Search results
Results from the WOW.Com Content Network
In computer architecture, 256-bit integers, memory addresses, or other data units are those that are 256 bits (32 octets) wide. Also, 256-bit central processing unit (CPU) and arithmetic logic unit (ALU) architectures are those that are based on registers , address buses , or data buses of that size.
The size of a page depends on the context, and the significance of zero page memory versus higher addressed memory is highly dependent on machine architecture. For example, the Motorola 6800 and MOS Technology 6502 processor families treat the first 256 bytes of memory specially, [1] whereas many other processors do not.
For instance, many 8-bit processors, such as the MOS Technology 6502, supported 16-bit addresses— if not, they would have been limited to a mere 256 bytes of memory addressing. The 16-bit Intel 8088 and Intel 8086 supported 20-bit addressing via segmentation , allowing them to access 1 MiB rather than 64 KiB of memory.
One of the major improvements the PCI Local Bus had over other I/O architectures was its configuration mechanism. In addition to the normal memory-mapped and I/O port spaces, each device function on the bus has a configuration space, which is 256 bytes long, addressable by knowing the eight-bit PCI bus, five-bit device, and three-bit function numbers for the device (commonly referred to as the ...
In 8-bit CP/M versions it is located in the first 256 bytes of memory, hence its name. The equivalent structure in DOS is the Program Segment Prefix (PSP), a 256-byte structure, which, however, is by default located at offset 0 in the program's load segment (rather than in segment 0) immediately preceding a loaded program.
Designers of these processors included a partial remedy known as "zero page" addressing. The initial 256 bytes of memory ($0000 – $00FF; a.k.a., page "0") could be accessed using a one-byte absolute or indexed memory address. This reduced instruction execution time by one clock cycle and instruction length by one byte.
Some examples of improvements are: An expanded RAM module capable of storing 256 bytes, utilizing the entire 8-bit address space. With the help of segmentation registers, the RAM module can be further expanded to a 16-bit address space, matching the standard for 8-bit computers.
An example of this approach is the MOS 6502, which had only a single register, in which case it is referred to as the accumulator, and a special "zero page" addressing mode that treated the first 256 bytes of memory as if they were registers. Placing code and data in the zero page meant the instruction was only two bytes long instead of three ...