Memory Management and Microprocessor

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In this paper, we will cover the memory management of Windows NT which will be covered in first section, and microprocessors which will be covered in second section. When covering the memory management of Windows NT, we will go through physical memory management and virtual memory management of that operating system. In virtual memory management section, we will learn how Windows NT managing its virtual memory by using paging and mapped file I/O.

After covering the memory management, we will go through microprocessor. In this section, we will learn a bit about the recent microprocessors, such as Intel and AMD microprocessors. We also will learn about the trends that affecting the performance of microprocessors.

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The segmentation scheme in Intel 80386 microprocessor is more advanced than that in Intel 8086 microprocessor. The 8086 segments start at a fixed location and are always 64K in size, but with 80386, the starting location and the segment size can separately be specified by the user.

The segments may overlap, it allows two segments to share address space. To send the necessary information, segment tables with segment selector as index are used. At any time, only two segment tables can be active. They are Global Descriptor Table (GDT) and a Local Descriptor Table (LDT). This two segment table only can be executed by the operating system.
Segment table is an array of segment descriptors which specify the starting address and the size of the segment. Each segment descriptor has 2 bits specifying its privilege level, called as the Descriptor Privilege Level (DPL). This DPL has to be compared with Requested Privilege Level (RPL) and Current Privilege Level (CPL) before processor grants the access to a segment. If the DPL of the segment is less than or equals to the RPL as well as the CPL, then the processor will grant access to a particular segment. This serves as protection mechanism for operating system.

1.2.2. Virtual Memory Management in Windows NT

Windows NT virtual memory manager provides large virtual memory space to applications via two memory management processes. They are called paging (moving data between
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