Page 194 - Bebop to The Boolean Boogie An Unconventional Guide to Electronics Fundamentals, Components, and Processes
P. 194
MemoryICs 175
EEPROMs
A further technology called -bits wide (although dual configurations
electrically -erasable read-only memory have been used to provide 128 bit wide
(EEPROM or E2PROM) l9 was busses in really high-end computers).
developed towards the end of the Thus, assuming a standard 64-bit
wide PClOO (100 MHz) memory
1970s. E2PROMs are electrically
, the peak data throughput will be
programmable by the designer and x 100 = 800 megabytes per second. If a
are nonvolatile, but can be electri- DR version becomes available as discussed
cally erased and reprogrammed rlier, this would rise to 1,600 megabytes
should the designer so desire. per second. Furthermore, a 128-bit wide
Additionally, by means of addi- DDR (using dual 64-bit modules in parallel)
ould have a peak bandwidth of 3,200
tional circuitry, an E2PROM can megabytes per second.
be erased and reprogrammed while Towards the end of the 199Os, an
remaining resident on the circuit rnative memory concept called Rambus
board, in which case it may be an to gain attention (as usual this is
referred to as in-system progrummable based on core DRAM concepts presented
(ISP). a cunning manner). By around 2000,
rsonal computers equipped with memory
An EPROM cell is based on a modules formed from Rambus DRAM
single transistor and is therefore (RDRAM) devices were available. These
very efficient in terms of silicon memory modules were 16-bits (2-bytes)
real estate, while an equivalent ide, and were accessed on both edges of
E2PROM cell is based on two a 400 MHz clock, thereby providing a peak
ata throughput of 2 x 2 x 400 = 1,600
transistors and requires more area megabytes per second. (Just to be confus-
on the silicon. However, an ing, these devices are actually referenced as
EPROM device must be erased and 00 MHz Rambus DRAM,“ but this is just
reprogrammed in its entirety, while arketing spin trying to make using both
an E2PROM device can be erased s of a 400 MHz clock sound more
and reprogrammed on a word-by-
word basis.
bus using both edges of a 533 MHz clock
(the official announcements quote ”1,066
MHz Rambus DRAM,” but this is the same
19 In conversation, some people pronounce marketing spin as noted above). Whatever,
EEPROM as ”E-E-PROM” (spelling out this will provide a peak bandwidth of 4,200
“E-E followed with “prom”), while megabytes per second.
others say “E-squared-prom.”
