory was the magnetic core memory, developed from 1949 to 1952, and subsequently used in most computers up until the development of the static and dynamic integrated RAM circuits in the late 1960s and early 1970s. Before this, computers used relays, delay line memory, or various kinds of vacuum tube arrangements to implement "main" memory functions. some of which were random access, some not. Latches built out of vacuum tube triodes, and later, out of discrete transistors, were used for smaller and faster memories such as random-access register banks and registers. Prior to the development of integrated ROM circuits, permanent (or read-only) random-access memory was often constructed using semiconductor diode matrices driven by address decoders.

2

WHY RANDOM ACCESS?RAM is called "random access" because any storage location can be accessed directly. Originally, the term distinguished regular core memory from offline memory, usually on magnetic tape in which an item of data could only be accessed by starting from the beginning of the tape and finding an address sequentially. Perhaps it should have been called "nonsequential memory" because RAM access is hardly random. RAM is organized and controlled in a way that enables data to be stored and retrieved directly to specific locations. Note that other forms of storage such as the hard disk and CD-ROM are also accessed directly (or "randomly") but the term random access is not applied to these forms of storage. In addition to disk, floppy disk, and CD-ROM storage, another important form of storage is read-only memory (ROM), a more expensive kind of memory that retains data even when the computer is turned off. Every computer comes with a small amount of ROM that holds just enough programming so that the operating system can be loaded into RAM each time the computer is turned on.

RAM VS HARD DISK

RAM can be compared to a person's short-term memory and the hard disk to the long-term memory. The short-term memory focuses on work at hand, but can only keep so many facts in view at one time. If short-term memory fills up, your brain sometimes is able to refresh it from facts stored in long-term memory. A computer also works this way. If RAM fills up, the processor needs to continually go to the hard disk to overlay old data in RAM with new, slowing down the computer's operation. Unlike the hard disk which can become completely full of data so that it won't accept any more, RAM never runs out of memory. It keeps operating, but much more slowly than you may want it to.

HOW BIG IS RAM?RAM is small, both in physical size (it's stored in microchips) and in the amount of data it can hold. It's much smaller than your hard disk. A typical computer may come with 256 million bytes of RAM and a hard disk that can hold 40 billion bytes. RAM comes in the form of "discrete" (meaning separate) microchips and also in the form of modules that plug into holes in the computer's motherboard. These holes connect through a bus or set of electrical paths to the processor. The hard drive, on the other hand, stores data on a magnetized surface that looks like a phonograph record.

Most personal computers are designed to allow you to add additional RAM modules up to a certain limit. Having more RAM in your computer reduces the number of

3

times that the computer processor has to read data in from your hard disk, an operation that takes much longer than reading data from RAM. (RAM access time is in nanoseconds; hard disk access time is in milliseconds.)

WHAT RAM LOOKS LIKE:In general, RAM is much like an arrangement of post-office boxes in which each box can hold a 0 or a 1. Each box has a unique address that can be found by counting across columns and then counting down by row. In RAM, this set of post-office boxes is known as an array and each box is a cell. To find the contents of a box (cell), the RAM controller sends the column/row address down a very thin electrical line etched into the chip. There is an address line for each row and each column in the set of boxes. If data is being read, the bits that are read flow back on a separate data line. In describing a RAM chip or module, a notation such as 256Kx16 means 256 thousand columns of cells standing 16 rows deep.

In the most common form of RAM, dynamic RAM, each cell has a charge or lack of charge held in something similar to an electrical capacitor. A transistor acts as a gate in determining whether the value in the capacitor can be read or written. In static RAM, instead of a capacitor-held charge, the transistor itself is a positional flip/flop switch, with one position meaning 1 and the other position meaning 0.

Externally, RAM is a chip that comes embedded in a personal computer motherboard with a variable amount of additional modules plugged into motherboard sockets. To add memory to your computer, you simply add more RAM modules in a prescribed configuration. These are single in-line memory modules (SIMMs) or dual in-line memory modules (DIMMs). Since DIMMs have a 64-bit pin connection, they can replace two 36-bit (32-bits plus 4 parity bits) SIMMs when synchronous DRAM is used. Laptop and notebook computers contain smaller 32-bit DIMMs known as small outline DIMMs (SO DIMMs).

