More on memories
Last week we started discussing Random Access Memory (RAM) by looking at how it differs from ROM and made a brief comparison of its functions and performance with other types of primary storage devices. I mentioned that there are two main types of RAM: static and dynamic, and this week we will continue to dig deeper into the subject.

Static RAM (SRAM)
Static RAM is a type of RAM that holds its data for as long as power is supplied to the circuit. This differs from dynamic RAM (DRAM) on the grounds that DRAM must be refreshed with electronic pulses many times per second in order to hold its data contents. SRAM is used for specific applications within the PC, where its strengths outweigh its weaknesses compared to DRAM.

SRAM doesn’t require external refresh circuitry to keep data intact and is faster than DRAM. Yet SRAM is several times more expensive than DRAM and takes up much more space than DRAM. Advantages and disadvantages considered, SRAM is capable of superior performance when compared to DRAM, and it is used exclusively when it is economically feasible to do so. Unfortunately, SRAM is prohibitively large and costly, which is why DRAM is used for system memory. SRAM is used instead for level 1 cache (small holders of memory within the processor) and level 2 cache memory (small portions of memory placed just outside the processor) for which it is better suited. Level 1 and level 2 cache memory needs to be very fast, and in small quantities.

SRAM is manufactured in a similar way to how processors are made. They are highly integrated transistor patterns that have been etched into silicon using a special kind of light. Each SRAM bit is made up between four to six transistors. That is why SRAM takes up more space compared to DRAM, which uses only one transistor and a capacitor. SRAM chips are comprised of thousands or millions of identical cells. Therefore they are much easier to make than a CPU, which is a large die with a complex structure of transistors arranged in many forms. This is one reason why RAM chips cost much less than processors do.

Dynamic RAM (DRAM)
Dynamic RAM is a type of RAM that only holds its data if it is continuously refreshed by a special circuit. This circuitry reads the contents of each memory cell hundreds of times each second. This is done regardless of whether the memory cell is being used at that time by the computer or not. Due to the way in which the cells are constructed, the reading action itself refreshes the contents of the memory. If this is not done regularly, then the DRAM will lose its contents, even if it continues to have power supplied to it. This refreshing action is why the memory is called dynamic.

All PCs use DRAM for their main system memory, instead of SRAM, even though DRAM is slower than SRAM and requires the overhead of the refresh circuitry. It may seem weird to want to make the computer’s memory out of something that can only hold a value for a fraction of a second. In fact, DRAM is both more complicated and slower than SRAM.

The reason that DRAM is used is simple. DRAM is much cheaper to produce and takes up less than 1/4 the silicon volume of SRAM. The overhead of the refresh circuit is tolerated in order to allow the use of large amounts of inexpensive, compact memory. The refresh circuitry itself is almost never a problem; many years of using DRAM has caused the design of these circuits to be almost ‘perfect’.

DRAM is manufactured using a similar process to how processors are made. A silicon substrate is etched with the patterns that make the transistors, capacitors and support structures that comprise each ‘bit’. DRAM costs much less than a processor because it is a series of simple, repeated structures, so the complexity of making a single chip with several million individually located transistors is avoided.

There are many different kinds of specific DRAM technologies and speeds that they are available in. These have evolved over many years resulting in many different types and variations of DRAM, which we will discuss next week. Till then write in and share the experience! Source: PC Hardware Guide

Improve your computer literacy
POP
(1) Short for Post Office Protocol, a protocol used to retrieve e-mail from a mail server. Most e-mail applications (sometimes called an e-mail client) use the POP protocol, although some can use the newer IMAP (Internet Message Access Protocol).
There are two versions of POP. The first, called POP2, became a standard in the mid 80s and requires SMTP to send messages. The newer version, POP3, can be used with or without SMTP.

(2) Short for point of presence, an access point to the Internet. ISPs have typically multiple POPs. A point of presence is a physical location, either part of the facilities of a telecommunications provider that the ISP rents or a separate location from the telecommunications provider that houses servers, routers, ATM switches and digital/analog call aggregators. Webopedia.com

Did you know?
Fibonacci numbers were originally defined by the Italian mathematician Fibonacci (aka Leonardo da Pisa) in the 13th century to model the growth of rabbit populations. They are a series of whole numbers in which each number is the sum of the two preceding numbers. Beginning with 0 and 1, the sequence of Fibonacci numbers would be 0,1,1, 2, 3, 5, 8, 13, 21, 34, etc. using the formula n = n (-1) + n (-2), where the n (-1) means “the last number before n in the series” and n (-2) refers to “the second last one before n in the series.”

In computer programming, Fibonacci numbers give a model for designing recursive programming algorithms where the time for any routine is the time within the routine itself, plus the time for the recursive calls.

News in the techno world
Microsoft hints about Windows ‘Longhorn’
Billed to be the biggest release of Microsoft’s flagship product since Windows 95, Longhorn will include technology for building a new generation of ‘smart client’ software that combines the look and feel of PC applications such as Word or Excel with immediate access to information on the Web.

Longhorn also is supposed to address many of the problems that dog PC users, including viruses and worms, and help them deal with the difficulty of searching across an array of files, e-mails, Web pages, and photos strewn across ever-larger hard drives. Everything that gets written for Windows will be in Net code, which is supposed to help prevent developer errors that can lead to unsecured applications, according to Microsoft.

New database technology in Windows could let users automatically poll the operating system for groups of files, e-mails, calendar entries, and other documents that match certain criteria, instead of relying on their memory to set up stacks of hierarchical folders. Windows Longhorn is due to be released in 2006.

Digitally dead
Generations of dead people in a cemetery in southern France have joined the information age, thanks to a new computerized system that maps the way to graves and enables people to leave electronic condolence messages. People arriving this week at the cemetery in Saint Andre de la Roche, near Nice, found an interactive screen giving precise locations and personal details for the 4,000 deceased.

Visitors can read biographies of the deceased, type in messages of sympathy and also find contact details for local taxis or funeral parlours. Florists are also said to be delighted by an innovation that makes it easier to turn up at the right place with deliveries. Source: News.google.com

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