How to Measure

How to measure Data Data inside the computer is represented in form of electrical pulses, when high voltage is often denoted by 1 (or on) and low voltage is denoted by 0 (or off). Because we are using only two digits, 0 and 1, for data representation we are actually using the binary number system, where 0 and 1 are often referred to as binary digits. The abbreviation of “binary digit”, bit, is accepted as a basic unit when we measure amounts of information. All keys on the are coded with the combination of 0s and 1s. When you press any key, a corresponding sequence of 0s and 1s is sent to the memory inside the computer (see an example of what happens when a user presses keys on a keyboard). When a computer gets the sequence of binary digits, how can it know when the first character stops and the next one starts? The easiest solution was to make all characters to consist of the same number of digits. But how many digits? First how many character do we need to code? 26 upper case letters, 26 lower case letters, 10 decimal digits, punctuation and lots of special characters. Altogether to cover all these characters and all keys on the keyboard we need 256 codes. With one digit we can code two characters only. With two one digit we can code two characters only. With two digits we can code 22 = 4 characters. If we proceed this way, we’ll get following table of powers of 2:

21 = 2 22 = 2 23 = 8 24 = 16

25 = 32 26 = 64 27 = 128 28 = 256

From the table we can see than to represent 256 characters we need digits. What to do if the binary representation of a character is less than 8 digits? For example, upper case letter A Is coded as 65 using decimal system which is 1000001in binary. There are only 7 digits here. Place leading 0 ( zero) and you get 8 digits without changing the actual value of the number (like in decimal system 5,05 or 005 will have the same value). So every character occupies 8 bits of memory or 8 bits of secondary storage. The word “ HELLO” consists of 6 characters(5 letters and one full stop) and occupies 6*8=48 bits. The word “computer” consists of 8 characters and occupies 8*8=64 bits. Whatever amount of information you measure in bits, you will always get a multiple of 8. That is why another unit of measure, called byte, was introduced. Go to top of page A group of 8 bits is called a byte. As amounts of data being processed keep growing, other units of measure were created.

1 kilobyte = 1024 bytes. Outside computing, a kilo means 10000. However, in computer environment, all measures should be powers of 2 and closest to 1000 which is 210 . Kilobyte is often abbreviated as K or K byte. Today computer memory is measured in thousands of kilobytes or Megabytes and secondary storage is measured in millions of kilobytes or Gigabytes. A Megabyte is often represented as M byte or M. A Gigabyte is abbreviated as G. 1 Megabyte = 1024 K = 10242 bytes 1 Gigabyte = 1024 M = 10242 K = 10243 bytes 1 Terabyte = 1024 G = 10242 M = 10243 K = 10244 bytes In programming languages, a variable is named memory location created to keep data. But what amount of data? This depends on the type of the variable. If a variable is of type character, it will occupy only 1 byte of memory. A variable of type integer on a personal computer in most programming environments will occupy 2 bytes of memory. For example, if variable named Number is of type character and holds the value of ‘4’ it will occupy only one byte. But if it is of type integer with the value 4, it will occupy 2 bytes.

Factors that Influence Personal Computers Performance 1. The CPU High performance, copatibility and up gradability are features that are important. The higher the generation, the better. For example, because of high performance new features, Pentium 75 (fifth generation with the clock rate 75 MHz) Will out perform 80486DX100( which is the fourth generation CPU with the clock rate 100Mhz).