HOW DATA IS ACCESSED:When the processor or CPU gets the next instruction it is to perform, the instruction may contain the address of some memory or RAM location from which data is to be read (brought to the processor for further processing). This address is sent to the RAM controller. The RAM controller organizes the request and sends it down the appropriate address lines so that transistors along the lines open up the cells so that each capacitor value can be read. A capacitor with a charge over a certain voltage level represents the binary value of 1 and a capacitor with less than that charge represents a 0. For dynamic RAM, before a capacitor is read, it must be power-refreshed to ensure that the value read is valid. Depending on the type of RAM, the entire line of data may be read that the specific address happens to be located at or, in some RAM types, a unit of data called a page is read. The data that is read is transmitted along the data lines to the processor's nearby data buffer known as level-1 cache and another copy may be held in level-2 cache.

4

For video RAM, the process is similar to DRAM except that, in some forms of video RAM, while data is being written to video RAM by the processor, data can simultaneously be read from RAM by the video controller (for example, for refreshing the display image).

HOW RAM EFFECTIVENESS IS MEASURED:The amount of time that RAM takes to write data or to read it once the request has been received from the processor is called the access time. Typical access times vary from 9 nanoseconds to 70 nanoseconds, depending on the kind of RAM. Although fewer nanoseconds is better, user-perceived performance is based on coordinating access times with the computer's clock cycles. Access time consists of latency and transfer time. Latency is the time to coordinate signal timing and refresh data after reading it.

TYPES OF RAM:The following are some common types of RAM:

SRAM: Static random access memory uses multiple transistors, typically four to six, for each memory cell but doesn't have a capacitor in each cell. It is used primarily for cache.

DRAM: Dynamic random access memory has memory cells with a paired transistor and capacitor requiring constant refreshing.

FPM DRAM: Fast page mode dynamic random access memory was the original form of DRAM. It waits through the entire process of locating a bit of data by column and row and then reading the bit before it starts on the next bit. Maximum transfer rate to L2 cache is approximately 176 MBps.

EDO DRAM: Extended data-out dynamic random access memory does not wait for all of the processing of the first bit before continuing to the next one. As soon as the address of the first bit is located, EDO DRAM begins looking for the next bit. It is about five percent faster than FPM. Maximum transfer rate to L2 cache is approximately 264 MBps.

SDRAM: Synchronous dynamic random access memory takes advantage of the burst mode concept to greatly improve performance. It does this by staying on the row containing the requested bit and moving rapidly through the columns, reading each bit as it goes. The idea is that most of the time the data needed by the CPU will be in sequence. SDRAM is about five percent

5

faster than EDO RAM and is the most common form in desktops today. Maximum transfer rate to L2 cache is approximately 528 MBps.

DDR SDRAM: Double data rate synchronous dynamic RAM is just like SDRAM except that is has higher bandwidth, meaning greater speed. Maximum transfer rate to L2 cache is approximately 1,064 MBps (for DDR SDRAM 133 MHZ).

RDRAM: Rambus dynamic random access memory is a radical departure from the previous DRAM architecture. Designed by Rambus, RDRAM uses a Rambus in-line memory module (RIMM), which is similar in size and pin configuration to a standard DIMM. What makes RDRAM so different is its use of a special high-speed data bus called the Rambus channel. RDRAM memory chips work in parallel to achieve a data rate of 800 MHz, or 1,600 MBps. Since they operate at such high speeds, they generate much more heat than other types of chips. To help dissipate the excess heat Rambus chips are fitted with a heat spreader, which looks like a long thin wafer. Just like there are smaller versions of DIMMs, there are also SO-RIMMs, designed for notebook computers.

Credit Card Memory: Credit card memory is a proprietary self-contained DRAM memory module that plugs into a special slot for use in notebook computers.

