Byte

As was said in the introduction (Section 2.1), chemical structures are the universal and the most natural language of chemists, but not for computers. Computers woi k with bits packed into words or bytes, and they perceive neither atoms noi bonds. On the other hand, human beings do not cope with bits very well. Instead of thinking in terms of 0 and 1, chemists try to build models of the world of molecules. The models ai e conceptually quite simple 2D plots of molecular sti uctures or projections of 3D structures onto a plane. The problem is how to transfer these models to computers and how to make computers understand them. This communication must somehow be handled by widely understood input and output processes. The chemists way of thinking about structures must be translated into computers internal, machine representation through one or more intermediate steps or representations (sec figure 2-23, The input/output processes defined... 

The ciphered code is indicated with a defined length, i.e., a fixed hit/byte length. A hash code of 32 bits could have 2 (or 4 294 976 296) possible values, whereas one of 64 bits could have 2 values, However, due to tbe fixed length, several diverse data entries could assign the same hash code ( address collision ), The probability of collision rises if the number of input data is increased in relation to the range of values (bit length). In fact, the limits of hash coding are reached with about 10 000 compounds with 32 bits and over 100 million with 64 bits, to avoid collisions in databases [97. ... 

Figure 5-3. a) Main organization of a database or container the basic units of a field are bits and bytes, b) Example of data organization in a flat-file. 

Java Virtual Machine miming on the system. Mechanisms like JIT (Just in Time Compiler - parts of the byte code were compiled into machine code) or JNI (Java Native Interface - enables the use of fast libraries resulting from compiled C+ + Code within a Java program) can be used to reduce this characteristic disadvantage. 

IlyperChem uses 16 bytes (two double-precision words) of storage for each electron repulsion integral. The first 8 bytes save thecom-pressed four indices and the second S bytes store the value of the integral. Each index lakes 16 bits. Thus the maximum number of basis fiinctions is 65,535. This should satisfy all users of IlyperChem for the foreseeable future. 

Program MOCOEFS This program is designed to read in (from the keyboard) the LCAO-MO eoeffieient matrix and write it out to disk. Alternatively, you ean ehoose to have a unit matrix (as your initial guess) put out to disk. With the program 1 imitations deseribed above, MOCOEFS memory usage is 2744 bytes. 

With the program limitations deseribed above, FNCT MAT memory usage is 1960040 bytes. 

Program FOCK This program is designed to read in the LCAO-MO eoeffieient matrix, the one- and two-eleetron AO integrals and to form a elosed shell Foek matrix (i.e., a Foek matrix for speeies with all doubly oeeupied or bitals). With the program limitations deseribed above, FOCK memory usage is 255256 bytes. 

Program UTMATU This program is designed to read in a real matrix. A, a real transformation matrix, B, perform the transformation X = B(transpose) A B, and output the result. With the program limitations deseribed above, UTMATU memory usage is 1960040 bytes. 

With the program limitations described above, FENERGY memory usage is 1905060 bytes.. 

Bits are put together as bytes. This example is an 8-bit byte. Faster, more powerful computers have more bits to the byte (16, 32, 64). In reading a byte, the bits flow one after the other out of the byte as electronic pulses (a positive voltage for on and zero for off). 

The previous discussion concentrated on arithmetical operations by computing in binary numbers represented as bits and bytes. However, other computer functions also use bytes of information. 

By electronic engineering, a system of interconnected switching devices is able to respond in one of only two modes (on or off), and these modes can be controlled at the basic level of a bit. Bits are assembled into bytes, as with an 8-bit device, and through programming of the bytes a computer central processor can be made to follow sets of instructions (programs) written in special languages, either at a direct level (machine code) that can be acted upon immediately by a computer or at a high level that is translated for the user into machine code. 

Movement of information in a computer could be likened to a railway system. Carriers of information (bits or bytes) move together (like a train and wagons) from one location to another along electronic tracks. It is important that no two bits of information are mixed up, and therefore all the moves must be carefully synchronized with a clock. This situation resembles the movement of trains on a railway many trains use the same track but are not all in the same place at the same time. The railways run to a timetable. Similarly, information is moved around the computer under the control of the central processor unit (CPU). 

The capacity of a computer to carry out various tasks is partly governed by the number of bytes it has. Thus, a one-megabyte memory means there are 1 million locations with 8, 16, 32, or 64 bits in each. 

M. D. Lechner and co-workers, Makromol Kolloq., Ereiburg, Germany, 1985, Congress Book, p. 78 T. Parish, BYTE 15, 283 (1990). 

Blt-M ppedImages. A bit map is a grid pattern composed of tiny cells or picture elements called pixels. Each pixel has two attributes a location and a value or set of values. Location is defined as the address of the cell in a Cartesian, ie, x andjy coordinate, system. Value is defined as the color of the pixel in a specified color system. Geometric quaUties of images are a function of the location attribute, ie, the finer the grid pattern, the more precisely can the geometric quaUties be controlled. Color quaUties are a function of the value attribute, ie, the more bytes of computer memory assigned to describe each pixel, the more precisely can the color quaUties be controlled. 

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