Chapter 3 and 4 - Hardware and Processor Fundamentals#

Primary Memory#

Primary storage devices are devices that hold data and instructions that are currently needed by the processor in order to manipulate the data into meaningful information.

The features of RAM:

• can be written to and read from, the data can be changed by user or computer
• store the currently in use files and programs
• volatile - temporary memory devices
• can be increased in size to improve operational speed of a computer

Differences between static and dynamic RAM

The features of ROM:

• store the data which the computer needs to access (e.g. basic input/output system BIOS) or manufacturer’s information (e.g. serial number and MAC addr.)
• non-volatile - permanent memory devices
• data can not be altered easily

Different types of ROMs

ROM - The primary memory only can be read from.

PROM - The ROM can be programmed once.

EPROM - The PROM can be further programmed by using UV light.

EEPROM - The PROM can be modified by the user, can be erased by using pulsed voltages.

Secondary Memory#

Storage Media is the physical media that holds the non-volatile data.

Storage device is a specific read/write mechanism built into to interact with a particular storage media.

Categories of Secondary storage:

• Magnetic tape
• Magnetic Disk
• Optical Disk
• Flash Memory

Magnetic discs (hard drives)

1. HDD has magnetic platters that stores the information magnetically.
2. Data is stored on sectors and tracks, each area can be independently magnetized or demagnetized.
3. read/write head moves back and forth over the platters to record or store information in binary form.
4. Part of the hard drive stores a map of sectors that have already been used up and others that are still free. When the computer wants to store new information, it takes a look at the map to find some free sectors.

Optical Discs

1. Optical storage is an electronic storage medium that uses low-power laser beams to record and retrieve digital (binary) data.
2. A laser beam encodes digital data onto an optical disk in the form of tiny pits arranged in a spiral track on the disk’s surface.
3. A low-power laser scanner is used to “read” those pits. The reflected light from the pits are converted into electric signals.

Solid State Drive SSD

SSD stores data by controlling the movement of electrons within transistors.

• NAND technology - flash memory
• NOR technology - EEPROM

Compare to HDD, the advantages of using SSD are…

• more reliable (no moving parts)
• lighter, cooler and thinner
• low power consumption
• access data considerably faster

WARNING

Principal operations of hardware devices: 更多请参见ZNotes Computer Science - Hardware的Principle Operations of Hardware Devices部分。

Von Neumann Architecture#

Von Neumann Architecture mainly focus on the CU, ALU, memory unit, I/O and many registers:

Shared Stored-program computer concept.

• instruction data and program data are stored in the same memory
• instructions are fetched and executed sequentially
• An instruction fetch and data operation cannot occur at the same time because they share a common bus.

CPU performance#

• System clock — produces timing signals to ensure synchronisation takes place. ↑ clock speed ↑ performance.

• Bus width — the number of bits can travel along the bus at a time. ↑ Bus width ↑ performance.

• Core — A unit made of ALU, CU and registers which is a part of CPU. ↑ Core number ↑ performance.

• word size — group of bits used by a computer to represent a single unit. ↑ word size ↑ performance.

Computer Port#

Port is an external connection to a computer which allows it to communicate with various peripheral devices. A number of different port technologies exist.

HDMI port — allows both audio and visual output from a computer to HDMI-enable device. This technology supports high-definition signals.

USB port — The Universal Serial Bus is an asynchronous serial data transmission method. The USB cable consists of a four-wired shielded cable (power, earth and 2 for data transmission). The USB system has become the industry standard, but there are more.

Ethernet Port — an opening on a computer to network equipment that Ethernet cables plug into. Used to connect to the device to the ethernet.

VGA - Video Graphics Array, transfer analogue signals

VGA#

Pros of VGA:

• simple.
• only one standard.
• easy to extend.
• secure connection.

Cons of VGA:

• old (out-dated).

F-E cycle#

1. Fetch — The next instruction is fetched from cache or memory.
2. Decode — The instructions are decoded into a form that ALU can understand.
3. Execute — The instructions, such as the ALU performing a computation.
4. Store — The data or results from the instruction executions are stored in memory.

Memory includes cache, registers and RAM.

Interruption#

Interruption is a signal that can cause the processor to temporarily stop what it is doing and service the interruption.

It allows the processor to do multiple task in the same time.

But it requires to store the paused program into the memory. It uses more space.

Types of Interrupts:

1. I/O Event: for example the key board event will cause interrupt so the processor is able to respond to the user’s instruction.
2. a timing signal.
3. Software error

Steps of handling an interrupt:

1. Receive the interrupt signal.
2. Processor saves the state of current program in memory.
3. Identify the interrupt type and establish the level of interrupt priority.
4. Once the interrupt has been fully serviced, the status of interrupt task is reinstated.

Register Transfer Notation (RTN)#

RTN is a short-hand notation to show movement of data and instructions in a processor. (can be used to represent of the FE cycle).

RTN Example: (Load current instruction into CIR).

1
MAR ← [PC]
2
PC ← [PC] +1
3
MDR ← [[MAR]]     // Double bracket can represent the data in memory by addressing.
4
CIR ← [MDR]

Addressing Modes#

The term addressing modes refers to the way in which the operand of an instruction is specified.

The addressing mode specifies a rule for interpreting or modifying the address field of the instruction before the operand is executed.

Types include:

• Immediate ADD #2 directly add 2
• Direct SUB [301] use the value in the address of 301 in memory
• Indirect
• Indexed x + Index register 的值
• Relative 相对于当前指令的 x 位置的值

Binary Shift.#

A shift involves moving the bits stored in a register a given number of places within the register.

• Left shift — shift the bits to the left.
• Right shift — shift the bits to the right.

Types of shift:

Logical shift — bits shifted out of the register are placed by zeros.

10110111 becomes 10111000 with 000 shifted in

Arithmetic shift — the sign of the number is preserved.

10110111 becomes 11110110 with the sign bit 1 shifted in

Cyclic shift — Bits shifted out of the right register are introduced at the opposite part of the register.