Este o incursiune interesantă în istoria procesoarelor și a motivelor din spatele deciziilor de a folosi opt biți pentru un byte.
Fără a putea spune că am o înțelegere profundă a funcționării unui CPU, aș zice că o putere de-ale lui 2 ar fi o un număr mai potrivit decât… altceva. Dar asta este doar intuiția, fără a putea explica de ce.
Plecând de la premisa asta:
4 biți ar fi prea puțin, că n-ar încăpea toate caracterele latine (poți reprezenta maximum 16 numere)
16 biți ar fi prea mult și ar reprezenta risipă de resurse (iar în anii '70, memoria era ceva mai importantă decât este acum)
E o putere a lui 2 pentru ca se bazeaza pe porti on/off, ai sau n-ai tensiune pe fir. De ce 8 biti? Probabil pentru ca 2 si 4 erau prea putini ca sa cuprinda setul de caractere din alfabet. Cand au aparut cipurile, majoritatea aveau 16 pini, din care 2 sunt alimentare, 2 de control, 8 de date si restul… si ei pe acolo, de rezerva.
Parerea mea, fara sa citesc articolul.
I worked on the UIUC PLATO system in the 1970s : CDC-6600, 7600 cpus with 60-bit words. Back then everything used magnetic core memory and that memory was unbelievably expensive! Sewn together by women in southeast Asia, maybe $1 per word!
Having 6-bit bytes on a CDC was a terrific PITA! The byte size was a tradeoffs between saving MONEY (RAM) and the hassle of shift codes (070) used to get uppercase letters and rare symbols! Once semiconductor memory began to be available (2M words of ‘ECS’ - “extended core storage” - actually semiconductor memory - was added to our 1M byte memory in ~1978) computer architects could afford to burn the extra 2 bits in every word to make programming easier…
At about the same time microprocessors like the 8008 were starting to take off (1975). If the basic instruction could not support a 0-100 value it would be virtually useless! There was only 1 microprocessor that DID NOT use the 8-bit byte and that was the 12-bit intersil 6100 which copied the pdp-8 instruction set!
Also the invention of double precision floating point made 32-bit floating point okay. From the 40s till the 70s the most critical decision in computer architecture was the size of the floating point word: 36, 48, 52, 60 bits … But 32 is clearly inadequate. But the idea that you could have a second larger floating point fpu that handled 32 AND 64-bit words made 32-bit floating point acceptable…
Also in the early 1970s text processing took off, partly from the invention of ASCII (1963), partly from 8-bit microprocessors, partly from a little known OS whose fundamental idea was that characters should be the only unit of I/O (Unix -father of Linux).
So why do we have 8-bit bytes? Thank you, Gordon Moore!
Ei, n-au inventat cipurile ca sa construiasca computere. Intai au automatizat si ei ceva pe ici pe colo, o usa de garaj, un semafor… Apoi, daca tot au avut cipul au zis hai sa faca si un computer, de hobby.
