Untitled Quiz

Introduction

• This document presents study notes for computer architecture and microprocessors.

Memory

• Memory is a storage location for data.
• Organized into individual cells.
• Each cell has a unique size (in bits).
• Each cell has a unique address. The address allows identifying the location to store information.
• Number of bits to represent an address is finite and predetermined.
• Different systems may have different values.

Memory Description

• Memory is described using two independent pieces of information:
• The number of possible addresses.
• The size of the words in the memory.
• The total size of the memory represents the total number of bits that can be stored in the memory. Calculated as:
  • total memory size = number of addresses * size of a word

Memory Capacity Calculation

• Memory size is calculated using the formula:
  • Memory size = number of addresses * size of a word
• Example:
  • 256 addresses x 1 byte (8 bits) = 256 bytes

Questions & Answers

• Question 1: A memory stores 8-bit words (1 byte) and has 2^16 addresses. What is the total memory size in kilobytes?
• Answer: 64 KB
• Question 2: A memory uses 16-bit words (2 bytes) and requires 8 bits for addressing. What is the total memory size in bytes?
• Answer: 512 bytes
• Question 3: A memory has a total size of 32 MB and uses 32-bit words. How many bits are needed for addressing?
• Answer: 23 bits

Memory Characteristics

• Capacity: The total number of bits a memory can hold. Usually expressed in bytes.
• Access Time: The time it takes to read or write data.
• Memory Cycle: The minimum time between two consecutive memory accesses.
• Volatility: Whether the memory retains data when power is off (volatile) or not (non-volatile).

Memory Access Methods

• Sequential access: Data is accessed sequentially. It's slow.
• Direct access: Each piece of information has a unique address. Accessing is fast. Example: main memory
• Associative access: Information is identified by a key (or tag). Fast access. Example: cache memory

Memory Hierarchy

• The ideal is to use a fast memory with high capacity.
• Problem: large capacity memories are often very slow, and fast memories are expensive.
• To achieve a good balance of cost and performance, a memory hierarchy is used (multiple levels of memory).
• Faster memories (caches and registers) hold the most frequently used information. Slower, but larger memories (main memory and mass storage) store less-frequently accessed information.

Registers

• Fastest memory elements.
• Located in the processor.
• Used for storing intermediate results and operands.
• Small capacity.

Cache Memory

• Intermediate memory between the processor and main memory.
• Significantly faster access times than main memory (4 to 20 times faster).
• Small capacity.
• Used for storing frequently accessed data.

Types of Memory (Summary)

• Volatile: loses data when power is off.
• Non-volatile: data is retained when power is off.
• Static memory (SRAM): doesn't need refreshing; usually cache. High cost but fast access times.
• Dynamic memory (DRAM): needs periodic refreshing; typically main memory in computers; less expensive but slower than SRAM

ROM (Read-Only Memory):

• Non-volatile memory.
• Data is permanently stored during manufacturing.
• Used primarily for firmware, not directly changeable by users.

PROM:

• Programmable Read-Only Memory.
• Designed for programming once by the user.
• Non-volatile memory.

EPROM:

• Erasable Programmable Read-Only Memory.
• Can be erased and reprogrammed using UV light.
• Non-volatile memory

EEPROM (Electrically Erasable Programmable ROM):

• Programmable and erasable electrically, no need for UV light.
• Often used for storing small amounts of configuration information.
• Non-volatile memory.

FLASH:

• Similar to EEPROM for storage capacity but electrically erasable, unlike EEPROM.
• Increasingly for storage devices (flash drives, SSDs).
• Non-volatile memory

DRAM (Dynamic RAM)

• Common type of RAM.
• Needs refreshing.
• Larger capacities at a lower cost than SRAM (for main memory).

SRAM (Static RAM)

• High speed with high cost versus DRAM.
• No need for refreshing.
• Usually used as cache.

Buses

• Buses are groups of electrical lines connecting different components.
• They allow communication between these parts.
• Different types each for specific tasks:
  • Address Bus: to select the location to read from or write into
  • Data Bus: actually carries the data to read or write
  • Control Bus: for controlling the flow of data on the data bus (write or read?)

Memory Operations (Reading/Writing)

• CPU initiates all actions.
• Reading: The CPU puts the address required on the address bus. The memory then sends to the CPU the data from the specified physical location on the data bus.
• Writing: The CPU puts the address to store the data on the address bus, the data to store on the data bus, and signals the memory to write on the control bus.

Exercises and Solutions

• Detailed exercise questions and their solutions are provided for better understanding. These exercises often involve memory type, capacity calculations, address ranges calculation, and memory access principles.