Английский язык для пользователей ПК и программистов - Гольцова Е.В.
ISBN 5-7931-0086-5
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TEXT III
The 8088 is the 16-bit microprocessor that controls the standard IBM personal computers, including the original PC, the PC/XT, the Portable PC, and the PCjr. Almost every bit of data that enters or leaves the computer passes through the CPU to be processed.
Inside the 8088, 14 registers provide a working area for data transfer and processing. These internal registers, forming an area 28 bytes in size, are able to temporarily store data, memory addresses, instruction pointers, and status and control flags. Through these registers, the 8088 can access 1 MB (megabyte), or more than one million bytes, of memory.
The 8086 is used in the PS/2 models 25 and 30 (and also in many IBM PC clones). The 8086 differs from the 8088 in only one minor respect: it uses a full 16-bit data bus instead of the 8-bit bus that the 8088 uses. (The difference between 8-bit and 16-bit buses is discussed below.) Virtually anything that you read about the 8086 also applies to the 8088; for programming purposes, consider them identical.
The 80286 is used in the PC/AT and in the PS/2 models 50 and 60. Although fully compatible with the 8086, the 80286 supports extra programming features that let it execute programs much more quickly than the 8086. Perhaps the most important enhancement to the 80286 is its support for multitasking.
Multitasking is the ability of a CPU to perform several tasks at a time — such as printing a document and calculating a spreadsheet — by quickly switching its attention among the controlling programs.
The 8088 used in a PC or PC/XT can support multitasking with the help of sophisticated control software.
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However, an 80286 can do a much better job of multitasking because it executes programs more quickly and addresses much more memory than the 8088. Moreover, the 80286 was designed to prevent tasks from interfering with each other.
The 80286 can run in either of two operating modes: real mode or protected mode. In real mode, the 80286 is programmed exactly like an 8086. It can access the same 1 MB range of memory addresses as the 8086. In protected mode, however, the 80286 reserves a predetermined amount of memory for an executing program, preventing that memory from being used by any other program. This means that several programs can execute concurrently without the risk of one program accidentally changing the contents of another program's memory area. An operating system using 80286 protected mode can allocate memory among several different tasks much more effectively than can an 8086-based operating system.
The PS/2 Model 80 uses the 80386, a faster, more powerful microprocessor than the 80286. The 80386 supports the same basic functions as the 8086 and offers the same protected-mode memory management as the 80286.
However, the 80386 offers two important advantages over its predecessors:
The 80386 is a 32-bit microprocessor with 32-bit registers. It can perform computations and address memory 32 bits at a time instead of 16 bits at a time.
The 80386 offers more flexible memory management than the 80286 and 8086.
Упражнение 40. Прочтите и переведите подчеркнутые слова и словосочетания:
The Intel486™ processor added more parallel execution capability by (basically) expanding the Intel386™ processor's Instruction Decode and Execution Units into five pipelined stages, where each stage (when needed) operates in parallel with the others on up to five instructions in different stages of execution. Each stage can do its work on one instruction in one clock, and so the Intel486™ processor can execute as rapidly as one instruction per CPU clock. An 8-KByte on-chip L1 cache was added to the Intel486™ processor to greatly increase the percent of instructions that could execute at the scalar rate of one per clock: memory access instructions were now included if the operand was in
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the L1 cache. The Intel486™ processor also for the first time integrated the floating-point math unit onto the same chip as the CPU and added new pins, bits, and instructions to support more complex and powerful systems (L2 cache support and multiprocessor support). Late in the Intel486™ processor generation, Intel incorporated features designed to support energy savings and other system management capabilities into the IA mainstream with the Intel486™ SL Enhanced processors. These features were developed in the Intel386™ SL and Intel486™ SL processors, which were specialized for the rapidly growing battery-operated notebook PC market. The features include the new System Management Mode, triggered by its own dedicated interrupt pin, which allows complex system management features (such as power management of various subsystems within the PC), to be added to a system transparently to the main operating system and all applications. The Stop Clock and Auto Halt Powerdown features allow the CPU itself to execute at a reduced clock rate to save power, or to be shut down (with state preserved) to save even more power.
