Other Memories - PPT, Computer Science Engineering, Semester Notes | EduRev

 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)