Another important feature is word size measured in bits. 80386 and 80486 Processors are 32 bet whereas Pentiums are 64 bit processors, thus Pentiums can transfer twice as much data at a time compared to third and fourth generation CPUs. 2. Clock rate. Since any step of processing can happen only on the “tick” Of the clock (called Clock cycle), the faster the rate quicker the CPU works. The 486 (TM) processor, for example, is able to execute many of its instructions in one clock cycle, while previous generations of Intel microprocessors require multiple clock cycles to execute a single instructions per clock cycle due to the fact that the Pentium processor’s two pipelines can execute two instructions simultaneously. If other modules of the system require more than one clock pulse, the CPU has to wait for them to keep up. This is called a wait state. 3. RAM It does not make much sense to have a fast processor if you don’t have fast RAM But note : faster RAM is more expensive. The amount of RAM is also important. Today, advanced operating systems require at least 4 megabytes of memory just to boot up a computer. Using more than one application at a time requires at least 8 megabytes, and reasonable performance today calls for 16 megabytes or more. The benefits of adding more RAM include letting you open more applications at the same time, and working with large file or documents. More memory may also make your machine run much faster. The quality of DRAM chips used in a memory module is the must important component in determining the overall quality and reliability of RAM. So which chips to consider? Enhanced Data Output (EDO) DRAM provides faster data throughput. Systems using EDO DRAM will be faster than similar systems using regular DRAM. EDO DRAM provides even higher performance benefit when used with an L2 cache. Enhanced DRAM (EDRAM)can be thought of as RAM than carries its own cache on each module. In an EDRAM-based system, essentially entire system memory bank is the cache. This can provide dramatic performance improvements. However, at this time, EDRAM is Scarce, very expensive and has not been adopted by many system vendors. 4. Cache presence and size L1 Cache.

The bigger the on-chip cache size, the better since more instructions and data can be stored on the chip, reducing the number of times the processor has to access slower, off-chip memory areas to get data. For example, Intel has doubled on-chip cache size to 32K on the Intel Pentium processor with MMX technology. L2 Cache. System memories composed of dynamic RAM (DRAM) alone have not been able to keep up with the dramatic increases in CPU speeds over the years. In order to optimize the memory performance in these systems, designers are implementing architectures using cache memory, resulting in speed increases up to 45%. Expanding secondary cache (e.g. from 128K to 512K) can greatly improve the performance of some applications. In a recent industry magazine test of notebook computers, a 486 machine with L2 cache outperformed a Pentium90 machine without L2 cache by 30%. 5. Data bus type and size. The data bus is the highway than carries information between the processor and the memory subsystem. The wider the data bus, the more information it can transfer. Because of its external 64-bit data bus, the Pentium processor can transfer data to and from memory at rates up to 528 Mbytes/second (five times faster than the transfer rate of the Intel 1486 (TM) DX2-66MHz microprocessor) The PCI local bus greatly improves I/O performance. It can transfer data between the processor and the peripherals at up to 132 MB/second, far faster Than the ISA bus rate of 5 MB/ second. 6. Hard disk capacity can seek time. High-performance hard drives have at least 1.2 G of capacity, provide an average Seek time of 12 milliseconds, a 128 to 256 K hard disk buffer cache with both write-caching and read-caching capabilities, and spin about 4,500 rotations per minute. (You may be familiar with using a disk cache, such, such as Microsoft Smart Drive, which uses a small RAM buffer to speed up access to a large hard disk.) 7. Videocard. A full-featured PCI-compliant VGA card, with at least 1 to 2 MB of video RAM, will further accelerate graphics performance. 8. CD-ROM drive speed. At the time of writing of these notes the slowest CD-ROM drive available on the market is quad speed. It may be enough, if you are not running applications from

CD-ROM, but only installing them. Otherwise look at octal or ten-speed technologies. 9. MMX processors Multimedia extensions processors (MMX) is designed specifically to support media-rich software and communications applications. The Pentium processor with MMX technology will give a better, smoother and more realistic multimedia experience. These processors have got 57 powerful new instructions specifically designed to manipulate and process video, audio and graphical data efficiently. However, your system will require software designed for MMX technology (old software must be recompiled to take advantage of new MMX features). Remember that the key measurement is how your software performs on a given system versus that system’s, service and warranty, reliability and compatibility. So first decide what software you will need, look at the minimum hardware requirements for the software to run and then make your decisions about what hardware you will need. To help you make your decisions, following is the list of computer-intensive applications: -Database packages -Computer-aided design/engineering -3-D modeling -Large-scale financial analysis -High-throughput client/server -Network applications -Virtual reality -Rich electronic mail