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The 80x86 IBM PC and Compatible Computers- P7

The 80x86 IBM PC and Compatible Computers- P7: Praised by experts for its clarity and topical breadth, this visually appealing, one-stop source on PCs uses an easy-to-understand, step-by-step approach to teaching the fundamentals of 80x86 assembly language programming and PC architecture. Offering users a fun, hands-on learning experience, it uses the Debug utility to show what action the instruction performs, then provides a sample program to show its application. | CHAPTER 10 MEMORY AND MEMORY INTERFACING Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. 265 This chapter explores memory and memory interfacing of the x86 PC. We first study the basics of semiconductor memory chips then in Section 10.2 we present memory address decoding using simple logic gates. The memory map and memory space allocation of the PC are discussed in Section 10.3. Section 10.4 explores the issue of data integrity in RAM and ROM. Section 10.5 discusses the CPU s bus cycle time for memory and shows how to calculate bus bandwidth. The specifics of memory cycle time for the ISA bus are covered in Section 10.6. SECTION 10.1 SEMICONDUCTOR MEMORY FUNDAMENTALS In the design of all computers semiconductor memories are used as primary storage for code and data. Semiconductor memories are connected directly to the CPU and they are the memory that the CPU first asks for information code and data . For this reason semiconductor memories are sometimes referred to as primary memory. The main requirement of primary memory is that it must be fast in responding to the CPU only semiconductor memories can do that. Among the most widely used semiconductor memories are ROM and RAM. Before we discuss different types of RAM and ROM we discuss terminology common to all semiconductor memories such as capacity organization and speed. Memory capacity The number of bits that a semiconductor memory chip can store is called its chip capacity. It can be in units of Kbits kilobits Mbits megabits and so on. This must be distinguished from the storage capacity of computers. While the memory capacity of a memory IC chip is always given in bits the memory capacity of a computer is given in bytes. For example an article in a technical journal may state that the 64M chip has become popular. In that case although it is not mentioned that 64M means 64 megabits it is understood since the article is referring to an IC memory chip. However if an advertisement .