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SHA-256 hash function. Smart contracts use 256- or 257-bit integers; 256-bit words for the Ethereum Virtual Machine. "We realize that a 257 bits byte is quite unusual, but for smart contracts it is ok to have at least 256 bits numbers. The leading VM for smart contracts, Ethereum VM, introduced this practice and other blockchain VMs followed." [8]
[citation needed] Thus it made sense to have few registers and use the main memory as an extended pool of extra registers. In machines with a relatively wide 16-bit address bus and comparatively narrow 8-bit data bus, calculating an address in memory could take several cycles. The zero page's one-byte address was smaller and therefore faster to ...
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 (page-sized) structure, which is by default located exactly before offset 0 of the program's load segment, rather than in segment 0.
As a result, the last page will likely only be partially full, wasting some amount of memory. Larger page sizes lead to a large amount of wasted memory, as more potentially unused portions of memory are loaded into the main memory. Smaller page sizes ensure a closer match to the actual amount of memory required in an allocation.
Consider a main memory of 16 kilobytes, which is organized as 4-byte blocks, and a direct-mapped cache of 256 bytes with a block size of 4 bytes. Because the main memory is 16kB, we need a minimum of 14 bits to uniquely represent a memory address. Since each cache block is of size 4 bytes, the total number of sets in the cache is 256/4, which ...
It only offered 256 bytes of memory. The clock speed was 1 MHz, but the program speed averaged below 1,000 instructions per second due the many clock cycles needed for each operation and slow access to serial memory.
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.
The zero-page, the first 256 bytes of memory that were used as pseudo-registers, could now be moved to any page in main memory using the B(ase page) register. The stack register was widened from 8 to 16-bits using a similar page register, SPH (stack pointer high), allowing the stack to be moved out of page one and to grow to larger sizes.