1. EET 252 Unit 3 Memory  Read Floyd, Chapter 10.  Study Unit 3 e-Lesson.  Do Lab #3.  Homework #3 and Lab #3 due next week.  Quiz next week.

2. Bit: The smallest unit of digital data, a single 1 or 0. Byte: A group of 8 bits. Nibble: A “half-byte”: a group of 4 bits. Word: Used in two ways: Sometimes means 2 bytes (or 16 bits). Sometimes means the data width that a particular chip or system uses: could be 4 bits, 8 bits, 16 bits, 32 bits, etc. Terms for Units of Data

3. Kilo-, Mega-, Giga- In engineering notation, Kilo means 1,000 (the same as 10 3 ) Mega means 1,000,000 (same as 10 6 ) Giga means 1,000,000,000 (same as 10 9 ) When talking about memories, theses terms have slightly different meanings: Kilo means 1,024 (the same as 2 10 ) Mega means 1,048,576 (same as 2 20 ) Giga means 1,073,741,824 (same as 2 30 )

4. Making Sense of Windows File Sizes Have you ever noticed that when you use Windows to look at a file’s size, it gives two numbers that don’t seem to match each other? Example: “Size on disk: 624 KB (638,976 bytes)” That’s because 624 x 1024 = 638,976. How many megabytes (MB) is in a file that contains 28,311,552 bytes?

5. © 2009 Pearson Education, Upper Saddle River, NJ 07458. All Rights ReservedFloyd, Digital Fundamentals, 10 th ed© 2009 Pearson Education, Upper Saddle River, NJ 07458. All Rights ReservedFloyd, Digital Fundamentals, 10 th ed The location of a unit of data in a memory is called the address. In personal computer memories, a byte is the smallest unit of data that can be addressed. Memory Units For example the blue byte is located in address 6.

6. A computer system has two primary busses: The data bus, which carries data and instructions from one part of the system to another. The address bus, which carries addresses of memory locations or external devices. These two busses may have the same width (number of bits), but they need not. When people talk about a “32-bit system” or a “64- bit system,” they’re talking about the width of the data bus. Computer Busses

7. © 2009 Pearson Education, Upper Saddle River, NJ 07458. All Rights ReservedFloyd, Digital Fundamentals, 10 th ed© 2009 Pearson Education, Upper Saddle River, NJ 07458. All Rights ReservedFloyd, Digital Fundamentals, 10 th ed Write Operations The two main memory operations are called read and write. A simplified write operation is shown in which new data overwrites the original data. Data moves to the memory. 1.The address is placed on the address bus. 2.Data is placed on the data bus. 3.A write command is issued. Address register Data register Address bus Address decoderByte organized memory array Write Data bus

8. © 2009 Pearson Education, Upper Saddle River, NJ 07458. All Rights ReservedFloyd, Digital Fundamentals, 10 th ed© 2009 Pearson Education, Upper Saddle River, NJ 07458. All Rights ReservedFloyd, Digital Fundamentals, 10 th ed Read Operations The read operation is actually a “copy” operation, as the original data is not changed. The data bus is a “two-way” path; data moves from the memory during a read operation. 1.The address is placed on the address bus. 2.A read command is issued. 3.A copy of the data is placed in the data bus and shifted into the data register. Address register Data register Address bus Address decoderByte organized memory array Read Data bus

9. Some Common Address Bus Widths The width (in bits) of an address bus determines the number of locations it can address: Width of Address BusNumber of locations 8 bits256 10 bits1 k 16 bits64 k 20 bits1 M 24 bits16 M 32 bits4 G

10. Powers of 2 (from Floyd, p. 809) This table answers the following questions: 2. What is the MOD of an n- bit counter? 3. How many addressable locations in a memory with n address pins? 1. How many rows are there in a truth table with n input variables?

