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A modern x86 CPU may use more than 4 GB of memory, either utilizing the native 64-bit mode of x86-64 CPU, or the Physical Address Extension (PAE), a 36-bit addressing mode. In such a case, a device using DMA with a 32-bit address bus is unable to address memory above the 4 GB line.
The 64 MB [6] of sound memory on the Sound Blaster X-Fi Fatality Pro sound card is built from two Micron 48LC32M8A2 SDRAM chips. They run at 133 MHz (7.5 ns clock period) and have 8-bit wide data buses. [10] Originally simply known as SDRAM, single data rate SDRAM can accept one command and transfer one word of data per clock cycle.
The IBM PC took a more conventional approach, their adaptor card could support up to four drives; on the PC direct memory access (DMA) to the drives was performed using DMA channel 2 and IRQ 6. The diagram below shows a conventional floppy disk controller which communicates with the CPU via an Industry Standard Architecture (ISA) bus or similar ...
Memory-mapped I/O is preferred in IA-32 and x86-64 based architectures because the instructions that perform port-based I/O are limited to one register: EAX, AX, and AL are the only registers that data can be moved into or out of, and either a byte-sized immediate value in the instruction or a value in register DX determines which port is the source or destination port of the transfer.
Intel 8237A-5, used on the original IBM PC motherboard Pinout. Intel 8237 is a direct memory access (DMA) controller, a part of the MCS 85 microprocessor family. It enables data transfer between memory and the I/O with reduced load on the system's main processor by providing the memory with control signals and memory address information during the DMA transfer.
Everyday PC usage can take its toll on computer and PC systems, making them annoyingly slow. System Mechanic, from iolo, is a software suite that secures, optimizes, repairs and fine tunes your computer after five restarts so the system can run faster and at its best. Sign up for System Mechanic
The bit-lines are precharged to exactly equal voltages that are in between high and low logic levels (e.g., 0.5 V if the two levels are 0 and 1 V). The bit-lines are physically symmetrical to keep the capacitance equal, and therefore at this time their voltages are equal. [35] The precharge circuit is switched off.
An attacker could, for example, use a social engineering attack and send a "lucky winner" a rogue Thunderbolt device. Upon connecting to a computer, the device, through its direct and unimpeded access to the physical address space, would be able to bypass almost all security measures of the OS and have the ability to read encryption keys, install malware, or control other system devices.