Page 1
11/5/2003 Other Memories 1
Other memories
• Last time we showed how to build arbitrarily-large static memories
from single-bit RAM cells.
• Today we’ll look at some other kinds of memories.
– Dynamic RAM is used for the bulk of computer memory.
– Read-only memories and PLAs are two “programmable logic devices,”
which can be considered as special types of memories.
Page 2
11/5/2003 Other Memories 1
Other memories
• Last time we showed how to build arbitrarily-large static memories
from single-bit RAM cells.
• Today we’ll look at some other kinds of memories.
– Dynamic RAM is used for the bulk of computer memory.
– Read-only memories and PLAs are two “programmable logic devices,”
which can be considered as special types of memories.
11/5/2003 Other Memories 2
Dynamic memory in a nutshell
• Dynamic memory is built with capacitors.
– A stored charge on the capacitor represents a logical 1.
– No charge represents a logic 0.
• However, capacitors lose their charge after a few milliseconds. The
memory requires constant refreshing to recharge the capacitors.
(That’s what’s “dynamic” about it.)
• Dynamic RAMs tend to be physically smaller than static RAMs.
– A single bit of data can be stored with just one capacitor and one
transistor, while static RAM cells typically require 4-6 transistors.
– This means dynamic RAM is cheaper and denser—more bits can be
stored in the same physical area.
Page 3
11/5/2003 Other Memories 1
Other memories
• Last time we showed how to build arbitrarily-large static memories
from single-bit RAM cells.
• Today we’ll look at some other kinds of memories.
– Dynamic RAM is used for the bulk of computer memory.
– Read-only memories and PLAs are two “programmable logic devices,”
which can be considered as special types of memories.
11/5/2003 Other Memories 2
Dynamic memory in a nutshell
• Dynamic memory is built with capacitors.
– A stored charge on the capacitor represents a logical 1.
– No charge represents a logic 0.
• However, capacitors lose their charge after a few milliseconds. The
memory requires constant refreshing to recharge the capacitors.
(That’s what’s “dynamic” about it.)
• Dynamic RAMs tend to be physically smaller than static RAMs.
– A single bit of data can be stored with just one capacitor and one
transistor, while static RAM cells typically require 4-6 transistors.
– This means dynamic RAM is cheaper and denser—more bits can be
stored in the same physical area.
11/5/2003 Other Memories 3
SDRAM
• Synchronous DRAM, or SDRAM, is one of
the most common types of PC memory now.
• Memory chips are organized into “modules”
that are connected to the CPU via a 64-bit
(8-byte) bus.
• Speeds are rated in megahertz: PC66, PC100
and PC133 memory run at 66MHz, 100MHz
and 133MHz respectively.
• The memory bandwidth can be computed by
multiplying the number of transfers per
second by the size of each transfer.
– PC100 can transfer up to 800MB per
second (100MHz x 8 bytes/cycle).
– PC133 can get over 1 GB per second.
(from amazon.com)
Page 4
11/5/2003 Other Memories 1
Other memories
• Last time we showed how to build arbitrarily-large static memories
from single-bit RAM cells.
• Today we’ll look at some other kinds of memories.
– Dynamic RAM is used for the bulk of computer memory.
– Read-only memories and PLAs are two “programmable logic devices,”
which can be considered as special types of memories.
11/5/2003 Other Memories 2
Dynamic memory in a nutshell
• Dynamic memory is built with capacitors.
– A stored charge on the capacitor represents a logical 1.
– No charge represents a logic 0.
• However, capacitors lose their charge after a few milliseconds. The
memory requires constant refreshing to recharge the capacitors.
(That’s what’s “dynamic” about it.)
• Dynamic RAMs tend to be physically smaller than static RAMs.
– A single bit of data can be stored with just one capacitor and one
transistor, while static RAM cells typically require 4-6 transistors.
– This means dynamic RAM is cheaper and denser—more bits can be
stored in the same physical area.
