Sequential Systems and Computer Memory Essentials

Sequential Systems Design

A systematic way of designing any machine that passes through different states. Examples include counters, traffic lights, and vending machines. Generally called Finite State Machines/Automatas.

Mealy Machine

Outputs are a function of both inputs and the current state.

Moore Machine

Outputs are a function of the current state only.

Computer Memory

Part of the computer that stores information: instructions and data.

Organization:

Address: Identifies memory position

Content: Stored information

Memory Cell

Minimum storing element: one bit.

Word

Group of bits implied in each memory operation (8, 16, 32, 64, ... bits). It defines data bus size.

Basic Operations

Read (R) and Write (W)

Capacity

Maximum quantity of information that a memory system can store. Usual measures:

• Kilobyte (KB) = 2¹⁰ bytes
• Megabyte (MB) = 2¹⁰ KB = 2²⁰ bytes
• Gigabyte (GB) = 2¹⁰ MB = 2³⁰ bytes
• Terabyte (TB) = 2¹⁰ GB = 2⁴⁰ bytes

Velocity, Access Time

Elapsed time since the moment a memory address is provided until the data contained in it is accessible.

Memory Cycle

Elapsed time between two consecutive memory accesses.

Bit Cost

Total memory cost divided by its capacity in bits.

Memory Hierarchy

• CPU registers
• Internal cache
• External cache
• Principal memory (RAM)
• External/secondary storing devices (Hard Discs, CDs, DVDs, pen drives, magnetic tapes, etc.)

RAM and ROM

RAM Random Access Memory (volatile, read/write)

• SRAM – Static RAM
• DRAM - Dynamic RAM
• SDRAM - Synchronous Dynamic RAM

ROM Read Only Memory (non-volatile, only read)

• PROM - Programmable ROM
• EPROM - Erasable PROM
• EEPROM - Electrically EPROM

FLASH – (non-volatile, only read/write). Pen drives, cameras….

Memory Map

Organization and structure of the addressable space in a computer. It is determined by the quantity of addresses and the size of the content of each address (word size).

• Size of address bus, m, determines number of addresses, 2^m
• Size of data bus, n, generally equals the size of the content of each address (word)