PCMCIA Memory Card: Another self-contained DRAM module for notebooks, cards of this type are not proprietary and should work with any notebook computer whose system bus matches the memory card's configuration.

CMOS RAM: CMOS RAM is a term for the small amount of memory used by your computer and some other devices to remember things like hard disk settings -- see Why does my computer need a battery? for details. This memory uses a small battery to provide it with the power it needs to maintain the memory contents.

VRAM: VideoRAM, also known as multiport dynamic random access memory (MPDRAM), is a type of RAM used specifically for video adapters or 3-D accelerators. The "multiport" part comes from the fact that VRAM normally has two independent access ports instead of one, allowing the CPU and graphics processor to access the RAM simultaneously. VRAM is located on the graphics card and comes in a variety of formats, many of which are proprietary. The amount of VRAM is a determining factor in the resolution and color depth of the display. VRAM is also used to hold graphics-specific information such as 3-D geometry data and texture maps. True multiport VRAM tends to be expensive, so today, many graphics cards use SGRAM

6

(synchronous graphics RAM) instead. Performance is nearly the same, but SGRAM is cheaper.

TYPES OF RAM ACCORDING TO TECHNIQUE AND WORKING:

Your computer probably uses both static RAM and dynamic RAM at the same time, but it uses them for different reasons because of the cost difference between the two types. If you understand how dynamic RAM and static RAM chips work inside, it is easy to see why the cost difference is there, and you can also understand the names.

Dynamic RAM is the most common type of memory in use today. Inside a dynamic RAM chip, each memory cell holds one bit of information and is made up of two parts: a transistor and a capacitor. These are, of course, extremely small transistors and capacitors so that millions of them can fit on a single memory chip. The capacitor holds the bit of information -- a 0 or a. 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. 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.

Static RAM uses a completely different technology. In static RAM, a form of flip-flop holds each bit of memory (see How Boolean Gates Work for detail on flip-flops). A flip-flop for a memory cell takes 4 or 6 transistors along with some wiring, but never has to be refreshed. This makes static RAM significantly faster than dynamic RAM. However, because it has more parts, a static memory cell takes 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. So static RAM is fast and expensive, and dynamic RAM is less expensive and slower. Therefore static RAM is used to create the CPU's speed-sensitive cache, while dynamic RAM forms the larger system RAM space.

SPEED OF RAM:7

Speed of ram is also important. Speed is measured in Mega Hertz (MHz). Sometime its in Giga Hertz (GHz). Speed of RAM ranges from 400MHz to 1000MHz. It is also necesory for processor processing speed.Another measurement of speed is CAS Speed which is measured in nanosecond or

ns. It comes in 3 to 5ns.

TYPE OF RAM ACCORDING TO

SPEED:

There are three types of Rams used now a day

DDR (used in computers lasting 4 years)DDR2 (used in computers lasting 2 years)DDR3 (used in computers Now a day)

The difference in the RAMs is their bus speed and bandwidth.Manufacturers sale the rams according to Band Width and Bus speedFor example. PC3200 is bandwidth and 400MHz is Bus speed

RAM BANDWIDTH AND SPEED ANYLYSIS:

.

8

DDR2-RAM SPEEDPC2-3200 400MHzPC2-4200 533 MHzPC2-5300 667 MHzPC2-6400 800 MHzPC2-8000 1000 MHz

DDR-RAM SpeedPC1600 200MHzPC2100 266MHzPC2400 300MHzPC2700 333 MHzPC3000 375 MHzPC3200 400 MHzPC3500 433 MHzPC3700 466 MHzPC4000 500 MHzPC4300 533 MHzPC4500 566 MHzPC4800 600 MHz

DDR3-RAM SPEEDPC3-6400 800MHzPC3-8500 1062 MHzPC3-10600 1325 MHzPC3-12800 1600 MHz

MEMORY MODULES:

The type of board and connector used for RAM in desktop computers has 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 30-pin connector and was about 3.5 x .75 inches in size (about 9 x 2 cm). 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. For example, you would install two 8-megabyte (MB) SIMMs to get 16 megabytes total RAM. 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 4.25 x 1 inch (about 11 x 2.5 cm), used a 72-pin connector for increased bandwidth and allowed for up to 256 MB of RAM.

