Memory Addressing
The memory of a computer system consists of tiny electronic switches, with each switch in one of two states: open or closed. It is, however, more convenient to think of these states as 0 and 1, rather than open and closed. Thus, each switch can represent a bit. The memory unit consists of millions of such bits. In order to make memory more manageable, eight bits are grouped into a byte. Memory can then be viewed as consisting of an ordered sequence of bytes. Each byte in this memory is identified by its sequence number starting with 0, as shown in Figure 1. This is referred to as the memory address of the byte. Such memory is called byte addressable memory because each byte has a unique address.
The Pentium can address up to 4 GB (232 bytes) of main memory (see Figure 1). This magic number comes from the fact that the address bus of the Pentium has 32 address lines. This number is referred to as the memory address space. The memory address space of a system is determined by the address bus width of the processor used in the system. The actual memory in a system, however, is always less than or equal to the memory address space. The amount of memory in a system is determined by how much of this memory address space is populated with memory chips.
Memory chips:
It is possible to visualize a typical internal main memory structure as consisting of rows and columns of basic cells. Each cell is capable of storing one bit of information. Figure 2 provides a conceptual internal organization of a memory chip. In this figure, cells belonging to a given row can be assumed to form the bits of a given memory word. Address lines A0A1 . . . An-2An-1 are used as inputs to the address decoder in order to generate the word select lines W0 W1. . .W2n-1. A given word select line is common to all memory cells in the same row. At any given time, the address decoder activates only one word select line while deactivating the remaining lines. A word select line is used to enable all cells in a row for read or write. Data (bit) lines are used to input or output the contents of cells. Each memory cell is connected to two data lines. A given data line is common to all cells in a given column.
المادة المعروضة اعلاه هي مدخل الى المحاضرة المرفوعة بواسطة استاذ(ة) المادة . وقد تبدو لك غير متكاملة . حيث يضع استاذ المادة في بعض الاحيان فقط الجزء الاول من المحاضرة من اجل الاطلاع على ما ستقوم بتحميله لاحقا . في نظام التعليم الالكتروني نوفر هذه الخدمة لكي نبقيك على اطلاع حول محتوى الملف الذي ستقوم بتحميله .
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