11. A computer’s memory consists of many memory chips, which may be organized in different ways. Example: in the tiny memory below, each byte may be contained on a single chip, or may be spread across two or more chips. Computer Memory

12. The size and organization of a memory chip is given by a designation such as 16 x 4. The first number (16 in our example) tells how many addressable locations the chip contains. The second number (4 in our example) tells how many bits are contained in each of these addressable locations. Thus, an 8 x 8 chip, a 16 x 4 chip, and a 64 x 1 chip all have a bit capacity of 64 bits, but they’re organized differently. Designating a Memory Chip’s Size & Layout

13. We can tell how many address pins a memory chip needs by looking at the first number in its designation. For example, a 16 x 4 chip has 16 addressable locations. How many address pins are needed if we want to be able to select any one of these 16 locations? How many address pins would an 8 x 8 chip need? How many address pins would a 64 x 1 chip need? Address Input Pins

14. We can tell how many data output pins a memory chip needs by looking at the second number in its designation. For example, on a 16 x 4 chip, each location contains 4 bits, so to read out the contents of any location, we need 4 data output pins. How many data output pins would an 8 x 8 chip need? How many data output pins would a 64 x 1 chip need? Data Output Pins

15. Some memory chips are read-only memories (ROMs). These chips don’t have data input pins because you cannot change the contents of the memory locations. Other memory chips are read-write memories (confusingly called RAMs, for “random-access memory”). These may have data input pins that are separate from the data output pins, or the pins may be combined as data input/output (I/O) pins. Data Input Pins?

16. 7489 RAM (16 x 4) 6116 RAM (2048 x 8) TMS4700 ROM (1024 x 8) Some Memory Chip Datasheets

17. © 2009 Pearson Education, Upper Saddle River, NJ 07458. All Rights ReservedFloyd, Digital Fundamentals, 10 th ed© 2009 Pearson Education, Upper Saddle River, NJ 07458. All Rights ReservedFloyd, Digital Fundamentals, 10 th ed Memory Addressing In addition to the address bus and data bus, semiconductor memories have read and write control signals and chip select signals. Depending on the type of memory, other signals may be required. Chip Select (CS) or Chip Enable (CE) is used as part of address decoding. All other inputs are ignored if the Chip Select is not active. Read Enable (RE) and Write Enable (WE) signals are sent from the CPU to memory to control data transfer to or from memory. Output Enable (OE) is active during a read operation, otherwise it is inactive. It connects the memory to the data bus.

18. © 2009 Pearson Education, Upper Saddle River, NJ 07458. All Rights ReservedFloyd, Digital Fundamentals, 10 th ed© 2009 Pearson Education, Upper Saddle River, NJ 07458. All Rights ReservedFloyd, Digital Fundamentals, 10 th ed Memory Expansion Memory can be expanded in either word size or word capacity or both. To expand word size: Notice that the data bus size is larger, but the number of address is the same.

19. © 2009 Pearson Education, Upper Saddle River, NJ 07458. All Rights ReservedFloyd, Digital Fundamentals, 10 th ed© 2009 Pearson Education, Upper Saddle River, NJ 07458. All Rights ReservedFloyd, Digital Fundamentals, 10 th ed Memory Expansion To expand word capacity, you need to add an address line as shown in this example Notice that the data bus size does not change. What is the purpose of the inverter? Only one of the ICs is enabled at any time depending on the logic on the added address line.

20. A computer’s memory consists of many memory chips. Some of the bits on the address bus are used to select one of these chips (and to de-select all of the others). The remaining bits on the address bus are used to select a memory location within the selected chip…. Computer Memory

21. Example: Suppose a computer’s memory consists of 32 memory chips, each of which is 2048 x 8. How many bytes does the computer’s memory contain? How many bits are needed to select one of the 32 memory chips? Once a chip has been selected, how many bits are needed to select a memory location within that chip? How wide does this system’s address bus need to be? Computer Memory (Continued)

22. A computer system typically has one or more small, high-speed cache memories in addition to its large, slower main memory. Recently used data and instructions are temporarily stored in the cache memory so that if the processor needs them again, they can be retrieved more quickly than if they had to be retrieved from the main memory. See textbook’s Figure 10.15 (next slide). Cache Memory

23. Copyright ©2009 by Pearson Higher Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Digital Fundamentals, Tenth Edition Thomas L. Floyd Figure 10.15 Block diagram showing L1 and L2 cache memories in a computer system.

