Two major components of the electronic equipment of the computer - its central processor (CPU) and its memory. Other components (disk drives, the keyboard, displays, printers, etc.) are external in relation to the computer. These external components of the electronic equipment are called as PERIPHERALS or it is simple DEVICES.
Access to memory will be organized by connection of contents of one of registers of a segment with contents of one of the remained registers. Value of the segment register is called as the segment address. Value of other registers in this case is called as the relative address of a cell of memory (from the beginning a segment or its short address. In such way, the address of byte is calculated by means of multiplication of the address of a segment on 16, and the short address is added to the received value.
At turning on of the machine (or restart of system) control is transferred to the ROM program (reading only memory). The program checks correctness of structure of record of start of operational system on a system disk. If record is found and does not contain mistakes, it is loaded into memory and receives management.
The processor of the computer (CPU) divides memory into the blocks called by segments. Each segment borrows 64 K and to each segment there corresponds the unique numerical address. The processor has four registers of a segment. The register is the internal structure intended for storage of information. Registers of a segment are intended for storage of addresses of separate segments. They are called as CS (a segment a code, DS (a segment of data), SS (a segment the stack and ES (a spare segment). Except specified, the processor has 9 more registers. At present it should be noted the registers IP (the index of team) and SP (the index the stack. The registers CS and IP in couple make the long address of command which will be executed by the following. The registers SS and SP in couple make the long address
The hard drive consists of one or several round plates. For storage of information both surfaces of a plate are used. Each surface breaks into paths, paths, in turn, - on sectors. Paths of identical radius make the cylinder. Thus, all zero paths make the cylinder with number zero, paths with number 1 - the cylinder with number 1, etc.
For input of information in most cases use the keyboard. As a result of performance of the majority of operations the obtained data are displayed the display. Therefore the keyboard is considered the standard input equipment, and the screen - the standard output equipment.
Index register too two. The registers SI and DI are applied in a combination with one of segment registers and define location of a concrete cell of memory. The register SI is combined usually with the register DS, the register DI - with the register ES.
There are two registers of the stack. They are applied in a combination with the register SS and define location of the stack. The register SP is called as the index of the beginning of the stack, and in a combination with the register SS identifies the first byte of the stack. The register BP is called as the index of base of the stack and in a combination with the register SS identifies the last byte of the stack.