CHAPTER 4 - The Memory System and Hierarchy

Location

internal, external. (key characteristic of computer memory systems)

Capacity

number of words, number of bytes (key characteristic of computer memory systems)

Unit of transfer

word, block (key characteristic of computer memory systems)

Access method

sequential, direct, random, associative (key characteristic of computer memory systems)

Performance

access time, cycle time, transfer rate (key characteristic of computer memory systems)

Physical type

semiconductor, magnetic, optical, magneto-optical (key characteristic of computer memory systems)

Physical characteristics

vlatile/non-volatile, erasable/non-erasable (key characteristic of computer memory systems)

Organization

memory modules (key characteristic of computer memory systems)

Transfer rate

Where

Tn - Average time to read or write n bits

TA - Average access time

n - Number of bits

R - Transfer rate, in bits per second (bps)

Greater

Faster access time, _______ cost per bit

Smaller

Greater capacity, _______ cost per bit

Slower

Greater capacity, ______ access time.

Cache memory

is designed to combine the memory access time of expensive, high- speed memory with the large memory size of less expensive, lower-speed memory.

memory cell

The basic element of semiconductor memory is the ______ ____

semiconductor

_____________ memory cells share certain properties

-They exhibit two stable (or semi-stable) states

-They are capable of being written

-They are capable of being read

DRAM

is made with cells that store data as charge on capacitors. The presence or absence of charge in a capacitor is interpreted as a binary 1 or 0. Because capacitors have a natural tendency to discharge, dynamic RAMs require periodic charge refreshing to maintain data storage. It has a tendency of the stored charge to leak away, even with power continuously applied.

SRAM

is a digital device that uses the same logic elements used in the processor. binary values are stored using traditional flip-flop logic-gate configurations. it will hold its data as long as power is supplied to it.

SRAM

is used for cache memory (both on and off chip)

DRAM

is used for main memory.

ROM

contains a permanent pattern of data that cannot be changed. Nonvolatile. no power source is required to maintain the bit values in memory

Microprogramming

important application of ROMs is ________________. Other potential applications include Library subroutines, System programs, and Function tables

ROM

The data insertion step includes a relatively large fixed cost, whether one or thousands of copies of a particular ___ are fabricated.

ROM

There is no room for error. If one bit is wrong, the whole batch of ___s must be thrown out.

programmable ROM

(PROM)

PROM

type of rom. nonvolatile and may be written into only once

read-mostly memory

type of rom. useful for applications in which read operations are far more frequent than write operations

erasable programmable read-only memory

(EPROM)

EPROM

type of rom. read and written electrically

electrically erasable programmable read-only memory

(EEPROM)

EEPROM

type of rom. a read-mostly memory that can be written into at any time without erasing prior contents

flash memory

type of rom. form of semiconductor memory. gets its name because the microchip is organized so that a section of memory cells are erased in a single action or "flash."

Synchronous DRAM

exchanges data with the processor synchronized to an external clock signal and running at the full speed of the processor/memory bus without imposing wait states.

DDR SDRAM

provides several features that dramatically increase the data rate. developed by the JEDEC Solid State Technology Association. achieves higher data rates in three ways

-the data transfer is synchronized

-DDR uses higher clock rate on the bus

-a buffering scheme is used

JEDEC Solid State Technology Association

who developed DDR SDRAM?

Double Data Rate Synchronous Dynamic RAM

DDR SDRAM

flash memory

introduced in the mid-1980s. intermediate between EPROM and EEPROM. uses an electrical erasing technology, can be erased in one or a few seconds

Mid-1980s

flash memory was introduced in the ___-____s. intermediate between EPROM and EEPROM. uses an electrical erasing technology, can be erased in one or a few seconds