24. Most memory chips fall into one of the following three categories (which have many subcategories). 1.RAM (Random Access Memory) Read/write Volatile (Loses data when power is removed.) 2.ROM (Read-Only Memory) Impossible or difficult to write to Non-volatile 3.Flash memory Read/write Non-volatile Memory Technologies

25. © 2009 Pearson Education, Upper Saddle River, NJ 07458. All Rights ReservedFloyd, Digital Fundamentals, 10 th ed© 2009 Pearson Education, Upper Saddle River, NJ 07458. All Rights ReservedFloyd, Digital Fundamentals, 10 th ed RAM is for temporary data storage. It is read/write memory and can store data only when power is applied, hence it is volatile. Two major categories are static RAM (SRAM) and dynamic RAM (DRAM). The memory cells in SRAM are latches or flip-flops. The memory cells in Dynamic RAMs (DRAMs) are capacitors. Since the capacitors lose charge, they must be refreshed many times each second. Random Access Memory (RAM)

26. © 2009 Pearson Education, Upper Saddle River, NJ 07458. All Rights ReservedFloyd, Digital Fundamentals, 10 th ed Figure 10.7 The RAM family. Latch or flip-flop storage cell. Capacitor storage cell. Must be refreshed. High-density but slow. Used for main memory. Fast but low- density. Used for cache memory.

27. © 2009 Pearson Education, Upper Saddle River, NJ 07458. All Rights ReservedFloyd, Digital Fundamentals, 10 th ed© 2009 Pearson Education, Upper Saddle River, NJ 07458. All Rights ReservedFloyd, Digital Fundamentals, 10 th ed Read-Only Memory (ROM) Members of the ROM family are all considered non- volatile, because they retain data with power removed. Various members can be either permanent memory (truly read-only) or erasable (not truly read-only, but they are difficult to write to). ROMs are used to store data that is never (or rarely) changed, such as system initialization files.

28. © 2009 Pearson Education, Upper Saddle River, NJ 07458. All Rights ReservedFloyd, Digital Fundamentals, 10 th ed Figure 10.22 revised. The ROM family. Data written by the manufacturer, and can never be changed. Data written by the user, and can never be changed. Data written by the user, and can be changed with some difficulty.

29. © 2009 Pearson Education, Upper Saddle River, NJ 07458. All Rights ReservedFloyd, Digital Fundamentals, 10 th ed© 2009 Pearson Education, Upper Saddle River, NJ 07458. All Rights ReservedFloyd, Digital Fundamentals, 10 th ed Read-Only Memory (ROM) A ROM symbol is shown with typical inputs and outputs. The triangles on the outputs indicate it is a tri-stated device. To read a value from the ROM, an address is placed on the address bus, the chip is enabled, and a short time later (called the access time), data appears on the data bus. Address input lines A0A0 A1A1 A2A2 A3A3 A4A4 A5A5 A6A6 A7A7 E0E0 E1E1 O0O0 O1O1 O2O2 O3O3 Data output lines Address input lines Data outputs Address transition Data output transition tata Chip select Valid data on output lines Valid address on input lines

30. © 2009 Pearson Education, Upper Saddle River, NJ 07458. All Rights ReservedFloyd, Digital Fundamentals, 10 th ed© 2009 Pearson Education, Upper Saddle River, NJ 07458. All Rights ReservedFloyd, Digital Fundamentals, 10 th ed PROMs, UV EPROMs and EEPROMs PROMs are programmable ROM, in which a fused link is burned open during the programming process. Once the PROM is programmed, it cannot be reversed. A UV EPROM can be erased by exposure to UV light through a window. To program it, a high voltage is applied to V PP and OE is brought LOW. O0O0 O1O1 O2O2 O3O3 O4O4 O5O5 O6O6 O7O7 A0A0 A1A1 A2A2 A3A3 A4A4 A5A5 A6A6 A7A7 A8A8 A9A9 A 10 CE/PGM OE V PP Another type of erasable PROM is the EEPROM, which can be erased and programmed with electrical pulses.

