Feb 2, 2011 ... FLASH memory - a type of PROM that can be easily altered by the ... (flashed)
without having to take them out of the computer, and without.
2/17/16
Memory Overview Curtis Nelson Walla Walla University
Overview - Memory Types n n
n
Magnetic tape (used primarily for long term archive) Magnetic disk n Hard disk (File, Directory, Folder) n Floppy disks n Zip disks Optical media n CD (680 MB) n DVD (4.7 GB) n Magneto-optical disks
• Semiconductor Memory – Read Only Memory - ROM • Permanent and non-volatile • Can only be read – Random Access Memory - RAM • Temporary and volatile • Can be read or written
1
2/17/16
Storage Capacity • The amount of memory available is measured in bytes
Name
Abbreviation
Approx. # of Bytes
Exact # of Bytes
Approx. Pages of Text
Byte
B
One
1
One character
Kilobyte
KB (or K)
One thousand
1,024
One-half page
Megabyte
MB
One million
1,048,576
500 pages
Gigabyte
GB
One billion
1,073,741,824
500,000 pages
Terabyte
TB
One trillion
1,099,511,627,776
500,000,000 pages
Magnetic Hard Disk Drives
2
2/17/16
Semiconductor - Read Only Memories • Data is programmed into the chip using an external programmer • The programmed chip is used as a component in the circuit • The circuit doesn’t change the contents of the ROM • When power is removed from a ROM chip, the information is not lost, so it is a nonvolatile type of memory • ROM’s can typically be written once, but read many times. One such use is to store the BIOS (Basic Input/Output System) for a PC external to the microprocessor • The contents of the ROM are hard wired by the manufacturer in a typical ROM chip. When you turn the computer on, ROM automatically prepares the computer system and loads the initial display screen prompt
ROM Types • Masked ROM – programmed with its data when the chip is fabricated • PROM – ROM that is programmable by the user using a standard PROM programmer, by burning some special type of fuses. Once programmed, is not possible to program again • EPROM – erasable ROM; the chip can be erased and reprogrammed; programmed at higher voltages (~25 volts); erased by UV light • EEPROM – Electrically Erasable PROM; possible to modify individual locations, leaving others unchanged; one common use of the EEPROM is in BIOS of personal computers • FLASH memory - a type of PROM that can be easily altered by the user. They are also called EEPROMs (Electrically Erasable Read Only Memory) because they can be electrically erased then written on to (flashed) without having to take them out of the computer, and without using ultraviolet light. • Since RAM can be read faster than most ROMs, the frequently used content of the ROM is sometimes copied to RAM (shadowed)
3
2/17/16
Random Access Memory - RAM • • • • • • •
Usually referred to as Main Memory A collection of cells Each cell has an address and a value Cells can be accessed randomly (so can ROM) RAM is volatile All data is stored in binary format Bit, byte, and word are the units of data
RAM - Continued • Applications are typically loaded from slower storage (hard drives) into RAM during computer use • Data pins on a RAM chip are bidirectional (data can flow into or out of the chip via these pins), as opposed to those of ROM that are output only • A RAM has a directional select signal R/W’; When R/W’=1, the chip outputs data to the rest of the circuit; when R/W’ = 0 it inputs data from the rest of the circuit
4
2/17/16
RAM - Continued • RAM chips are typically packaged on small circuit boards called memory modules, which are inserted into special slots on the motherboard. • DIMMs, or dual inline memory modules provide a 64-bit data path to the processor. Older SIMMs only provide a 32-bit path. • The amount of RAM needed depends on the types of applications you intend to run on the computer. Software programs indicate the minimum amount of RAM required to run. How much RAM determines how many programs and how much data your computer can handle at one time.
Topic not covered: The Cache
RAM Types n n n n
•
SRAM (static) DRAM (dynamic) EDO RAM (extended data out) SDRAM (synchronous dynamic - most new PC’s are equipped with this RAM which is able to synchronize itself with the processor, enabling data transfer at more than twice the speed of previous RAM technologies) Class - ???
5
2/17/16
Static RAM • Static RAM (SRAM) – is more like a register; once the data has been written, it will stay valid, it doesn’t have to be refreshed. Static RAM is faster than DRAM, also more expensive • Memory cell: consists of 4-6 transistors and cross coupled inverters • Large cell • Loses data when power disconnected
0
0
O
D
1
1 W
Static RAM – Cache Memories
•
Cache Memories are small, fast static RAM memory that improves CPU’s efficiency. Caches increase computer throughput, and are a high-speed holding area for program instructions and data. Caches hold only instructions and data that are likely to be needed soon by the CPU. While programs are running on the computer, the same data or instructions might be needed frequently. In such cases, the processor first checks the cache memory for the data or instructions, thereby reducing the need for frequent access to the RAM and speeding up the processing
6
2/17/16
MIPS Processor
Dynamic RAM • Dynamic RAM (DRAM) – are like leaky capacitors. Initially, data is stored in the DRAM chip, charging its memory cells to maximum values. The charge slowly leaks out and eventually would go to zero. Before this happens, a refresh circuit reads the contents of the DRAM and rewrites the data to its original locations, thus restoring the memory cells to their maximum charges
7
2/17/16
First 1,024 Bit Memory Chip -- 1970 Intel Corporation DRAM • 1970’s processes usually had only nMOS transistors – Inexpensive, but consume power while idle • 1980s-present: CMOS processes for low idle power
VLSI Design
15
First 256-Bit Static RAM -- 1970 The Fairchild 4100
VLSI Design
16
8
2/17/16
New Image Sensing Method -- 1970 First 8-bit Charge-Coupled Device Bell Laboratories
VLSI Design
17
First EPROM -- 1971
The INTEL 1702
VLSI Design
18
9
2/17/16
First 65,536 Bit Dynamic Memory Chip -1977 IBM Corporation
VLSI Design
19
First 294,912 Bit Dynamic RAM Memory -1981 IBM Corporation
VLSI Design
20
10
2/17/16
Memory Organization • A memory chip of size 512 X 8 has 512 memory locations, each of which has 8 bits • The address input of a memory chip chooses one of its locations. A memory chip with 2 n locations requires n address inputs, usually labeled An-1An-2 … A0 (512 X 8 memory has address lines A8A7A6 … A0) • The data pins on a memory chip are used to access the data. There is one pin per bit in each location. For chips with m bits per location, these pins are Dm-1Dm-2 … D0 (512 X 8 memory has data lines D7D6D5 … D0) • Other pins – Chip enable (CE) and Output Enable (OE) enable or disable the chip data outputs. When disabled, the data pins output a high impedance state (Z); CE may be active high or low – R/W indicates whether a read or write operation is being performed
Ram Inputs/Outputs • • • • • •
Im-1..I0: input port An-1…A0: address lines CS: chip select; i.e. enable RWS: read/write select Om-1…O0: output port I/O ports are usually combined
11
2/17/16
Memory Systems Organization • Two or more memory chips can be combined to create memory with more bits per location (two 8X2 chips can create an 8X4 memory)
Memory Systems Organization • Two or more memory chips can be combined to create more locations (two 8X2 chips can create 16X2 memory)
12
2/17/16
Summary • • • • •
Semiconductor memory comes in many flavors RAM and ROM are the two main families RAM is composed of Static and Dynamic types Both are volatile, static is faster, dynamic is more dense Memory technology is what drives advances in IC process technology
13
