mmaxim@sc9.intel.com (Michael A. Maxim) (05/29/91)
Hello people;
I noticed some concern and confusion about E/EEPROMS on the Virus-l
list lately, and, since I work at Intel's NVM development fab, I
figured the least I could do was to clear things up a bit. Some of
this is pretty pedestrian stuff, so you can skip to the end if you
want...
Definitions/explanations:
NVMs - Non-Volatile Memories. ROMS, PROMS,EPROMS,EEPROMS, ferromagnetic
DRAM's, etc. Memory storage devices that don't lose data when the
power goes out.
fab - Short for Fabrication. Place where silicon wafers are turned into
semiconductor devices. Very clean, very very expensive factory.
ROMs - Also called mask ROMs. Read Only Memories. Programming is done
during manufacture. "Cheapest" memory for high volume use on static
designs. Minimum order might be several-to-tens of thousand parts.
Real peanut parts, these may only cost pennies apiece.
PROM - Programmable Read Only Memory. These babies you program once.
Heard the term "burn in a PROM"? Very literal saying. To program
them, you actually fuse the innards into the configuration you want.
Inexpensive unless you make lots of mistakes, 'cause they are either
right or they are scrap.
EPROM - Also called UV EPROM's. Invented by Intel 'way back inna '70's. An
Erasable Programmable Read Only Memory. They are programmed
electronically, and erased with ultraviolet light. They've got a
little transparent window in the package just for that purpose (it's
usually covered up with a sticker or something, though; even
ambient light WILL eventually wipe them out...note also that if the
package doesn't have a window then your EPROM is effectively a PROM.
Lots of these are used in automobile engine controllers, bios chips,
etc. Also pretty cheap, available commercially in densities up to
4mbit or so.
EEPROM - Also called E2PROMS. These are Electronically Erasable Programmable
Read Only Memories. You don't need UV to erase them. However, you
do generally need at least 11 volts on one of the pins to erase/
program them. More on this later. More expensive than EPROMS, but
still cheap in all but the largest sizes. Should replace EPROMs in
most applications in the next few years, and may even take a big
chunk out of the disk drive and DRAM markets.
Flash - The hot rods of EEPROMs, also invented by Intel (of course. ~8^) )
They program and erase quickly and have fast access times. These are
available in either bulk (entire bank or chip) or sector (single byte)
erase versions. Their lifetime is measured in program/erase cycles.
Some parts have lifetimes as low as 1000 erase/program cycles; these
are useful for some applications that don't require many changes, but
aren't any good for solid state disks or memory cards, for example.
Other types have program/erase lifetimes of 100K+ cycles. (guess who
makes those... ~8^) ) Right now there are many different
manufacturers who make or plan to make Flash E2PROMS, including the
market leader Intel, AMD, Seeq Technologies, Atmel, NEC, Hitachi,
Toshiba, Oki, Mitsubishi, and maybe a couple others I missed.
Here's a shameless plug for the company that signs my paychecks, and
what seems to have caused the concern in the virus community.
Intel has just recently introduced the 1mbit 28F001BX Flash. It's
designed for use in PC operating system software and embedded control
applications. Features include a security-protected 8kb block on the
chip to boot applications, 2 4kb parameter blocks for configuration
info, a 112kb main memory block, 150 ns access time and single byte
erase. It's available in PDIP or PLCC (plastic dual inline package or
plastic leaded chip carrier, I think...I just do wafers, not
packaging) and costs $17.20 in quantities of 1000. What does
security-protected mean? Good question. I'll see if I can find out.
Here's my own $.02: unless a really clever virus finds a way to shove
a sun lamp into your PC, you have nothing to worry about with EPROMs.
As for EEPROMs and Flash chips, they look just like PROMs or EPROMs to
your system. Unless your system is specially configured to reprogram
them (remember that pin I mentioned earlier?) there is nothing ANY
program could do to change an EEPROM. If some board maker actually
wanted to enable software modification to the BIOS EEPROM, there is no
reason that he couldn't do it; but that is a problem with the board
and manufacturer, not the chips.
Sorry so long winded.
M2.
`-_-'
'U` Have a day.
DisClaimEr: I think most of the stuff above is pretty near correct,
and of course I don't speak for Intel in any official or unofficial
way. I also didn't have anything to do with the 28F001BX, but it does
sound like a neat chip.
++===========================++=============================================++
|| Michael A. Maxim || ||
|| Intel California TD || "If all else fails, immortality can always||
|| D2 Thin Films || be assured by spectacular error" ||
|| 408/765-9435 || -John Kenneth ||
|| MMAXIM%SC9@SC.INTEL.COM || Galbraith ||
++===========================++=============================================++