31. Copyright ©2009 by Pearson Higher Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Digital Fundamentals, Tenth Edition Thomas L. Floyd Figure 10.29 MOS PROM array with fusible links. (All drains are commonly connected to V DD.)

32. © 2009 Pearson Education, Upper Saddle River, NJ 07458. All Rights ReservedFloyd, Digital Fundamentals, 10 th ed© 2009 Pearson Education, Upper Saddle River, NJ 07458. All Rights ReservedFloyd, Digital Fundamentals, 10 th ed Flash Memory Flash memories are high density read/write memories that are nonvolatile. They have the ability to retain charge for years with no applied power. Flash memory uses a MOS transistor with a floating gate as the basic storage cell. The floating gate can store charge (logic 0) when a positive voltage is applied to the control gate. With little or no charge, the cell stores a logic 1. logic 0 is storedlogic 1 is stored

33. © 2009 Pearson Education, Upper Saddle River, NJ 07458. All Rights ReservedFloyd, Digital Fundamentals, 10 th ed© 2009 Pearson Education, Upper Saddle River, NJ 07458. All Rights ReservedFloyd, Digital Fundamentals, 10 th ed FIFO Memory FIFO means first in-first out. This type of memory is basically an arrangement of shift registers. It is used in applications where two systems communicate at different rates.

34. © 2009 Pearson Education, Upper Saddle River, NJ 07458. All Rights ReservedFloyd, Digital Fundamentals, 10 th ed© 2009 Pearson Education, Upper Saddle River, NJ 07458. All Rights ReservedFloyd, Digital Fundamentals, 10 th ed LIFO Memory LIFO means last in-first out. In microprocessors, a portion of RAM is devoted to this type of memory, which is called the stack. Stacks are very useful for temporary storage of internal registers, so that the processor can be interrupted but can easily return to a given task. A special register, called the stack pointer, keeps track of the location that data was last stored on the stack. This will be the next data to be taken from the stack when needed. Top-of-stack Stack pointer

35. “Memory” refers to semiconductor devices of the kinds we’ve been discussing (RAM, ROM, Flash). “Storage” refers to non-semiconductor non-volatile devices used to store huge quantities of data. Major categories include: Magnetic disk (such as computer hard drives) Magnetic tape Optical disk (CDs and DVDs) Memory versus Storage

36. © 2009 Pearson Education, Upper Saddle River, NJ 07458. All Rights ReservedFloyd, Digital Fundamentals, 10 th ed© 2009 Pearson Education, Upper Saddle River, NJ 07458. All Rights ReservedFloyd, Digital Fundamentals, 10 th ed Magnetic Hard Drive The magnetic hard drive is the backbone of computer mass storage and is applied to other devices such as digital video recorders. Capacities of hard drives have increased exponentially, with 1 TB (1 trillion bytes!) drives available today. Hard drive with cover removed

37. © 2009 Pearson Education, Upper Saddle River, NJ 07458. All Rights ReservedFloyd, Digital Fundamentals, 10 th ed© 2009 Pearson Education, Upper Saddle River, NJ 07458. All Rights ReservedFloyd, Digital Fundamentals, 10 th ed Optical Storage The compact disk (CD) uses a laser to burn tiny pits into the media. Surrounding the pits are flat areas called lands. The CD can be read using a low-power IR laser that detects the difference between pits and lands. Binary data is encoded with a special method called negative non-return to zero encoding. A change from a pit to a land or a land to a pit represents a binary one, whereas no change represents a zero. A standard 120 mm CD can hold approximately 700 MB of data.