Compilers for the family commonly support two types of pointernear and far. Near pointers are bit offsets implicitly associated with the program's code or data segment and so can be used only within parts of a program small enough to fit in one segment. Far pointers are bit segment:
Many of the features of these earlier microprocessors are basically unchanged in the Pentium. The main change is in Memory management of microprocessors 8086 paging unit and a new system memory- management mode.
Paging Unit The paging mechanism functions with 4K-byte memory pages or with a new extension available to the Pentium with 4M-byte memory pages. As detailed in Chapters 1 and 17, the size of the paging table structure can become large in a system that contains a large memory.
Recall that to fully repage 4G bytes of memory, the microprocessor requires slightly over 4M bytes of memory just for the page tables. In the Pentium, with the new 4M-byte paging feature, this is dramatically reduced to just a single page directory and no page tables.
The new 4M-byte page sizes are selected by the PSE bit in control register 0. The main difference between 4K paging and 4M paging is that in the 4M paging scheme there is no page table entry in the linear address.
See Figure 18—10 for the 4M paging system in the Pentium microprocessor. Pay close attention to the way the linear address is used with this scheme. Notice that the leftmost 10 bits of the linear address select an entry in the page directory just as with 4K pages.
Unlike 4K pages, there are no page tables; instead, the page directory addresses a 4M-byte memory page. Memory-Management Mode The system memory-management mode SMM is on the same level as protected mode, real mode, and virtual mode, but it is provided to function as a manager.
The SMM is not intended to be used as an application or a system-level feature. It is intended for high-level system functions such as power management and security, which most Pentiums use during operation, but that are controlled by the operating system.
The SMI interrupt disables all other interrupts that are normally handled by user applications and the operating system. RSM returns from the memory-management mode interrupt and returns to the interrupted program at the point of the interruption.
This initial state can be changed using a jump to any location within the first 1M byte of the memory. An environment similar to real mode memory addressing is entered by the management mode interrupt, but it is different because, instead of being able to address the first 1M of memory, SMM mode allows the Pentium to treat the memory system as a flat, 4G-byte system.
In addition to executing software that begins at location H, the SMM interrupt also stores the state of the Pentium in what is called a dump record.
The dump record allows a Pentium-based system to enter a sleep mode and reactivate at the point of program interruption.
Table 18—2 lists the contents of the dump record. The SMM mode can be used by the system before the normal operating system is placed in the memory and executed. If the system relocates the SMRAM before booting the normal operating system, it becomes available for use in addition to the normal system.
When the first RSM instruction is executed, returning control back to the interrupted system, the new value from these locations changes the base address of the SMM interrupt for all future uses. For example, if the state dump base address is changed to.Note that the does not work the whole 1MB memory at any given time.
However it works only with four 64KB segments within the whole 1MB memory. Bellow is the one way of positioning four 64 kilobyte segments within the 1M byte memory space of an The microprocessor has 20 bit address bus and therefore memory locations. The pin diagram of is as shown: The microprocessor is just like microprocessor but the difference between them is that the microprocessor is of 8 bits but that of the is the 16 bit microprocessor.
microprocessor and memory management: At the most primitive level, a computer consists of a microprocessor, which executes instructions, and a memory, in which those instructions (and other data) is timberdesignmag.com shows a block diagram of these two components.
May 11, · Note that the does not work the whole 1MB memory at any given time. However it works only with four 64KB segments within the whole 1MB memory.
Bellow is the one way of positioning four 64 kilobyte segments within the 1M byte memory space of an Aug 12, · Many of the features of these earlier microprocessors are basically unchanged in the Pentium.
The main change is in the paging unit and a new system memory- management mode. Paging Unit. The paging mechanism functions with 4K-byte memory pages or with a new extension available to the Pentium with 4M-byte memory pages. Memory Management Memory management can become very complex in modern day computers as with the requirements for the management of the memory There are four categories that must be satisfied within memory management which are address mapping and relocation, protection and sharing, application organization, and two-level memory organization.