SIMM Memory Module

DIMM Memory Module

SODIMM Memory Module

As processors grew in speed and bandwidth capability, the industry adopted a new standard in dual in-line memory module (DIMM). With a whopping 168-pin or 184-pin connector and a size of 5.4 x 1 inch (about 14 x 2.5 cm), DIMMs range in capacity

9

from 8 MB to 1 GB per module and can be installed singly instead of in pairs. Most PC memory modules and the modules for the Mac G5 systems operate at 2.5 volts, while older Mac G4 systems typically use 3.3 volts. Another standard, Rambus in-line memory module (RIMM), is comparable in size and pin configuration to DIMM but uses a special memory bus to greatly increase speed. Many brands of notebook computers use proprietary memory modules, but several manufacturers use RAM based on the small outline dual in-line memory module (SODIMM) configuration. SODIMM cards are small, about 2 x 1 inch (5 x 2.5 cm), and have 144 or 200 pins. Capacity ranges from 16 MB to 1 GB per module. To conserve space, the Apple iMac desktop computer uses SODIMMs instead of the traditional DIMMs. Sub-notebook computers use even smaller DIMMs, known as MicroDIMMs, which have either 144 pins or 172 pins. Most memory available today is highly reliable. Most systems simply have the memory controller check for errors at start-up 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

OPPOSITE OF RAM:The opposite of RAM is serial access memory (SAM). SAM stores data as a series of memory cells that can only be accessed sequentially (like a cassette tape). If the data is not in the current location, each memory cell is checked until the needed data is found. SAM works very well for memory buffers, where the data is normally stored in the order in which it will be used (a good example is the texture buffer memory on a video card). RAM data, on the other hand, can be accessed in any order.

STRUCTURE OF RAM:The invention is an integrated circuit data storage array with storage cells disposed in an array of rows and columns with each cell having a number of sub cells. The physical location of the sub cells substantially reduces the space taken by horizontal data line used

10

for accessing columns. This is accomplished by locating sub cells of the same row number, the same bit number, and different column number adjacent to each other in the horizontal direction. So, a horizontal data line only extends between adjacent sub cells and significantly reduces the wasted layout of multibit horizontal data lines.

How Much RAM 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. Next to the CPU itself, RAM is the most important factor in computer performance. If you don't have enough, adding RAM can make more of a difference than getting a new CPU! If your system responds slowly or accesses the hard drive constantly, then you need to add more RAM. If you are running Windows XP, Microsoft recommends 128MB as the minimum RAM requirement. At 64MB, you may experience frequent application problems. For optimal performance with standard desktop applications, 256MB is recommended. If you are running Windows 95/98, you need a bare minimum of 32 MB, and your computer will work much better with 64 MB. Windows NT/2000 needs at least 64 MB, and it will take everything you can throw at it, so you'll probably want 128 MB or more. Linux works happily on a system with only 4 MB of RAM. If you plan to add X-Windows or do much serious work, however, you'll probably want 64 MB. Mac OS X systems should have a minimum of 128 MB, or for optimal performance, 512 MB. The amount of RAM listed for each system above is estimated for normal usage -- accessing the Internet, word processing, standard home/office applications and light entertainment. If you do computer-aided design (CAD), 3-D modeling/animation or heavy data processing, or if you are a serious gamer, then you will most likely need more RAM. You may also need more RAM if your computer acts as a server of some sort (Web pages, database, application, FTP or network). Another question is how much VRAM you want on your video card. Almost all cards that you can buy today have at least 16 MB of RAM. This is normally enough to operate in a typical office environment. You should probably invest in a 32-MB or better graphics card if you want to do any of the following:

Play realistic games Capture and edit video Create 3-D graphics Work in a high-resolution, full-color environment Design full-color illustrations

When shopping for video cards, remember that your monitor and computer must be capable of supporting the card you choose.

11