11/5/2003 Other Memories 3
SDRAM
• Synchronous DRAM, or SDRAM, is one of
the most common types of PC memory now.
• Memory chips are organized into “modules”
that are connected to the CPU via a 64-bit
(8-byte) bus.
• Speeds are rated in megahertz: PC66, PC100
and PC133 memory run at 66MHz, 100MHz
and 133MHz respectively.
• The memory bandwidth can be computed by
multiplying the number of transfers per
second by the size of each transfer.
– PC100 can transfer up to 800MB per
second (100MHz x 8 bytes/cycle).
– PC133 can get over 1 GB per second.
(from amazon.com)
11/5/2003 Other Memories 4
DDR-RAM
• A newer type of memory is Double Data Rate, or DDR-RAM.
• It’s very similar to regular SDRAM, except data can be transferred on
both the positive and negative clock edges. For 100-133MHz buses, the
effective memory speeds appear to be 200-266MHz.
• This memory is confusingly called PC1600 and PC2100 RAM, because
– 200MHz x 8 bytes/cycle = 1600MB/s
– 266MHz x 8 bytes/cycle = 2100MB/s.
• DDR-RAM has lower power consumption, using 2.5V instead of 3.3V like
SDRAM. This makes it good for notebooks and other mobile devices.
Page 5
11/5/2003 Other Memories 1
Other memories
• Last time we showed how to build arbitrarily-large static memories
from single-bit RAM cells.
• Today we’ll look at some other kinds of memories.
– Dynamic RAM is used for the bulk of computer memory.
– Read-only memories and PLAs are two “programmable logic devices,”
which can be considered as special types of memories.
11/5/2003 Other Memories 2
Dynamic memory in a nutshell
• Dynamic memory is built with capacitors.
– A stored charge on the capacitor represents a logical 1.
– No charge represents a logic 0.
• However, capacitors lose their charge after a few milliseconds. The
memory requires constant refreshing to recharge the capacitors.
(That’s what’s “dynamic” about it.)
• Dynamic RAMs tend to be physically smaller than static RAMs.
– A single bit of data can be stored with just one capacitor and one
transistor, while static RAM cells typically require 4-6 transistors.
– This means dynamic RAM is cheaper and denser—more bits can be
stored in the same physical area.
11/5/2003 Other Memories 3
SDRAM
• Synchronous DRAM, or SDRAM, is one of
the most common types of PC memory now.
• Memory chips are organized into “modules”
that are connected to the CPU via a 64-bit
(8-byte) bus.
• Speeds are rated in megahertz: PC66, PC100
and PC133 memory run at 66MHz, 100MHz
and 133MHz respectively.
• The memory bandwidth can be computed by
multiplying the number of transfers per
second by the size of each transfer.
– PC100 can transfer up to 800MB per
second (100MHz x 8 bytes/cycle).
– PC133 can get over 1 GB per second.
(from amazon.com)
11/5/2003 Other Memories 4
DDR-RAM
• A newer type of memory is Double Data Rate, or DDR-RAM.
• It’s very similar to regular SDRAM, except data can be transferred on
both the positive and negative clock edges. For 100-133MHz buses, the
effective memory speeds appear to be 200-266MHz.
• This memory is confusingly called PC1600 and PC2100 RAM, because
– 200MHz x 8 bytes/cycle = 1600MB/s
– 266MHz x 8 bytes/cycle = 2100MB/s.
• DDR-RAM has lower power consumption, using 2.5V instead of 3.3V like
SDRAM. This makes it good for notebooks and other mobile devices.
11/5/2003 Other Memories 5
RDRAM
• Another new type of memory called RDRAM
is used in the Playstation 2 as well as some
Pentium 4 computers.
• The data bus is only 16 bits wide.
• But the memory runs at 400MHz, and data
can be transferred on both the positive and
negative clock edges.
– That works out to a maximum transfer
rate of 1.6GB per second.
– You can also implement two “channels”
of memory, resulting in up to 3.2GB/s of
bandwidth.
(from amazon.com)
Read More