[Info-vax] OT? BIOS is NOR because (a) word addressable (b) NOR needs no ECC.

[Neil Rieck]

On Aug 18, 7:07 pm, John Wallace <johnwalla... at yahoo.co.uk> wrote:
> On Aug 18, 11:33 pm, Neil Rieck <n.ri... at sympatico.ca> wrote:
>
[...snip...]
>
> BIOS chips and the like are NOR based because NOR is word addressable
> and can thus be treated like a traditional ROM (I go back to 2704
> UVEPROM, thank you). With a NOR flash chip, code can in principle be
> executed directly from the memory (see "execute in place"). You simply
> can't do that transparently with block-at-a-time-transfer NAND flash.
> NAND flash's block addressable nature also has the consequence that
> some transistor-level failures are tolerable because there will be ECC
> going on at some level somewhere. Failures being tolerable makes it
> cheaper.- Hide quoted text -
>
> - Show quoted text -

You are correct. NAND-based flash is smaller and cheaper, but must be
written (and read?) a block at a time. NOR-based flash provides total
random access to individual bytes which makes it more like early RAM
or ROM.

BTW, I only go back to the 2708 EPROM

:-)

Neil